Marine Technology Society Journal

THE INTERNATIONAL, INTERDISCIPLINARY SOCIETY DEVOTED TO OCEAN AND MARINE ENGINEERING, SCIENCE, AND POLICYVOLUME 38, NUMBER 1, SPRING 2004

General Issue

E X E C U T I V E C O M M I T T E EPresidentTed BrockettSound Ocean Systems, Inc.President-ElectJerry StreeterJP Kenny, Inc.Immediate Past PresidentAndrew ClarkMaritime Communication ServicesVP-Technical AffairsDaniel SchwartzUniversity of WashingtonSecretary-TreasurerJohn HeadPrevco Subsea HousingsDirector-Budget & FinanceJerry BoatmanCOMNAVMETOCCOMDirector-PublicationsJerry WilsonFugro Pelagos, Inc.Director-Public AffairsRichard ButlerAanderaa Instruments

S E C T I O N SVP-EASTERN REGIONRobert WinokurOceanographer of the NavyCanadian MaritimeFerial El-HawaryB.H. Engineering Systems, Ltd.New EnglandJames CaseSAICWashington, DCBarry StameyMitretek SystemsVP-SOUTHERN REGIONSandor KarpathyStress Subsea, Inc.FloridaDoug BriggsFlorida Atlantic UniversityGulf CoastLaurie JuganPlanning Systems, Inc.HoustonJohn Whites, IIISubmar, Inc.VP-WESTERN REGIONBrock RosenthalOcean InnovationsHawaiiWilliam FriedlCEROSLos AngelesJames EdbergConsultantMonterey BayMark BrownMBARIPuget SoundEdward Van Den AmeeleNOAA Pacific Hydrographic BranchSan DiegoHarry MaxfieldRD InstrumentsJapanToshitsugu SakouTokai University

P R O F E S S I O N A L D I V I S I O N S& C O M M I T T E E SADVANCED MARINE TECHNOLOGYAutonomous Underwater VehiclesJustin ManleyMitretek SystemsDynamic PositioningHoward ShattoShatto EngineeringOcean EnergyOpen PositionOceanographic InstrumentationKim McCoyOcean Sensors, Inc.

Manned Underwater VehiclesWilliam KohnenSEAmagine Hydrospace, Inc.Remote SensingRichard CroutCNMOCRemotely Operated VehiclesDrew MichelTSC Holdings, Inc.

Underwater ImagingDonna KocakGreen Sky Imaging, LLCMARINE RESOURCESPorter HoaglandWHOIMarine GeodesyOpen PositionMarine Living ResourcesOpen PositionMarine Mineral ResourcesJohn C. WiltshireUniversity of Hawaii

Oceanographic ShipsOpen Position

Ocean PollutionOpen Position

Physical Oceanography and MeteorologyOpen Position

OCEAN & COASTAL ENGINEERINGCaptain Diann Karin LynnNFECBuoy TechnologyWalter PaulWHOICables and ConnectorsThomas CoughlinTomas Coughlin and Associates

DivingWilliam C. PhoelPhoel Associates Inc.Marine ArchaeologyBrett PhaneufTexas A&M UniversityMarine MaterialsOpen PositionMooringsOpen PositionOffshore StructuresOpen PositionRopes & Tension MembersJohn F. FloryTension Technology International, Inc.

Seafloor EngineeringHerb HerrmannNFESC

MARINE POLICY & EDUCATIONCoastal Zone ManagementOpen PositionMarine EducationSharon H. WalkerUniversity of Southern Mississippi

Marine Law and PolicyMyron NordquistUniversity of VirginiaMarine RecreationOpen PositionMarine SecurityOpen PositionMerchant MarineOpen PositionOcean Economic PotentialOpen PositionOcean ExplorationPaula Keener-ChavisNOAA Coastal Services Center

S T U D E N T S E C T I O N SFlorida Atlantic UniversityCounselor: Douglas BriggsFlorida Institute of TechnologyCounselor: Eric ThostesonMassachusetts Institute of TechnologyCounselor: Alexandra TechetRoger Williams UniversitySanta Clara UniversityCounselor: Christopher KittsTexas A&M University—College StationCounselor: Robert RandallTexas A&M University—GalvestonCounselor: Victoria JonesU.S. Naval AcademyCounselor: Cecily NatunewiczUniversity of HawaiiCounselor: R. Cengiz ErtekinUniversity of Rhode IslandCounselor: Chris BaxterUniversity of Southern MississippiCounselor: Stephan Howden

H O N O R A R Y M E M B E R SThe support of the following individuals isgratefully acknowledged.Robert B. Abel

†Charles H. BussmannJohn C. CalhounJohn P. Craven

†Paul M. FyeDavid S. Potter†Athelstan Spilhaus

†E. C. Stephan†Allyn C. Vine†James H. Wakelin, Jr.

†deceased

Marine Technology Society Officers

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Copyright © 2004 Marine Technology Society, Inc.

In This Issue

Volume 38, Number 1, Spring 2004

General Issue

3CrosstalkMTS Journal Readers’ Comments

5A Method for Rapid Hull FormDevelopment and ResistanceEstimation of CatamaransV. Anantha Subramanian, Patrick Joy

12Satellite Data Assimilation forImprovement of Naval UnderseaCapabilityPeter C. Chu, Michael D. Perry, Eric L.Gottshall, David S. Cwalina

24Use of Expert Systems for OptimumMaintenance of Marine Power PlantsK.D.H. Bob-Manuel

30The Science and Technology ofNonexplosive Severance TechniquesMark J. Kaiser, Allan G. Pulsipher,Robert C. Byrd

40A Design Study of Manned DeepSubmergence Research Vehicles in JapanDan Ohno, Yozo Shibata, Hisao Tezuka,Hideyuki Morihana, Ryuichiro Seki

52Temperature and Salinity Variabilityin the Mississippi Bight.Sergey Vinogradov, Nadya Vinogradova,Vladimir Kamenkovich, Dmitri Nechaev

F R O N T C O V E R :Isometric, profile, and body plan views of a generatedcatamaran demihull form (see pages 5-11), imagescourtesy of V. Anantha Subramanian and Patrick Joy;deep submergence research vehicle: operating depth2000m, surface navigational range 4500NM (see pages40-51), image courtesy of Japan Deep Sea TechnologyAssociation. Collage design by Michele A. Danoff

B A C K C O V E R :Examples of ocean forecast products from NOAA’sEast Coast Regional Ocean Forecast System (see pages61-79), image produced by the Environmental ModelingCenter at NOAA’s National Centers for EnvironmentalPrediction.

MTS Journal design and layout:Michele A. Danoff, Graphics By Design

61Development of a Real-time RegionalOcean Forecast System with Applicationto a Domain off the U.S. East CoastLaurence C. Breaker, Desiraju B.Rao,John G.W. Kelley, Ilya Rivin,Bhavani Balasubramaniyan

80The Legal Status of AutonomousUnderwater VehiclesCommentary by Stephanie Showalter

84Book Reviews

2 Marine Technology Society Journal

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CONTRIBUTORSContributors can obtain an information andstyle sheet by contacting the managing editorat the address listed above. Submissions thatare relevant to the concerns of the Societyare welcome. All papers are subjected to areview procedure directed by the editor andthe editorial board. The Journal focuses ontechnical material that may not otherwise beavailable, and thus technical papers and notesthat have not been published previouslyare given priority. General commentariesare also accepted, and are subject to reviewand approval by the editorial board.

Editorial BoardDan WalkerEditorNational Research Council

John F. BashBook Review EditorUniversity of Rhode Island

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Scott KrausNew England Aquarium

James LindholmPfleger Institute of Environmental Research

Phil NuyttenNuytco Research, LTD.

Bruce H. RobisonMonterey Bay AquariumResearch Institute

Terrence R. SchaffNational Science Foundation

Edith WidderHarbor Branch Oceanographic Institution

EditorialJerry WilsonPublications Director

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Emily L. SpeightMembershipCirculation Manager

3Spring 2004 Volume 38, Number 1

C R O S S T A L KA Review of the Effects of Seismic Surveys on Marine Mammals,by Jonathan Gordon, Douglas Gillespie, John Potter, Alexandros Frantzis,Mark P. Simmonds, René Swift and David Thompson(Winter 2003/2004, Vol 37, No 4)

I found this review a useful contribution for managing undersea noise appropriately. Lest wemake the common mistake of only focusing on direct auditory damage, the following quote fromthe Gordon et al. paper is appropriately cautionary:

“...changes in animals’ behavior [may] lead to physical damage...[thus, the assumption] that physicaldamage will be restricted to limited areas very close to powerful sound sources may have to berevised...behavioral responses can occur at extended ranges and are often highly variable.”

Unfortunately, this paper failed to mention the deleterious effects seismic noise may have onwhole ecosystems. It is not enough to state that marine mammals’ prey may be impacted. Noise canconceivably alter the links within food webs. The effects of past whaling, e.g., may explain thepresent reduction of the kelp forests in the Pacific Northwest. This perspective should make usrealize just how impossible it will be to fully describe the effects of our acoustic “footprint” on theoceans and how important precautionary management will be for many years to come.

Also useful would have been to highlight a problem plaguing marine mammal research on theeffects of undersea noise: conflict-of-interest. Because noise producers like the U.S. Navy and oilcompanies generally directly fund marine mammal science, results are perceived to be biased andlose all-important credibility. Preferable would be to have noise producers contribute funds to acommunal “pot” administered by a non-aligned body. Thus, expensive marine mammal researchwould be less wasted by being tainted through its funding sources.

LindyWeilgart,Ph.D.Dalhousie University

Author’s Response, continued on page 4

Reader’s Comments...

J O I N T H E C O N V E R S A TION…If you have a comment or question about this issue of the MTS Journal or a previousissue that you’d like to submit to Crosstalk, please limit it to 250 words or less and send itto: [email protected]. Please include your name, affiliation, and contact information(telephone, fax, and e-mail address), and identify the paper and author to whom yourcomments are addressed.

We look forward to hearing from YOU!


C R O S S T A L K

Authors’ Response

It is heartening to see that our review has already generated interest, and that this includes somecontroversy is inevitable given such a highly-charged and difficult subject.

With regard to seismic impact on whole ecosystems, there is but a poor understanding of howmarine acoustic pollution in general propagates through entire ecosystems, let alone impacts ofseismic surveys in particular. The authors recognize that a complete and integrated understandingneeds to take a holistic view and include all components and their interactions. Sadly, the under-standing of even the basic components is still at such a primitive level that integrating our knowledgeover entire ecosystems is as yet an unrealistic task that would involve a level of speculation beyondthat appropriate for a review article. Perhaps we will see some progress in this area at the meeting onseismic impacts on marine mammals organized by the Canadian Department of Fisheries to be held17-21 May 2004. This does not imply that these authors view seismic impact at the ecosystem levelas negligible, simply too poorly-understood and too difficult to quantify at present to make mean-ingful review comment.

Dr. Weilgart raises concern about a conflict of interest arising from marine mammal researchersworking on anthropogenic noise being directly funded by bodies responsible for creating “acousticpollution.” This is a subject of considerable and general importance as funding mechanisms and theadministration of projects can certainly affect the scientific questions that are asked, the way researchis done, and the research teams that are chosen to carry it out. However, this is primarily a politicalquestion which we feel could not be covered in a scientific review attempting to summarize research,observations, and our current factual understanding of the issue.

Dr. John Potter.Associate Director, Tropical Marine Science InstituteNational University of Singaporeand co-authors Alexandros Frantsis, Douglas Gillespie,Jonathan Gordon, Rene Swift, Dave Thompson

Reader’s Comments...


II N T R O D U C T I O N

n recent decades, catamarans have re-ceived considerable attention as vessels forresearch, transportation of passengers andcargo. They have large deck area, good seakeeping qualities when equipped with ridecontrol features, and manoeuvrability af-forded by slender and widely separated hulls.The design of a high-speed hull form shouldbe carried out so as to provide an adequatecapacity to carry a given payload at a requiredspeed. Given the owner’s requirements, thedesigner generally aims to provide afavourable form that gives sufficient inter-nal volume and deck area.

The interference effects between thedemihulls characterize the resistance of cata-marans, and this must be considered in ad-dition to the resistance of the demihulls inisolation. Two types of interference effectsspecific to catamarans can be identified:namely, viscous interference caused by theasymmetric flow around the demihulls andits effect on the viscous flow such as bound-ary layer formation and the development ofvortices, and wave interference originatingfrom the interactions between the wave sys-tems of the demihulls.

Insel and Molland (1991) have con-ducted investigations on the components of

resistance of catamarans. According to theexperimental results published by them, theviscous interference effect component of re-sistance for high speed catamarans prima-rily depends upon the L/B ratio and is muchless influenced by the spacing ratio (s/L). Theform factors established from the resistancetests were found to be considerably higherthan those for monohulls. With this in mind,the present approach considers a viscous in-terference factor β.

Couser et al. (1997) have observed thatit is unclear whether the viscous resistanceincrease is due primarily to modifcations ofthe boundary layer and velocity augmenta-tion between the demihulls or to additionalspray associated with constructive interfer-ence of the wave systems, particularly in thevicinity of the transom. In consideration ofthe above, a modified form factor, namely(1 + βk) as given by them has been used forobtaining the modified frictional resistancecomponent. An appropriate value of 1.42has been used for high speed, round bilgecatamarans (independent of demihull sepa-ration) considered here for assessment ofresistance. The wave resistance componentis obtained using Michell’s theory for slen-der vessels with a modification using a waveinterference factor (Tuck, 1987).

The focus of this paper is the combina-tion of a quick computer-aided scheme forthe catamaran hull form design together witha theoretical method to estimate the totalcalm water resistance of the developed hullforms. Results are given for a typical commonrange of catamaran sizes, which provide abetter understanding of the components ofcatamaran resistance including the influenceof hull spacing ratio and length-to-beamratio over a wide range of Froude numbers.The results are useful for a rapid first esti-mation of the powering of catamarans.

Methodology for Hull FormDevelopment

The ship hull form design is an ab initioproblem, i.e. the hull surface cannot be for-mulated entirely in terms of quantitativecriteria but must be resolved by a judiciouscombination of computational and heuris-tic methods. The flowchart for the hull sur-face generation scheme is given in Fig. 1.Since the objective here is rapid hull formgeneration, the basic data is obtained fromsimple freehand description of the hull formwith minimal body plan sections. The rawoffset data points are given in XYZ formatto form the 3-D mesh of polygon pointsand are transformed into consistent faired

A U T H O R SV. Anantha SubramanianPatrick JoyDepartment of Ocean Engineering,Indian Institute of Technology

P A P E R

A Method for Rapid Hull Form Developmentand Resistance Estimation of Catamarans

A B S T R A C TCatamarans are being built with higher speed capability for transportation of passen-

gers and for other applications. The wide deck area and large transverse stability areattractive features that account for the high demand for this class of vessels. A rapid hullform development, combined with assessment of resistance, is presented here. The hullform development is based on simple inputs for the polygon net, and using the bi-para-metric bi-quintic surface in a computer-aided development scheme, a faired 3-D surfaceis developed. The hull volume is computed and iteratively matched to the targeted vol-ume. Using the developed form, a formulation based on Michell’s theory for slender ves-sels, combining wave interference factor and viscous interference factor, is used to arriveat the total resistance of the combined hulls. The method is demonstrated for a series of9 catamaran forms. The forms have varied geometric ratios, but a common displacementof 180t. The method is presented as a rapid development and resistance assessment tool.


3-D surface data, obtained in any desirableclosely spaced digitized format. Hence start-ing with a tentative mesh, the programbuilds a smooth continuous surface, withthe original points being the weighting func-tions. Hydrostatic calculations are in-builtin the scheme in order to check the obtainedvolume of displacement with the targetedvolume. The basic B-spline technique is de-scribed in Rogers and Adams (1997). Thebi-quintic hull surface generation programdescribed in Subramanian and Suchithran(1999) is used to generate the hull surfaceof catamaran demihulls of varying length buthaving a constant volume of displacement.The number of stations and the number ofpoints in each station to be obtained are userdefined through screen input. The input datafile consists of four columns giving the co-ordinates of each point at each station inthe x, y, z, h format. x, y and z denote thelongitudinal, transverse, and vertical coor-dinates, respectively. The fourth column his for homogeneous coordinate representa-tion and the value is kept as unity. The in-put is to be given for one demihull, stationsstarting from the aft to forward. The pro-gram uses 2-D B-spline interpolation at ev-ery station to regenerate an equal numberof control polygon points. After generationof the control polygon points, the programfairs a B-spline surface through them. Thefairness of the curves depends upon the or-der of the curve and the number of definingpolygon points. A script file is generated asoutput containing the output points, whichis formatted for directly interfacing withAutoCAD. The drawing thus obtained canbe processed further.

A Cartesian product B-spline surface isdefined by,

Q (u, w) = ∑∑+

=

+

=

1

1

1

1

n

i

m

jB

i,j N

i,k (u) M

j,l (w)

Bi,j’s are the vertices of a defining polygon

net. The indices n and m are the number ofdefining polygon vertices in the u and wparametric directions, respectively. N

i,k(u)

and Mj,l(w) are the B-spline basis functions

in the bi-parametric u and w directions, re-spectively. k and l are the order of the curves

in the u and w directions respectively. The definition for the basis functions is given below.

Ni,1

(u) = 1 if ai ≤ u < a

i+1

= 0 otherwise

Ni,k

(u) = [(u – ai)N

i, k-1(u) / (a

i+k-1 – a

i)] + [(a

i+k – u)N

i+1, k-1(u) / (a

i+k – a

i+1)]

Mj,1

(w) = 1 if bj w < b

j+1

= 0 otherwise

Mj,l (w) = [(w – b

j)M

j, l-1(w) / (b

j+l-1 – b

j)] + [(b

j+l – w)M

j+1, l-1(w) / (b

j+l – b

j+1)]

ai and b

j are elements of knot vectors. There are three types of knot vectors that can be used,

namely, uniform, open and non-uniform knot vectors. It is not essential to use the same typeof knot vectors in both parametric directions.

The B-spline surfaces have well known properties of ability to be locally controlled inshape by means of choice of order, choice of knot vectors, modification of local shape by re-defining knots by means of knot removal and knot insertion algorithm. The references givedetails for implementation of these schemes to rapidly evolve a faired form.

FIGURE 1Flowchart for surface generation program


Estimation of Total CalmWater Resistance

The total calm water resistance of cata-marans is due to the two major components,namely, frictional resistance and wave resis-tance and, in addition, the interference ef-fects between the demihulls have to be con-sidered. These effects consist of viscous in-terference caused by the asymmetric fluidflow around the demihulls and its effect onthe viscous flow such as the formation ofthe boundary layer and the development ofvortices, and the wave interference causedby the interactions between the wave-sys-tems of the demihulls.

The well known ITTC 1957 frictionresistance line can be used to estimate theequivalent frictional resistance,

CF = 0.075/(log

10 Re – 2)2 (1)

Tuck (1987) used a mathematical for-mulation for the computation of wave resis-tance for catamarans in deep waters basedon the theory developed by Michell for slen-der vessels. The formula for the wave resis-tance of a catamaran in an unbounded seacan be expressed as,

RW

= (ρg4/πU6) (P2 + Q2) sec5θ dθ

P and Q are the Michell wave functionsdefined by,

P + iQ = f b(x,z) e(iwox + koz) dz dx

b(x,z) is the local beam of the demihull. θ isthe wave angle. U is the speed of the vessel.The wave interference factor f for a catama-ran is given as,

f = 2 cos(uo.s/2)

s is the spacing between the center-planes ofthe demihulls. k

o, u

o and w

o are the circular,

transverse, and longitudinal wave numbers,respectively, and are given as,

ko = (g/U2) sec2θ

uo = k

o sin θ

wo = k

o cos θ

The coefficient of wave resistance forcatamarans may be expressed as,

CW

= RW

/(ρAW

U2) (2)

where, r is the density of sea water which istaken as 1025 kg/m3 at 150 C. A

W is the

wetted surface area of the demihull.The total calm water resistance of cata-

marans, in the coefficient form may be ex-pressed as,

CT = (1 + βk) C

F + C

W (3)

The viscous interference factor (β) de-pends upon the speed of the vessel, slender-ness ratio, and the hull spacing ratio. For amonohull, β =1. For practical purposes, theviscous interference factor is combined withthe form factor (1 + k). An average value of1.42 is assumed for the modified form fac-tor (1 + βk) from experimental results(Couser et al., 1997).

Description of GeneratedParametric Hull Forms

In principle, the method described canbe used to evaluate resistance for the hull ofany targeted displacement and speed. As anillustration, the method is demonstrated for

a series of catamaran forms with a targeteddisplacement of 180 tonnes and Froudenumber up to 1.0. This range has been cho-sen as a value typical of common high-speedcatamarans being built today, mainly forpassenger transportation. The hull form con-forms to the general body plan shapes of theNordstrom series, but has been generatedwith simple raw inputs as described earlier.Nine catamaran demihull forms correspond-ing to three different lengths are generated.The lengths considered here are 30 m, 40 mand 50 m. The volume of displacement forall the forms is kept constant at 90 m3 foreach demihull. For each length, three dif-ferent breadths are chosen and the draughtis varied so as to maintain the volume of dis-placement. The isometric view and profileview of a generated hull form are shown inFig. 2. The body plan views of the generatedcatamaran demihull forms are shown in Fig.3 to 5. The hull form parameters for the gen-erated forms are given in Tables 1 to 3. Thecoefficient of total resistance is computed forthe generated forms by considering four dif-ferent hull spacing ratios as given in Fig. 6 to9. In order to bring out the comparative val-ues of wave resistance coefficient C

w for the

same length of hull, with different spacingratios, Fig.10 shows a sample plot for thecase of L=30m and different s/L ratios.

FIGURE 2Isometric and Profile view of a generated catamaran demihull form (L = 30 m)

π/2

0

L/2 0

–L/2–T


FIGURE 3Body plan views of the generated demihull forms(L = 30 m)


Parameter Form 1 Form 2 Form 3

b (m) 3.20 3.60 3.90

D (m) 3.00 3.00 3.00

T (m) 1.78 1.86 1.70

bWL (m) 3.00 3.28 3.56

CB 0.57 0.49 0.49

CP 0.60 0.52 0.67

AW (m2) 130.40 131.10 125.20

L / b 9.37 8.33 7.69

b / T 1.79 1.93 2.29

L / ∇ 1/3 6.69 6.69 6.69

TABLE 1Hull form parameters (L = 30 m, ∇ = 90 m3)


b (m) 3.20 3.40 3.60

D (m) 3.00 3.20 3.20

T (m) 1.70 1.65 1.60

bWL (m) 2.70 2.92 3.12

CB 0.48 0.47 0.46

CP 0.67 0.65 0.62

AW (m2) 155.50 152.40 151.10

L / b 12.50 11.76 11.11

b / T 1.88 2.06 2.25

L / ∇ 1/3 8.92 8.92 8.92

TABLE 2Hull form parameters (L = 40 m, ∇ = 90 m3)



FIGURE 6Coefficient of total resistance (s/L = 0.15)


b (m) 3.20 3.60 4.00

D (m) 3.00 3.00 3.00

T (m) 1.50 1.40 1.25

bWL (m) 2.77 3.06 3.34

CB 0.45 0.43 0.43

CP 0.94 0.92 0.90

AW (m2) 173.00 169.20 166.53

L / b 15.62 13.89 12.50

b / T 2.13 2.57 3.20

L / ∇ 1/3 11.15 11.15 11.15

TABLE 3 Hull form parameters (L = 50 m, ∇ = 90 m3)





ConclusionsA computer-aided surface development

scheme based on the B-spline surfaces is usedto generate high speed catamaran hull forms.The scheme has been applied to generatetypical high-speed catamaran hull forms ofdisplacement 180 tonnes. The user definedinput data (control polygon net) can be re-fined iteratively to generate hull forms oftargeted displacement and other hydrostaticparticulars. Based on a given range of geo-metric parameters, nine catamaran demihullforms are generated. The forms are groupedinto three sets of three forms each. Thelength (LBP) is varied over the sets as 30 m,40 m and 50 m respectively. The breadth tothe draught ratio (b/T) is varied for eachform to maintain the volume of displace-ment. All forms are symmetric about theircenter-planes and have round bilge form.The fairness of the surface is evaluated in thesense of being pleasing to the eye of the de-signer. This is enough for the present pur-pose of estimating resistance. However amore objective standard of fairness such asbased on curvature criteria can be set for rig-orous development of hull forms.

The total calm water resistance of cata-marans is mainly affected by the wetted sur-face area, the slenderness ratio (L/∇ 1/3) and

the hull spacing ratio (s/L). The followinginferences can be made from the calculatedvalues of the total calm water resistance forthe generated hull forms:1. The total calm water resistance increases

with length and speed of the vessel.2. For a particular length and speed, the

total resistance decreases with increasinghull spacing ratio (s/L).

3. For a particular length, speed, and hullspacing ratio, the total resistanceincreases with increasing (b/L) ratio and(b/T) ratio.

4. Thus when geometric ratios are con-straints, the method permits rapid formdevelopment and assessment of resistancecharacteristics.

The wave interference influences thetotal resistance to a large extent, particularlyat lower speeds (Fn < 0.35). The beneficialwave interference (hollows) is achieved bythe cancellation of a part of the divergentwave systems of each demihull, whereas ad-verse wave interference (humps) arises oninteraction of the transverse wave systems.Above a particular speed (Fn > 0.5), the waveinterference factor which is dependent onhull spacing ratio and speed takes a constant


value due to which the wave interference haslittle effect on the total resistance at higherspeeds. The present method is useful in thepreliminary design of catamarans and forrapidly obtaining form ratios and thereforefavourable resistance characteristics.

ReferencesCouser, P.R., A. F. Molland, N.A. Armstrong

and I.K.A.P. Utama. 1997. Calm water

powering predictions for high speed catamarans.

Proceedings International Conference of Fast Sea

Transportation (FAST’ 97), Sydney, July 1997.

Insel, M. and A.F. Molland. 1991 An investigation

into the resistance components of high speed

displacement catamarans. Trans. RINA

Rogers, D.F. and J.A. Adams. 1997. Mathematical

elements for computer graphics. New Delhi:

Tata McGraw Hill Publishing Company Ltd.

Subramainan, V.A. and P.R. Suchitran. 1999.

Interactive curve fairing and bi-quintic surface

generation for ship design. Intl. Shipbuilding

Progress, 46(44).

Tuck, E.O. 1987. Wave resistance of slender

ships and catamarans, Report T8701

University of Adelaide.


EI N T R O D U C T I O N

ven with all the high technologyweapons onboard U.S. Navy ships today,the difference between success and failureoften comes down to our understandingand knowledge of the environment inwhich we are operating. Accurately pre-dicting the ocean environment is a criti-cal factor in using our detection systemsto find a target and in setting our weap-ons to prosecute a target (Gottshall, 1997;Chu et al., 1998). From the ocean tem-perature and salinity, the sound velocityprofiles (SVP) can be calculated. SVPs area key input used by U.S. Navy weaponsprograms to predict weapon performancein the medium. The trick lies in findingthe degree to which the effectiveness ofthe weapon systems is tied to the accu-racy of the ocean predictions.

The U.S. Navy’s Meteorological andOceanographic (METOC) communitycurrently uses three different methods toobtain representative SVPs of the ocean:climatology, in situ measurements, anddata (including satellite data) assimilation.

The climatological data provides the back-ground SVP information that might notbe current. The Generalized Digital En-vironmental Model (GDEM) is an ex-ample of a climatological system that pro-vides long-term mean temperature, salin-ity, and sound speed profiles. The in situmeasurements from conductivity-tem-perature-depth (CTD) and expendablebathythermograph (XBT) casts may giveaccurate and timely information, but theseare not likely to have large spatial and tem-poral coverage over all regions where U.S.ships are going to be operating. In a dataassimilation system, an initial climatologyor forecast is improved by using satelliteand in situ data to better estimate synop-tic SVPs. The Modular Ocean Data As-similation System (MODAS) utilizes seasurface height (SSH) and sea surface tem-perature (SST) in this way to makenowcasts of the ocean environment (Foxet al., 2002).

The value added by satellite data as-similation for use of undersea weapon sys-tems can be evaluated using the SVP in-

A U T H O R SPeter C. ChuMichael D. PerryNaval Ocean Analysis and PredictionLaboratory, Department of Oceanography,Naval Postgraduate SchoolMonterey, CA

Eric L. GottshallSpace and Naval Warfare System CommandSan Diego, CA

David S. CwalinaNaval Undersea Warfare CenterNewport, RI

P A P E R

Satellite Data Assimilation for Improvementof Naval Undersea Capability

A B S T R A C TImpact of satellite data assimilation on naval undersea capability is investigated

using ocean hydrographic products without and with satellite data assimilation. Theformer is the Navy’s Global Digital Environmental Model (GDEM), providing a monthlymean; the latter is the Modular Ocean Data Assimilation System (MODAS) providingsynoptic analyses based upon satellite data. The two environmental datasets are takenas the input into the Weapon Acoustic Preset Program to determine the suggestedpresets for an Mk 48 torpedo. The acoustic coverage area generated by the programwill be used as the metric to compare the two sets of outputs. The output presetswere created for two different scenarios, an anti-surface warfare (ASUW) and ananti-submarine warfare (ASW); and three different depth bands, shallow, mid, anddeep. After analyzing the output, it became clear that there was a great difference inthe presets for the shallow depth band, and that as depth increased, the differencebetween the presets decreased. Therefore, the MODAS product, and in turn the sat-ellite data assimilation, had greatest impact in the shallow depth band. The ASWpresets also seemed to be slightly less sensitive to differences than did presets inthe ASUW scenario.

put data from MODAS (with satellite dataassimilation) and GDEM (climatologywithout satellite data assimilation). Thequestion also arises of how many altim-eters are necessary to generate an optimalMODAS field. Too few inputs could re-sult in an inaccurate MODAS field, whichin turn could lead to decreased weaponeffectiveness. There must also be somepoint at which the addition of anotheraltimeter is going to add a negligible in-crease in effectiveness. This superfluousaltimeter would be simply a waste ofmoney that could be spent on a more use-ful system.

The purpose of this study is to quan-tify the advantage gained from the use ofdata from MODAS assimilation of satel-lite observations rather than climatology.The study will specifically cover the ben-efits of MODAS data over climatologywhen using their respective SVPs to deter-mine torpedo settings. These settings re-sult in acoustic coverage percentages thatwill be used as the metric to compare thetwo types of data.


2. Navy’s METOC Modelsand Data

2.1. GDEMGDEM is a four dimensional (latitude,

longitude, depth and time) digital modelmaintained by the Naval OceanographicOffice. GDEM was generated using overseven million temperature and salinity ob-servations, most of them drawn from theMaster Oceanographic Observation DataSet (MOODS). Globally GDEM has a reso-lution of 1/2º degree. However, in a few se-lect areas, higher resolutions are available.In order to represent the mean vertical dis-tribution of temperature and salinity for gridsquares, GDEM determines analyticalcurves to fit to the individual profiles (Teagueet. al., 1990; Chu et al., 1997, 1999)

Before curves can be fitted to the data,quality control must be implemented thatremoves anomalous features or bad obser-vations. The data is checked for proper rangeand static stability, and it is checked to en-sure that it has not been misplaced in loca-tion or season. Once the data has been in-spected for quality, curves are fitted to thedata. From the mathematical expressionsthat represent the curves, coefficients aredetermined. It is these coefficients that willbe averaged. It can be shown that the coeffi-cients resulting from averaged data are notthe same as the averaged coefficients of thedata. In order to minimize the number ofcoefficients necessary to generate smoothcurves, different families of curves are usedfor different depth ranges. This necessitatesthe careful selection of matching conditionsin order to ensure that no discontinuities inthe vertical gradients occur. Separate com-putation of temperature and salinity allowthe results to be checked against each otherto ensure stable densities.

2.2. MODASMODAS is a collection of over 100

FORTRAN programs and UNIX scriptsthat can be combined to generate a numberof different products (Fox et al., 2002). Afew examples of MODAS programs includedata sorting, data cross-validation, data as-similation, and profile extension. This

modularity allows MODAS to be quicklyand easily modified to handle problems ornew requirements as they arise. MODAShas varying degrees of resolution starting at1/2º in the open ocean increasing to 1/4º incoastal seas and increasing again to 1/8º nearthe coast (Fox et al., 2002). To generatenowcasts and forecasts, the MODAS sys-tem uses a relocatable version of thePrinceton Ocean Model (POM). To initial-ize the POM MODAS temperature andsalinity grids, geostrophically estimated cur-rents, or extracted currents from otherPOM’s can be used.

One of the most important features ofMODAS is its use of dynamic climatology(Fox et al., 2002). Dynamic climatology isthe incorporation of additional informationinto the historical climatology in order toportray transient features that are not repre-sented by the climatology. Two useful quan-tities that are easily gathered from satellitesare sea surface height (SSH) and sea surfacetemperature (SST). While SST from altim-eters can be used directly, the SSH, which ismeasured as the total height relative to theproscribed mean, must be converted into asteric height anomaly in order to be used.2D SST and SSH fields are generated frompoint observations through the use of opti-mal interpolation.Optimal interpolation is a process by whichthe interpolated temperature or salinityanomaly is determined as the linear combi-nation of the observed anomalies. Each ofthe anomalies is given a weight that accountsfor variation in temporal and spatial sam-pling. Weights are computed by minimiz-ing the least square difference between theinterpolated value and the true value at thegrid point and by solving the equations(Gandin, 1965),

where αi are the weights, λ is the signal to

noise ratio, µij is the autocorrelation betweenlocations i and j, and µGi is theautocorrelation between the grid point and i.For each grid node location matrix inversionis used to solve the system of N equations

for the N unknown weights. The other pa-rameters are computed using the first guessfield, MOODS profiles, and climatology.Using this process any new observation canbe interpolated into the appropriateMODAS grid node.

The first guess field, the prior day’s 2DSST field, or the weighted average of 35 daysof altimeter data respectively, is subtractedfrom the new observations, and the result-ing deviations are interpolated to produce afield of deviation. This is added to the firstguess field to generate the new 2D field. Forthe first iteration of the optimal interpola-tion, climatology is used for SST and theSSH measurement is assumed to have a zerodeviation. This means that until the fielddeviates from the climatology, the extra datahas added no value and MODAS reverts toclimatology.

Once the data is in a useful form,MODAS begins with the climatology pro-file and then correlates variations in the SSHand SST to variations in the subsurface tem-perature. The regression relationships usedhere were constructed by performing a least-squares regression analysis on archived tem-perature and salinity profiles. This is a threestep process starting with the computationof regional empirical orthogonal functionsfrom the historical temperature and salinityprofiles. The second step is to express theprofiles in terms of an empirical orthogonalfunction series expansion. The final step isto perform regression analysis on the profileamplitudes for each mode, truncating theseries after three terms. This is possible be-cause of the compactness of the empiricalorthogonal function representation.

Once the subsurface temperatures havebeen revised, MODAS adjusts the subsur-face salinity profile using the relationshipbetween temperature and salinity. Thisnew profile is referred to as a syntheticprofile. Synthetic profiles only utilize theseregression relationships down to a depthof 1500 m due to the decreasing reliabil-ity of the relationships at depth (Fox etal., 2002).

MODAS is also able to include mea-surements from in situ CTDs and XBTs. Thefirst guess field is the field generated by the

Σ α j µ

ij + λ–2α

i = µ

Gi , (1)N

j=1


dynamic climatology, and the in situ pro-files are subtracted from it to get residuals.Optimal interpolation is once again used toupdate the temperature field and from thetemperature field the salinity field can begenerated. This salinity field then serves as afirst guess field for the inclusion of the salin-ity profiles (Fox et al., 2002).

2.3 Satellite Altimetry DataAssimilated into MODAS

The Navy currently uses satellite al-timeters and inferred data to assess theocean environment for the naval opera-tions. Of primary interest is mesoscalevariability. Meandering fronts and eddiescan significantly change the temperatureand salinity structure of the ocean. Thisimportance is clearly seen in sonar depen-dent operations such as anti-submarinewarfare (ASW). Sonar range can be greatlyhelped or hindered by the acoustic envi-ronment created by the salinity, tempera-ture, and density. Altimeters also providethe SSH measurements that MODAS usesin its optimal interpolation.

While monitoring mesoscale variabilityis of prime importance to the Navy, anemerging secondary role for Navy altimetersis monitoring continental shelf and coastalzones. As the Navy conducts more and moreoperations in littoral waters, the ability topredict near-shore parameters will have in-creasing importance. Altimeter data can beused to get up-to-date information on rap-idly changing near-shore characteristics suchas tides and wave height (Jacobs et al., 2002).These are important issues for anyone deal-ing with mine detection, beach operations,or ship routing.

Altimeters have also been used to mea-sure the flow through important straits, suchas the Tsushima Strait, and to measure large-scale circulation. The first of these helps re-searchers and modelers to develop con-straints on local numerical models. Large-scale circulation measurements can also helpin the development of models by aiding inerror correction. They also help explain thelocal environment that is often affected bynot just local forcing, but large-scale circu-lation variations as well.

Satellite altimeters can provide a greatvariety of data, but no single altimeter canprovide measurements on all desired timeand length scales. Different parameters mustbe sampled at different frequencies if theyare going to be of any use. For instance, seasurface height must be sampled every 48hours while wave height must be sampledevery three hours. While different ocean fea-tures all have different time and spatial scales,only the requirements for observation ofmesoscale features are presented here as anexample (Jacobs et. al., 1999).

In order for an altimeter to efficientlyand accurately sample mesoscale features,there are several requirements placed on itsaccuracy, orbit, and repeat period. A satel-lite altimeter must produce measurementsthat are accurate to within 5 cm, or the er-rors that propagate down into the tempera-ture and salinity calculations will be unac-ceptable. With an error of only 5 cm, theerror in the temperature calculation can be1-2° C. Satellites should also have an ex-act repeat orbit to maximize the usefulnessof the data collected. Without an exact re-peat orbit, the only way to get differencesin sea surface heights is to use only the datafrom points where the satellite crosses thetrack of another altimeter or itself. An ex-act orbit is considered to be a 1 km wideswath of a predefined ground track. Fi-nally, the period of a single satellite shouldbe greater than the typical 20 day time scaleof a mesoscale feature. If two satellites areused, then they should be spaced so that apoint on the ground is not sampled morethan once in a 20 day period (Jacobs et.al., 1999).

As described earlier, systems such asMODAS rely heavily on the informationprovided by these satellites. MODAS usesinterpolation to estimate SSH at pointsthat the satellite did not cover. If theground track spacing is too coarse thenthe optimal interpolation scheme ofMODAS will begin introducing errorsinto the fields between the tracks. It isimportant that the satellites be properlyset up so that a maximum amount of in-formation can be gathered with a mini-mum amount of error.

3.Navy’s Weapon Acoustic PresetA Weapon Acoustic Preset Program

(WAPP) is used to get automated, interac-tive means of generating Mk 48 and Mk 48Advanced CAPability (ADCAP) acousticpresets and visualizing torpedo performance.It combines the Mk 48 Acoustic Preset Pro-gram (M48APP) and the Mk 48 ADCAPAcoustic Preset Program (MAAPP) into asingle integrated package. The Royal Aus-tralian Navy as a part of the Collins ClassAugmentation System (CCAS) also uses theM48APP, and the Royal Canadian Navy haschanged the M48APP for Java. The programis based around a graphical user interfacethat allows the user to enter the environmen-tal, tactical, target, and weapon data. Withthese user specified parameters, the programthen performs a series of computations togenerate accurate acoustic performance pre-dictions. The output includes a ranked list-set of search depth, pitch angle, LD, andeffectiveness values, an acoustic ray trace, anda signal excess map (Cwalina, 2002, per-sonal communication).

The Environmental Data Entry Mod-ule (EDE) is a simple Graphic User Inter-face (GUI) that allows the user to enter avariety of environmental parameters (Fig. 1).The sea surface fields allow the user to specifywind speed, wave height, and sea state basedon either the World Meteorological or Beau-fort scale conventions. The three fields arecoupled so that an entry into one field willbring up the appropriate default values forthe others. The bottom condition field al-lows the user to specify the bottom depthand to choose the bottom type from a list ofpossibilities. The bottom of the GUI is de-voted to the water column characteristics anda sound speed profile. The temperature,sound speed, and depth are all in the appro-priate English units. The volume scatteringstrength (VSS) is in dB. The additional fieldsinclude the latitude, longitude, the profilename, and the table group identifiers.

Once the environmental parametershave been entered, the user can move on tothe Acoustic Module Preset Display. ThisGUI allows the user to specify a number ofparameters about the weapon, the target, andthe way the weapon should search (Fig. 2).


The list-set on the right side of the GUI dis-plays a series of search depths, pitch angles,laminar distances, and effectiveness values.The effectiveness values for the various pre-sets are based on expected signal excess andray trace computations. Both plots can beviewed from a pull-down menu. These pro-vide a visual representation of the acousticperformance of the Mk 48.

In addition to automatically computingthe most effective preset combination for agiven set of environmental parameters, theprogram also allows the user to manuallyexamine the effectiveness of any allowablepreset combination via the signal excess andray trace plots. The program also allows theuser to save the tactical preset list and theaccompanying environmental data. The dataare stored locally in the weapon module andcan be recalled later or transferred via a net-work to the combat control system.

4. Statistical Analysis

4.1. Input and Output DifferenceThe difference between the two sets of

input (GDEM and MODAS) ψ input , orbetween the two sets of output weapon pre-set data (running using GDEM andMODAS) ψ output ,

∆ψ (r,t) = ψ Μ (r ,t) – ψ G (r,t) , (2)

represents the ocean data update using sat-ellite and in situ observations (input) andthe effect of using satellite and in situ obser-vations on the weapon preset (output). Hereψ

M and ψ

G are the variables (either input

or output) using GDEM and MODAS,respectively. We may take the probabilityhistograms of ψ

M and ψ

G to show the

difference between the statistical characteristics.

4.2. Root Mean Square DifferenceGDEM and MODAS have different

grid spacing: 1/2º x 1/2º in GDEM and1/12º x 1/12º in MODAS. For a GDEMcell, one data is available for GDEM and 36data for MODAS. The root-mean-squaredifference (RMSD),

FIGURE 1Environmental data entry.

FIGURE 2Acoustic preset module display.


is commonly used to represent the differ-ence in the input and output data. Here, N(=36) is the total MODAS data number ina GDEM cell. The RMSD can be computedfor either the input data to the weapon pre-set model such as the temperature, salinity,or sound speed, or it can be computed forthe output data such as nondimensional de-tection area.

5. Comparison betweenGDEM and MODAS in theGulf Stream Region

5.1. DataIn order to make a meaningful compari-

son of MODAS and GDEM data, a suffi-ciently large data set had to be obtained. TheArea of Interest (AOI) also needed to be anarea where the ocean environment fluctuatedon a fairly short time scale. The GDEM datain March and MODAS data on March 15,2001 was obtained for the area off the NorthAmerican coast corresponding to 40°-35° Nlatitude and 75°-70° W longitude (Fig. 3).

Due to the differing resolutions ofGDEM and MODAS, this area provided117 GDEM profiles and 1633 MODASprofiles (Fig. 4). Each profile was simply atext file that consisted of a header row andcolumns of data. The header row containedthe number of depths the profile covered,the file’s name and the latitude and longi-tude of the profile.

The columns corresponded to depth infeet, the temperature in degrees Fahrenheit,the sound speed velocity in feet per second,a volume backscatter value, and salinity inPSU. Despite the common use of Interna-tional units in scientific experiments, it wasnecessary for the profiles to be set up in theappropriate English units. The WeaponAcoustic Preset Program (WAPP), the pro-gram used to generate the presets from theprofiles, requires inputs to be in English units.

RMSD = , (3)

FIGURE 3Area of interest.

5.2. Difference between GDEMand MODAS

While GDEM gives the climatologicalbackground ocean environment at a givenplace, MODAS is expected to provide morecurrent and synoptic interpretations of theenvironment. The amount of accuracyMODAS adds is in proportion to the scaleon which ocean parameters vary. For areassuch as the Gulf Stream, where environmen-tal factors are known to vary rapidly on arelatively small time scale, it is expected thatthere would be at least a few areas where thetwo data sets differ. It is these areas that areof particular interest, since the difference inthe weapon presets should be greatest.

On the surface, the GDEM data pro-vided a view of the temperature distributionthat consisted of smooth, uniformly spacedlines of constant temperature that were con-sistent with the overall flow of the region(Fig. 5). The cool water on the shelf gradu-ally gives way to the warm water flowing

FIGURE 4 GDEM and MODAS data points


north along the Gulf Stream. The GDEMgenerated surface salinity distribution is ex-tremely similar to the surface temperaturedistribution and is consistent with the GulfStream region. Fresher water lies inland andthe salinity increases with distance from theshore. The only variation is in the north-eastern section, where there is a slight intru-sion of the salty offshore water.

As expected, the GDEM and MODASdistributions are, overall, fairly similar in boththeir range of values and overall distribution.They are similar to each other in shape, andboth show areas of cool fresh water near thecoast and areas of warm salty water lying off-shore. There are, however, a few differences,with the intrusion of warm salty water inthe northeastern section of the MODAS fig-ure being the most notable. There is also anarea of high temperature in the lower rightcorner of the MODAS figure that does notshow up in the GDEM figure. In general,the MODAS figure shows a sharper frontwith the water increasing in temperature andsalinity much more rapidly as the distancefrom the coast increases (Fig. 6). The GDEMfigure shows a gradual increase in tempera-ture and salinity starting in the top left cor-ner and continuing almost entirely down tothe lower right corner. The MODAS figureshows the water reaching maximum tem-

perature and salinity quickly and then stay-ing constant to the lower right corner.

While the GDEM and MODAS dataoffer similar ranges of temperatures, salini-ties, and sound speeds at the surface, thedistribution of the values is quite different.The histograms in Figure 7 reveal that whilethe temperature values reported by both datasets are similar, the MODAS data has a

higher proportion of profiles located in the6°-7° C range. The difference in the salinitygraphs is even more drastic with the bulk ofthe GDEM values located in the middle ofthe range and the MODAS values split be-tween the high and low ends of the range.The sound speed graph indicates thatMODAS typically reports higher soundspeeds than does the GDEM data. This isnot too surprising, since sound speed in theupper water column tends to be tied closelyto temperature, and the MODAS data in-dicates warmer water than the GDEM data.

Increasing depth to 50 m and then 100m, it is clear to see that, for temperature, thedistribution of the values over the range forboth sets of data is quite similar. There isstill a slight preference in the MODASgraphs towards higher temperatures, but itis not as drastic as is seen on the surface.Salinity is much the same, with the differ-ence in shapes of the two figures more a fac-tor of the small number of GDEM profilesas compared with the number of MODASprofiles. Sound speed is the only area wherethe two data sets continue to diverge. Fromthe 50 m and 100 m sound speed figures itis clear that, with depth, the MODAS dataindicates increasing sound speed and theGDEM data predicts some sort of sound

FIGURE 5March surface temperature and salinity distribution from GDEM.

FIGURE 6MODAS generated surface temperature and salinity distribution on March 15, 2001.


speed minimum at depth. This is causingthe peak on the MODAS graph and the peakon the GDEM graph to move away fromeach other as depth increases.

By 2000 m the temperature and salinityhistograms for the two data sets are virtuallyidentical. At this point any perceived differ-ence in the two is solely a factor of the dif-ference in the number of profiles betweenthe two data sets. For the sound speed fig-ures this is the point of maximum separa-tion. The GDEM data indicates low soundspeeds representative of a deep sound chan-nel, whereas the MODAS data indicates thatthe sound speed has increased to this point.After this point the GDEM values begin ris-ing again to match the MODAS data.

While the distribution of the values overthe range is a useful tool in examining theinputs, it is the difference between the in-puts that is of real importance. Figure 8shows the RMS difference of the inputs.From the surface temperature figure in Fig-ure 8, the RMS difference of temperaturepeaks out in the lower left corner of the AOIat about 2° C. Besides the peak, the othersignificant area is the ridge starting in thelower left corner and running to the middletop of the figure. This corresponds to a nar-row region where the GDEM distributionwarmed slower than the MODAS distribu-tion moving from the coast out to sea. Thewarm water intrusion is represented by thegradual increase in height of the ridge. Thesalinity difference at the surface is nearly zerofor most of the AOI and reaches its maxi-mum value of 4.5 PSU along the top of theregion. The derived sound speed RMS dif-ference, as expected, is smallest far from thecoast where the difference in temperatureand salinity is smallest and increases towardsthe coast.

As depth increases, the RMS differencein temperature and sound speed changesslowly, but the difference in salinity drops offquickly. Neither the temperature nor soundspeed difference change significantly, but by100 meters the RMS difference for salinityhas gone down to values of less than .8 PSU.From 100 meters down, the temperature dif-ference begins to decrease slowly, and by 2000meters the RMS difference for both tempera-

FIGURE 7Comparison between GDEM and MODAS temperature histogramsat (a) the surface, (b) 100 m depth, and (c) 2000 m depth.


ture and salinity has dropped to negligiblelevels for most of the AOI. This is expectedsince MODAS reverts to climatology atdepth. Except for the profiles in the north-western corner of the AOI that did not runas deep as the other profiles farther from thecoast, all the RMS difference vs depth pro-files were remarkably similar. All of the tem-perature differences showed either a gradualdecrease in the difference down to about 1000meters or a slight increase in the differenceimmediately followed by a gradual decreasein the difference down to 1000 meters. Atabout 1000 meters the temperature differ-ences all rapidly dropped to near zero.

The sound speed profiles all show thedifference increasing down to a maximumvalue of 60 m/s at around 2000 meters. Af-ter that the RMS difference drops off, andapproaches zero by 3000 meters. The causeof the maximum at 2000 meters is lack of adeep sound channel according to theMODAS data. The MODAS profiles al-most all have the sound speed steadily in-creasing down to the maximum depthwhereas climatology indicates a sound speedminimum at 2000 m. While there is somevariation in how quickly the salinity differ-ences drop to near zero, they are less than 1PSU by 200 meters. Shown in Figure 9 is arepresentative RMS difference profile.

6. Comparison of WeaponAcoustic Preset UsingGDEM and MODAS

The raw data was processed by the Na-val Underwater Warfare Center (NUWC)Division Newport. They received the inputprofiles, ran them through the WAPP, andgenerated the output. Percentage coveragewas calculated based on both surface(ASUW) and submarine (ASW) scenarios.The submarine scenario is a low Dopplerscenario consistent with diesel submarineoperations. The coverage percentages repre-sent coverage in the target depth band, ei-ther shallow, mid, or deep. The coveragepercentages were also normalized over acous-tic modes to produce an output that wasdimensionless.

FIGURE 8Horizontal dependence of RMSD at the surface between GDEM and MODAS for(a) temperature, (b) sound speed, and (c) salinity.


6.1. Output DistributionsThe output provided by NUWC from

the WAPP runs consisted of twelve differ-ent percentage coverage groups, three depthbands times two scenarios times the two dif-ferent types of input data. For the non-SVPderived WAPP inputs, consistent values wereused throughout the runs to ensure that anydifference in the outputs was a result of dif-ferences in the GDEM and MODAS data.For each of the groups, basic statistics suchas mean, maximum, minimum, and stan-dard deviation were computed and then thedata were constructed into histograms to givea visual representation of how the data aredistributed.

In the shallow depth band ASUW sce-nario both MODAS and GDEM yieldmean coverage percentages that are very closeto each other. While statistically the meansare different, in real world applications a fewpercentage points difference is negligible (Fig.10). From a user’s standpoint, this meansthat both sets of data predict about the same

mean coverage for the AOI. The ASW sce-nario yields similar results except for the factthat the two means were not even statisti-cally different. While this seems to indicatethat the two data sets are returning similarresults, there are some important differences.First are the outliers on the GDEM graphs.Values in the high thirties to low fifties areextremely rare, yet the GDEM data indicatethat in at least one location for the ASUWscenario and several for the ASW scenario,the weapon will perform to this level. TheASW scenario also has a rather significantnumber of GDEM profiles that generatebelow average coverage percentages. Thiswould indicate that GDEM predicts thatcoverage will vary greatly with location. Incomparison the MODAS values for bothscenarios tend to be very consistent. Cover-age percentage varies little with location dueto the fact that most of the profiles lie withina very narrow range. Overall GDEM pre-dicts excellent coverage some of the time andpoor coverage the rest of the time. MODASdata on the other hand, indicates that cover-age percentage will not be excellent anywherebut the expected values will be uniform overthe whole shallow depth band region.

FIGURE 9Depth dependence of RMSD between GDEM and MODAS for (a) temperature, (b) sound speed, and (c) salinity.

FIGURE 10Shallow depth band coverage percentage distributions: upper panels for GDEM and lower panels for MODAS,left panels for ASUW scenario and right panels for ASW scenario.


The mid depth band yielded results thatwere similar in distribution to the shallowdepth band (Fig. 11). Across both scenariosthe mean coverage of the GDEM data andthe mean coverage of the MODAS data arestatistically identical. Outliers are once againobserved in the GDEM data, the larger out-lier in the ASUW scenario, and the greaternumber of outliers in the ASW scenario. Thewide dispersion of the GDEM derived cov-erage indicates that weapon effectiveness willvary depending on location. This is similarto the predictions for the shallow depth bandand would indicate that GDEM predicts awater column that has varying coverage val-ues depending on horizontal and verticallocation. MODAS data once again indicatesan overall performance in the region that isslightly less than the GDEM prediction;however, the MODAS data is grouped evenmore tightly than in the shallow depth band.The coverage in the ASW scenario in par-ticular varies little about the mean value. Thisand the shallow depth band predictions in-dicate uniform coverage can be expectedeven at some depth.

In the deep depth band the graphs takeon a slightly different shape, but they con-

scenario has the larger predicted values, butthe values in the ASW scenario are still onthe upper end of what is normal. TheMODAS data predicts performance that is,while not particularly bad, still much morepessimistic than the GDEM predictions.

For both scenarios the means of theGDEM and MODAS derived predictionsare statistically different with the MODASdata providing the smaller mean in both sce-narios. Although the dispersion of theGDEM data is large in both scenarios, thedata is so heavily weighted towards the up-per end that low GDEM coverage percent-ages are average values for the MODAS datacoverage percentages. The MODAS datacoverage percentages are once again tightlygrouped; the uniformity of the predicted cov-erage percentages observed in the two otherdepth bands extends from the surface downto the selected maximum operating depth.

6.2. Difference of MK48 AcousticPresets Using GDEM and MODAS

For the shallow depth band, the RMSDin the percentage coverage area was smallover most of the AOI, consistent with thesimilar means and range of values noted inthe previous section (Fig. 13). The areas

FIGURE 11Medium depth band coverage percentage distributions: upper panels for GDEM and lower panels for MODAS,left panels for ASUW scenario and right panels for ASW scenario.

FIGURE 12Deep depth band coverage percentage distributions: upper panels for GDEM and lower panels for MODAS, leftpanels for ASUW scenario and right panels for ASW scenario.

vey much the same meaning (Fig. 12). Inboth scenarios the GDEM graphs areweighted heavily to the right end, predictingthat in the deep depth band coverage will bevery good over most of the area. The ASUW


computed to have small RMSD coveragepercentages also had small RMSD in tem-perature and salinity. In the region wherethe RMSD in temperature and salinity waslargest, though, a large RMSD in percent-age coverage is also observed. These largervalues are likely areas where the GDEMdata generates overly optimistic coveragepercentage predictions. For the surface sce-nario, RMSDs of up to 25% are shown inthe region around 39° N 73° W, and thewarm salty intrusion observed on theMODAS data coincides with a second peakin the northeastern section of the graph.Overall the ASW scenario shows RMSDsthat are similar to the ASUW scenario, theonly difference being that the values are,on average, slightly smaller. The notableexception is the peak located at the topportion of the graph.

For the mid depth band the percentagecoverage RMS difference for the ASUW sce-nario is simply a scaled down version of theshallow depth band ASUW graph (Fig. 14).This makes a great deal of sense consideringthe fact that the coverage percentage distri-butions for the shallow and mid depthASUW scenarios were very similar. The realdifference is in the ASW scenario. The singleexceptional peak at the top of the previousgraph is gone and the observed differenceshave become much smaller. Most of theRMS differences for the mid depth ASWscenario do not exceed 10%. This is prob-ably due to nearly identical coverage per-

centage means from both data sets, and thetighter grouping of the GDEM data cover-age percentage predictions in the mid depthband ASW scenario. The RMSD values aresmall even in the areas where the tempera-ture and salinity differences were observedto be large, such as in the upper section ofthe graph.

The RMSD observed in the deep depthband scenarios are smaller than those of theshallow depth band, but similar in magni-tude to the mid depth band (Fig. 15). Forthe ASUW scenario the RMSD peaks nearthe northwestern corner of the AOI and thendecreases steadily in steps heading towardthe opposite corner. While the individual

RMSD values seen are not as large as someof the ones in the other depth bands, moreof the area has a non-negligible RMSD. Thecause of this can be seen from the percent-age coverage distribution for the deep depthASUW scenario.

The GDEM data results in values thatare almost all larger than the largestMODAS derived values. This overly opti-mistic prediction means that over a largeportion of the AOI, the RMSD is going tobe non-zero. The RMS difference in theASW scenario changes very little from themid depth band save for the fact that thevalues in the lower right corner are smaller.The coverage distributions for the deepASW scenario are similar to the ASUWcase, but the separation between the twomeans is not so pronounced. The result isa larger region where the RMSD is smallor zero.

Both of these graphs match the patternthat has so far been observed in the otherdepth bands. The ASUW scenario has thehigher RMS difference values, with areas ofboth high temperature and salinity differ-ences corresponding to peaks on the graphs.The RMS difference values also approachzero moving toward the top left or bottomright corners. Also, as depth increases, thedifference between the two data sets de-creases causing the difference between thecoverage percentages to decrease.

FIGURE 13RMSD for shallow depth band coverage: left panel for ASUW scenario and right panel for ASW scenario.

FIGURE 14RMSD for medium depth band coverage: left panel for ASUW scenario and right panel for ASW scenario.


ConclusionsBy looking at the RMSD in the tem-

perature and salinity fields generated fromthe GDEM and MODAS data, it is pos-sible to look for areas where the data differsignificantly. It is at these points that the dif-ference in the preset effectiveness should bethe greatest. This is observed for both sce-narios at all depth bands. The percentagecoverage is the most different at points whereboth the temperature and salinity RMS dif-ferences are large. This is especially true forthe shallow depth band where differencesof 25% are observed for both scenarios. It isof interest to note that even at the surfacethe RMS differences for the temperature andsalinity are never more than a few degrees orPSU. Even with only this slight increase inthe accuracy of the inputs, a large increasein the accuracy of the prediction of theweapon effectiveness occurred. This seemsto imply that the sensitivity of the presets tochanges in the inputs is quite high.

From the output distributions it becomesclear that the GDEM derived coverage per-centages indicate that weapon effectivenessshould vary not only in the horizontal butalso in the vertical. The implication is thatin some areas coverage will be very high andin others the coverage will be very poor, butthe tendency is for the coverage to be highfor any given area. The MODAS derivedpercentages reveal that the exact opposite is

true. The coverage will be consistent nomatter what the horizontal location or depthband. This is an important result since pre-diction of weapon effectiveness is vital tomission planning and execution. In this casean unrealistic expectation in the weaponseffectiveness would have resulted from theuse of the GDEM data to predict the cover-age percentages in the water column. TheMODAS data also would have given the userthe freedom to operate anywhere in the re-gion knowing that their weapon would func-tion about the same no matter the location.

The most obvious limitation of this workwas the limited data set. Any future workshould include data that covered a widernumber of areas and times. Areas of strongthermal and salinity contrast are of particu-lar interest. Various combinations of the userinputs into the WAPP should also be stud-ied. The effects of variables such as bottomtype and position (upslope/downslope) needto be addressed. Another avenue of study isthe determination of how the number ofaltimeters affects the accuracy of the out-puts. It has been determined that the pre-sets are sensitive to the addition of satellitedata. However, the effect of the number ofsatellite inputs still remains to be determined.Once this is done an optimal number of al-timeters can be determined based on mini-mizing cost and maximizing preset accuracy.

AcknowledgmentsThis work was jointly supported by the

Space and Naval Warfare System Commandand the Naval Postgraduate School. Theauthors would like to thank Charlie Barronat the Naval Oceanographic Office for pro-viding MODAS data set.

ReferencesChu, P.C., E. Gottshall and T.E.

Halwachs.1998. Environmental effects on

Naval warfare simulations. Institute of Joint

Warfare Analysis. Naval Postgraduate School.

Technical Report, NPS-IJWA-98-006. 33 pp.

Chu, P.C., S.K. Wells, S.D. Haeger, C.

Szczechowski and M. Carron. 1997. A

parametric model for the Yellow Sea thermal

variability. J Geophys Res. 102:5655-5668.

Chu, P.C., Q.Q. Wang and R.H. Bourke.

1999. A geometric model for Beaufort/

Chukchi Sea thermohaline structure. J Atmos

Oceanic Technol. 16:613-632.

Fox, D.N., W.J Teague, C.N Barron, M.R.

Carnes and C.M. Lee. 2002. The Modular

Ocean Data Assimilation System (MODAS).

J Atmos Oceanic Technol. 19:240-252.

Gandin, L.S. 1965. Objective analysis of

meteorological fields. Israel Program for

Scientific Translation. 242 pp.

Gottshall, E. 1997. Environmental Effects on

Naval warfare simulations. MS Thesis in

Physical Oceanography, Naval Postgraduate

School, (Monterey). 92 pp.

Jacobs, G.A., C.N. Barron, M.R. Carnes,

D.N. Fox, H.E. Hurlburt, P. Pistek, R.C.

Rhodes, W.J. Teague, J.P. Blaha, R. Crout,

O.M. Smedstad and K.R. Whitmer. 1999.

Naval Research Laboratory Report NRL/FR/

7320-99-9696. Navy Altimeter Data

Requirements. 25 pp.

Teague, W.J., M.J. Carron and P.J. Hogan.

1990. A Comparison between the Generalized

Digital Environmental Model and Levitus

Climatologies. J Geophys Res. 95:7167-7183.

FIGURE 15RMSD for deep depth band coverage: left panel for ASUW scenario and right panel for ASW scenario.


MI N T R O D U C T I O N

arine power plants are in a periodof intensive research and development. En-ergy conservation and manning are some ofthe factors contributing to escalating opera-tional cost and forcing rapid changes in longestablished design and operational practices.The unmanned engine rooms concept andautomated control systems of power plantsare being adopted by most shipping com-panies having large fleets of vessels. Thesenew and changing requirements have greatlyincreased the complexity of engine designto give optimum operating characteristicswithin given limits.

It is widely recognized that maintenance costis the most controllable element in ship opera-tion. The maintenance of power plants dependson the ease with which a plant can be strippeddown and repaired, the skill and number of thetechnical crew, and the cost of the components(Inozu and Karabakal, 1993). Hence, ship op-erators believe that the potential saving in anoptimized maintenance system can be substan-tial. The saving also depends on the mainte-nance technique and the level of interactionamong the working party. The use of condi-tion monitoring systems for the main enginesof ships and equipment on offshore rigs is nowvery common. It is now possible to transmit

information on marine equipment from com-puters in control rooms on board a ship or off-shore rig to control departments at shore baseusing an interactive system (Goto and Kaibara,1993). This has been made possible by the re-markable development of microelectronics andartificial intelligence. The economic use of thissystem depends on the size of the fleet and theskill of the technical staff.

This paper presents the merits and weak-nesses of three different maintenance policies:(1) a breakdown/replacement, (2) preventive(planned) only, and (3) optimal (condition-based and predictive) maintenance schemes.

Maintenance PolicyThe normal breakdown and planned

maintenance systems are based solely onsubjective judgement, which ensures thatbreakdowns are kept to a minimum. Themost economical system will be one that hasa better balance between the breakdown andthe planned maintenance systems.

Breakdown/Repair-onlyMaintenance Policy

A breakdown/replacement policy consid-ers a component that has suffered a major

A U T H O RK.D.H. Bob-ManuelRivers State University of Science

and TechnologyPort Harcourt, Nigeria

P A P E R

Use of Expert Systems for Optimum Maintenanceof Marine Power Plants

A B S T R A C TThe reliability and economical operation of marine power plants depend upon the

design quality, capability, and skill of the technical staff that operate the plant. The normalbreakdowns of marine machinery and the frequency of planned maintenance are basedmainly on the subjective judgement of the operators who ensure that such breakdownsare minimized. To achieve such objectives, an optimum maintenance goal must be adoptedusing various types of computer software for expert systems with high processing speed,which have been developed to aid fault or failure diagnosis. Such systems are at differentstages of application. In this paper, a typical expert system for condition monitoring,budgeting, and spare part management to enhance the optimum management of a marinepower plant is presented. The use of this technique with known models will substantiallyreduce downtime and fully utilize the technical crew onboard and ashore. From the author’sexperience in the management of ferries, there is an optimum amount of maintenanceeffort for any given condition.

failure and will cost a substantial amount torepair or replace. The repair or replacementof a component after a major breakdown ofa power plant can be defined as maintenancework which involves the rectification of afailed component that is brought back toworking condition by repairing or replacingthe damaged part. During the major repairsor replacement, checks and other minor re-pairs would be carried out. However, itwould not be very obvious if other compo-nents which are in fairly good working con-dition should be replaced or not at the sametime. A very crucial decision has to be madeif a component is worn to an extent that iteither becomes ineffective and causes troublein the near future or the part in questioncosts little to replace. A wise decision is toreplace the component immediately to avoidan unexpected major breakdown.

Replacement of Worn ComponentsDuring a major overhaul, replacement

and repair of failed or worn componentshave to be carried out by competent crew orgiven out on contract to the manufacturers.It is always a wise decision to allow the manu-facturers to install a major component toattract a guarantee on it. Whether to replace


Assuming that the fraction of the oldcomponent life that has undergone a certainperiod of usage is x

n, the remaining life of

the component at the time of replacement is(1 – x

n). The failure rate during this period

can be determined by the component de-sign factor and the operational condition. Anincreased rate of failure should be expectedduring the wear-out of the component.

Preventive (Planned)Maintenance Policy

In the preventive only or planned main-tenance policy, work is usually carried outto cut down the amount of downtime byobserving wear in the component and con-ducting condition monitoring to forestallunexpected breakdown. A preventive orplanned maintenance policy is also knownas a calendar-based or scheduled mainte-nance system. In this case, maintenance isprogrammed with an inspection systembased on either plant operating hours or cal-endar interval regardless of the duty cycle ofthe component or its condition. The main-tenance intervals are almost conservative asstipulated by the manufacturers. With thispolicy, wear in a component is frequentlyobserved and replacement made to forestallunexpected failure. The engineer may notforesee the actual service conditions and so

(s)he operates the policy with the unexpectedfailure that may occur due to design fault,which cannot be overruled.

A large portion of preventive mainte-nance can be planned to coincide with theperiod when a ship is in port or when re-pair work is being carried out on othercomponents. It could also be done whencomponents are opened up for survey byclassification society. However, the merit ofthe policy depends on the man-hours spentfor inspection and the reduction in the fre-quency of breakdown.

The risk of not keeping to a scheduledmaintenance period can be observed in Table1. It shows that most of the parametersmarked (*) are off specification. This was asa result of the tugboats not being taken infor normal planned maintenance at thespecified period due to operational demand.When eventually the engine in tugboat Cwas dismantled for servicing, it was foundthat the piston rings were excessively wornwith a burnt cylinder head gasket and thebig-end bearings were found to be worn.

One major drawback of this policy is thatit assumes that all engine hours are equal,yet factors such as running speed and load,fuel quality, ambient condition, etc. whichhave influence on the wear rate of the en-gine or accelerate the deterioration of the

FIGURE 1Weibull curve and probability of failure (Shields et al., 1995 )

a worn component immediately to avoidcatastrophic failure or defer it until the nextmaintenance schedule is usually a very diffi-cult decision to make. If the ship ownersdecide to wait until a significant portion ofthe component is worn out to save cost, theywill be exposed to the cost associated withdecreased performance and material degra-dation as well as unanticipated breakdown.This could put the safety of personnel andother equipment at risk in addition to thecost and replacement of the component. Forexample, if during a routine maintenanceand inspection, a component was found tobe cracked or worn, the possible decisionconcerning the component, which is stillserviceable, will be one of the following:■ Replace the component immediately.■ Wait until the component finally fails.■ Wait and replace the component at the

next scheduled maintenance.The cost of immediate replacement or

waiting until the component finally fails en-tails the cost of a new component, and labourin stripping the old component and fittingthe new one. The decision to wait until thenext scheduled maintenance imposes somelevel of uncertainty since the component mayfail before the scheduled period.

Remnant Life AssessmentUsing a normal theoretical Weibull dis-

tribution curve shown in Fig.1 can assess theuseful life remaining in an old componentbefore replacement. In this paper, the distri-bution will consider failure due to wear-outonly. The height of the Weibull curve is de-fined (Shields et al., 1995) as:

(1)where

β > 0 determines the shape of thedistribution.

η > 0 is the characteristic life of thecomponent.

t0

determines the origin of thedistribution time factor.


lubricating oil are not considered. However,excessive maintenance is not cost effectivesince engine downtime and the risk of ex-posure of the engine to maintenance-in-duced failure would increase.

Optimum Maintenance PolicyThe procedures proffered in break-

down/repair only or preventive (planned)maintenance policy cannot provide the so-lution to minimize overall maintenancecost. The policy which gives an optimalsolution is one with a specified degree ofplanned and breakdown/replacement main-tenance policies as illustrated in Fig.2 and

Use of an Expert System inFault Diagnosis

The conventional method of fault diag-nosis of a running engine is the detection ofthe change in performance using the senseof hearing, sound detection rod, lubricatingoil analysis, etc. The accuracy of detectiondepends upon the experts’ skill and experi-ence, hence the use of expert systems. Vi-bration measurement is the most widely usedmethod for fault diagnosis of rotating andreciprocating machineries. The principle isbased on structure-borne noise, which is ahigh frequency vibration caused by rotatingand reciprocating forces that occur at mi-croscopically small unsteady points. Thegeneral state of a plant will alter structure-borne noise characteristics as a result of de-terioration of the components.

Fig. 3 shows spectrums of vibration lev-els at different frequencies from a bearinghousing of an electricity generating plant(Bob-Manuel, 1999). The result can bescanned to computer memory for diagnosiswhen displayed on the visual display unit(VDU). Measurements of the vibration levelare usually taken by placing an accelerom-eter on the bearing housing at different po-sitions to find the maximum amplitude ofvibration level.

Frequency analysis of acoustic signals ob-tained for normal and faulty componentsduring operation as displayed in Fig. 4 canbe collected from the exhaust tail pipe to de-termine the waveform in different load andspeed conditions. Linear regression by meansof the least square method can be applied toeach region of the signal and the decay orthe rise of the amplitude approximated bystraight lines to determine the characteristictendency of the fault (Hikima et al., 1993).

In diagnosing a component that hasfailed using an expert system, the computerwill be programmed to make the judgement.In Fig. 5, the input variable would deter-mine the operational condition of the com-ponent. Comparing the actual and the ref-erence output variables is usually the start-ing point for diagnosis. However, therewould be an engineer–computer interactioni.e. the diagnosis of the failed component

TABLE 1Analysis of lubricating engine oil from 3 (three) tugboats using Spectrometric Oil Analysis Procedure(SOAP) (Chugbo, 1999)

PARAMETERS LUB-OIL SPEC. TUGBOAT A TUGBOAT B TUGBOAT C

Density @15 0.916 0.9253* 0.9026* 0.8887*

ˆC(kg/l)

Water Content (% vol.) Nil 0.40 0.15 —

Kinematic Viscosity 182.0 150.23* 125.23* 68.45*

@ 40ˆC (cst)

Kinematic Viscosity 14.4 33.49* 13.21* 8.95*

@ 100ˆC (cst)

Total acid No. 16.0 Too dark to observe 2.56 0.43

(Mg KOH/gr) colour change

Sulphated Ash % Wt 2.0 1.73 1.09 0.46

* Values are off specification

FIGURE 2Constituent and total maintenance cost for breakdown and planned maintenance policies (Shields et al., 1995)

is expected to result in the minimum costof maintenance and downtime. The deter-mination of the level of preventive (planned)maintenance requires mathematically ori-ented analysis and analytical ability. Theapplication in practice can be involved andcomplex requiring the use of competentskilled engineers. Another option is to in-troduce an integrated maintenance policythat capitalizes on the advantages of the op-timum policy while minimizing the disad-vantages of other policies earlier discussed(Haller and Kelleher, 1999). This policy hasbeen proven to identify component degra-dation before failure occurs.


being displayed on the VDU of the computerand showing the functional content of thecomponent. Possible causes of the failure andthe history of the unit will be displayed. Onthe diagnostic item menu, the results of themeasured values that indicate eminent fail-ure which are marked with codes would bedisplayed. The result and solution guidancecan be printed for detailed study. With thepresent communication system, if failure oc-curred on board a ship or offshore rig and thereplacement is required urgently, the result ofthe diagnosis can be sent directly to manage-ment at shore-base through the Internet.

The engine signature analysis in an ex-pert system involves recording various en-gine-operating signatures during loaded con-dition. This includes combustion pressure,cylinder vibration, lubricating oil analysis,oil and turbocharger boost pressure, oil andair filter pressures drops, excessive exhausttemperatures, etc. Component failure doesnot usually exhibit symptoms, which arereadily apparent in engine performance un-til significant damage has occurred. The au-thor observed on vibration analysis that en-gine performance did not deteriorate for sev-eral hours of operation, yet from vibration

FIGURE 3Computer display of vibration spectrum for diagnosis (Bob-Manuel, 1999)

FIGURE 4Spectrum of acoustic noise levels taken at exhaust pipes (Hikima et al., 1993)


signature analysis, fault was identified (Bob-Manuel, 1999). When such data are diag-nosed from a vibration test, the computercan be programmed to predict when cer-tain performances parameters or wear limitwill be exceeded.

Illustrated on the left side of Fig. 6 is anultrasonic signature taken when unexpectednoise occurred during compression andpower stroke of a four-stroke diesel engine.It was suspected that blow-by gases from thecylinder were responsible for the trends that

FIGURE 5Component model for monitoring and diagnosis

FIGURE 6Ultrasonic signature before and after cylinder liner replacement for a medium-speed diesel engine(Haller and Kelleher, 1999)

are circled. After the cylinder liner and pis-ton rings were changed, the blow-by gasesceased as confirmed by the signature shownon the right side of the figure. Subsequentinspection of the rings and liners confirmedthat excess liner wear caused the blow-by(Haller and Kelleher, 1999). It is importantto note from the pressure diagram that fir-ing pressure has not changed since the blow-by has not yet impaired performance, yetthe vibration signature analysis has identi-fied the excess wear.

Spare Part andStore Management

Expenditure on spare parts for marinepower plants accounts for a substantialamount of the vessel’s annual operating costs.One vital problem is that unavailability ofone relatively low cost component can pre-vent the sailing of a ship for a considerableperiod thereby increasing operational cost.Therefore, the effective management of spareparts in any maintenance scheme is of para-mount importance. Utilization patterns willvary because the demand may be fast or slow.

In most cases, an unexpected demandfor spare parts not in stock can be made butif enough notice is not given the cost arisingfrom downtime can be exorbitant. The pro-curement section should not be shortsighted,as it is often the case when considering thecost of spare parts. Factors such as invoicedcost, availability, quality, transportation, andpersonnel cost have to be taken into account.Correct decisions have to be made to enableparts to be supplied at the lowest possiblecost. The storekeeper faces the problem ofknowing when spare parts would be neededand the availability of funds to execute theorder. Hence, there is a need to define groupsof spares in stock and evolve codes for allequipment and spares. The problem ofwhich stock should be carried at any par-ticular time is complex and requires statis-tics of the utilization of spares. Standard soft-


ware for the management of spares exists andhas facilities for labeling individual spareparts for easy identification. It may also benecessary to scan essential drawings of sparesalong with part reference numbers for stor-age in the computer memory.

Budgeting forMaintenance Cost

Effective control of maintenance costinvolves adequate feedback by an efficientmanagement structure. Shore-based andshipboard management staffs require effec-tive coordination on budget control. A con-sultation process, which could lead to farreaching decisions, should be instituted. Forshipboard management in particular, headoffice has to be committed to the principlethat the technical crew onboard have anopportunity to contribute significantly to themaintenance policy, procedure, and regula-tion under which they operate. Such a sys-tem must be established before the con-trolled events begin to occur. All relevantevents must be reported and compared withthe approved plan and budget.

One of the basic essentials for preparinga meaningful account is a good ordering sys-tem. Such a system should enable trackingof cash flows and commitments of the bud-get to be kept. Budgeting should take ac-count of technical work that falls due at thescheduled planned maintenance period anda contingency allowance made for break-downs based on past experience. In an ex-pedient planning and budgeting system, thechief engineer onboard is expected to item-ize all work that needs to be done at a speci-fied time during the year, taking cognizanceof the annual survey period. (S)He does notdecide alone the time and place for dry-dock-ing and even the planned maintenance pe-riod can be affected by management deci-sion. The cost of the system can be appraisedon a yearly basis and updated. The reduc-tion in the cost of optimum maintenanceand the repair cost can take care of the costof the diagnosis system. Therefore, effectivecontrol of budgeting is a collective responsi-bility of shipboard and management staffs.

ConclusionThe economical operation of marine

vessels can be realized if there are ingeniouslyskilled manpower and reliable power plantsto minimize maintenance cost. The evolu-tion of computer technology with rapid de-velopment of expert systems and conditionmonitoring over the past years has enabledoptimal maintenance policies to be adoptedfor marine power plants. This has resultedin the reduction of maintenance cost ratherthan providing alarm signals only when acondition has exceeded set limit for safety.

An efficient diagnostic system has thepotential to aid ship operators to utilize a costeffective maintenance policy for marinepower plants and facilitates a clear presenta-tion and storage of crucial data. The imple-mentation of an expert system to achieveoptimal maintenance should be seen as achallenge and an opportunity for engineersto use technical and computer skills withcurrent scientific and management principles.

ReferencesBob-Manuel, K.D.H., H.I. Hart, and E. A.

Ogbonnaya. 1999. Computer-based condition

monitoring of an electricity generating plant.

I.Mar.E. Conference on Computers and Ships

- From Ship Design and Build, through

Automation and Management and on to

Support, pp. 87-95.

Chugbo, J.O. 1999. Project report on

condition monitoring of pusher tugs main

engines used for creek operations. Department

of Marine Engineering, Rivers State University

of Science & Technology, Port Harcourt,

Nigeria, p.11.

Haller, C.L. and E. P. Kelleher. 1999. Practical

integrated maintenance and diagnostic for

medium and slow speed diesel engines.

I.Mar.E. Conference on Computers and Ships

from Ship Design and Build, through

Automation and Management and on to

Support, pp. 103-128.

Hikima, T., T. Katagi, T. Naka, N. Ohyama

and T. Hashimoto. 1993. Diagnostic of marine

diesel engine faults by pattern recognition of

acoustic sound. Paper 16. ICMES 93 I.

Mar.E. Conference on Marine System Design

and Operation. pp.16.1-16.9.

Goto, T. and M. Kaibara. 1993. Remote

maintenance system by a programmed expert

knowledge network between ship and land.

Paper 29 ICMES 93, Conference on Marine

System Design and Operation. pp. 1- 29.11.

Inozu, B. N. and Karabakal. 1993. Replace-

ment and maintenance optimization of marine

system under budget constraints. Paper 30

ICMES 93, Conference on Marine system

Design and operation. pp. 1-30.7.

Shields, S., K. J. Sparshott and E. A. Cameron.

1995. Ship maintenance—a qualitative

approach. I.Mar.E. London: Marine Media

Management Ltd.


TI N T R O D U C T I O N

here are currently around 4000 or sostructures in the federally regulated offshorewaters of the Gulf of Mexico (GOM) asso-ciated with oil and gas production. The struc-tures vary widely according to function andconfiguration type and since 1947, when off-shore production in the Gulf first began,roughly 6,000 structures have been installedin the federal offshore waters and 2,000 struc-tures have been removed. On average, about100 or so structures are removed in theGOM per year, and over the past 10 years,the number of removals have ranged between79 and 168 (Kaiser et al, 2002).

Structures are installed to produce hy-drocarbons and when the time arrives thatthe cost to operate a structure (maintenance,operating personnel, transportation, fuel,etc.) outstrips the income from the hydro-carbons under production, the structure ex-ists as a liability instead of an asset. The eco-nomic lifetime of a structure can be extendedif the operating cost can be reduced (by di-vestment, unitization, or more efficient pro-duction practices) or hydrocarbon through-put increased (by investment). In the GOM,federal regulations require that all structureson a lease be removed within one year afterthe lease is terminated. Typically, a lease isterminated when production on the leaseceases, but if the operator intends to re-workwells or is pursuing activity on the lease, or

the lease contains an active pipeline, condi-tions may warrant granting an extension ofthe lease termination.

Decommissioning activities in the GOMare driven by economics and technologicalrequirements and governed by federal regu-lation. Decisions about when and how astructure is decommissioned involve issuesof environmental protection, safety, cost, andstrategic opportunity, and the factors thatinfluence the timing of removal as well asthe manner in which the structure is sev-ered from the seabed are complicated anddepend as much on the technical require-ments and cost as on the preferences estab-lished by the contractor and the schedulingof the operation.

Decommissioning occurs in stages andtypically over disjoint time frames as illus-trated in Figure 1. Greatly simplified, fol-lowing project engineering and cost assess-ment, federal and state regulatory permitsfor well plugging and abandonment, pipe-line abandonment, structure removal, andsite clearance verification must first be ob-tained. Wells are plugged and the facility isprepared for removal, including flushing andcleaning process components, installingpadeyes, etc. Pipelines are pigged and/orflushed riser-to-riser or riser-to-subsea tie-in, detached from the structure, capped, andnormally left in place. The topside facilitiesare prepared by removing all traces of hy-

A U T H O R SMark J. KaiserAllan G. PulsipherCenter for Energy Studies,Louisiana State University

Robert C. ByrdTwachtman Synder & Byrd, Inc.

P A P E R

The Science and Technology of NonexplosiveSeverance Techniques

A B S T R A C TA variety of cutting technology is used in support of decommissioning offshore struc-

tures in the Gulf of Mexico. The purpose of this paper is to describe the science and technol-ogy of nonexplosive severance techniques, and to examine their environmental, physical,safety, and activity requirements. Abrasive water jet, diamond wire, diver torch, mechanicalmethods, and sand cutters are the primary nonexplosive cutting techniques applied in theGulf of Mexico. The technology of nonexplosive removal techniques has not changed dra-matically over the past decade, but technological progress continues to be made, mostnotably in abrasive water jet and diamond wire technology. A review of each nonexplosivecutting technique will be described within and across each stage of decommissioning.

drocarbon, and then the deck is cut and re-moved, and the conductors and piles cut andpulled. Heavy lift vessels bring the jacketashore for recycling, sale, or scrap, or theoperator may participate in a reefing pro-gram. After the jacket has been removed, thesite is cleared with a trawling vessel or diversdeployed with scanning sonar, and thenclearance is verified with a trawler.

For readers requiring more specific infor-mation on the activities involved throughouta decommissioning project, the case studiesin Hakam and Thornton (2000), Kirby(1999), and Thornton (1989) are a good start-ing point. (See also Dodson, 2001, andTwachtman et al., 1995.) Detailed descrip-tions of each stage of the decommissioningprocess can be found in Byrd and Velazquez(2001), Manago and Williamson (1997),Pulsipher (1996), Twachtman et al. (2000),and National Research Council (1996).

The decommissioning of offshore struc-tures is often a severing intensive operation.Cutting is required throughout the structureabove and below the waterline and mudlineon braces, pipelines, risers, umbilicals, mani-folds, templates, guideposts, chains, deckequipment and modules. More significantcutting operations are required on elements thatare driven into the seafloor, such as multi-stringconductors, piling, skirt piling, and stubs whichneed to be cut at least 15 feet below the mud-line, pulled, and removed from the seabed.


A variety of technology exists to performseverance operations. These include abrasivewater jet, diamond wire, diver torch, explo-sive charges, mechanical methods, and sandcutters. For severing operations that occurabove the waterline, the cutting techniqueselected is usually dictated by the potentialfor an explosion. Cold cut methods are usedwhen the potential for an explosion exists;otherwise hot cuts are employed. Cuttingin the air zone is considered conventionalsince it involves methods that are regularlyused for dismantling onshore industrial fa-cilities. Below the waterline cutting is morespecialized. Divers can perform cuts onsimple elements such as braces and pipeline,and for shallow water structures such as cais-sons, diver-cutting is often the preferred sev-erance method. In deep water, remotelyoperated vehicles and automated diving sys-tems are sometimes deployed with abrasiveand diamond wire cutters and often withexplosive charges. Major cutting operationson conductors, piling, and stubs normallyemploy mechanical, abrasive water jet, andexplosive charges. Mechanical and explosivemethods are primarily used for conductorswith abrasive water jet and explosives pre-dominately used for pile severance.

A large number of factors are potentiallyinvolved in selecting the severance techniquefor a specific job with cost, safety, risk offailure, and technical feasibility the primaryfactors that are considered when alternativeoptions are available. Many different sever-ance operations are required during decom-missioning, and depending upon the job,more than one alternative may be available.Variables that drive the cost and risk associ-ated with a specific severance technique arenumerous and involve factors such as thelocation and nature of the site, sensitivity ofthe marine habitat, structural characteristics,the amount of pre-planning involved andthe schedule of the operation, salvage/reusedecisions of the operator, marine equipmentavailability, operator experience and prefer-ence, contractor experience and preference,the number of jobs the contractor is sched-uled to perform, the weather at the time ofthe procedure, and market conditions. Ingeneral, cutting techniques are expected to

FIGURE 1Decommissioning is a Severing Intensive Operation


be reliable, flexible, adaptable, safe, cost ef-fective and environmentally sensitive (Na-tional Research Council, 1996). If a cuttingtechnique fails with respect to one or moreof these factors, or if an operator has morethan one “bad experience” with a particularmethod, then chances are that the technol-ogy will gain neither in popularity or accep-tance among contractors.

The purpose of this paper is to reviewthe various nonexplosive cutting techniquesused in support of offshore decommission-ing, and to describe the technological, envi-ronmental, physical, safety, and activity re-quirements associated with each method.The outline of the paper is as follows. Insection 2, the cutting activities that occuracross the main stages of decommissioningare outlined, and in section 3, the scienceand technology of mechanical, abrasive wa-ter jet, diamond wire, and diver torch meth-ods is described. In section 4, the cuttingsystems and activity requirements associatedwith each method are discussed, and in sec-tion 5, the paper concludes with a brief sum-mary of the environmental and physicalimpact and safety issues associated with non-explosive cutting technology.

2. Decommissioning is Oftena Severing Intensive Operation

The basic aim of an offshore platformdecommissioning project is to render all wellspermanently safe and remove surface/seabedsigns of production activity. A site should bereturned to such a state as to allow the use ofthe site by other marine users, such as com-mercial fishermen and shrimpers. Cuttingoperations occur throughout each stage ofdecommissioning except the first (permitting)and last (site clearance and verification) stage.

2.1. Well Plugging and AbandonmentA well abandonment program is carried

out by injecting cement plugs downhole toseal the wellbore to secure it from future leak-age. The purpose of plug and abandonment(P&A) is to destroy the permeability withinthe formation and stabilize the wellbore andits associated annuli until geologic forces canre-establish the natural barriers that existed

before the well was drilled. Techniques as-sociated with P&A are based on industryexperience, research, and conformance withregulatory standards and requirements(Englehardt et al., 2001; Manago andWilliamson, 1997). Federal regulationsspecify the minimum requirements thatmust be performed in P&A operations.

A traditional approach begins by “kill-ing” the well with drilling fluids heavyenough to contain any open formation pres-sures. The Christmas tree is then removedand replaced by a blowout preventer throughwhich the production tubing is removed.Cement is placed across the open perfora-tions and squeezed into the formation to sealoff all production intervals and protect aqui-fers. The production casing is then cut andremoved above the top of the cement and acement plug positioned over the casing stub.The remaining casing strings are then cutand removed close to the surface and a ce-ment plug set across the casing stubs.

Mechanical methods of cutting and sandcutters are primarily associated with P&Aactivities. After wells are plugged and casingtubing cut and pulled, a sand cutter or me-chanical cutting tool may be run downholeto cut the conductors, or depending on thepreference of the operator/contractor andconfiguration of the platform, abrasive or ex-plosive severance methods may be contracted.In a typical mechanical operation, the tubingand production casing is first cut using a jetcutter—a small explosive blast that utilizesless than 5 pounds of explosive—and thenthe strings are cut using a mechanical cutter.The general philosophy during decommis-sioning is to get as much cutting done as pos-sible off the critical work path and before thearrival of the derrick barge if the activity canbe performed in a cost effective manner.

All well conductors and casings are re-quired to be removed to a depth of at least15 feet below the mudline, or to a depthapproved by the District Supervisor. TheDistrict Supervisor may approve an alternateremoval depth if (1) the wellhead or casingwould not become an obstruction to otherusers of the seafloor or area, and geotechnicaland other information demonstrate that ero-sional processes capable of exposing the ob-

struction are not expected; (2) the use ofdivers and seafloor stability pose safety con-cerns; or (3) the water depth is greater than800 m (2,624 ft). The requirement for re-moving deepwater subsea wellheads or otherobstructions may be reduced or eliminatedwhen, in the opinion of the District Super-visor, the wellheads would not constitute ahazard to other users of the seafloor.

2.2. Topside Equipment andDeck Preparation

Topside preparation and deck removalis made with cold and hot cuts. Cold cutsare generally made with pneumatic saws,diamond wire methods or abrasive tech-niques. Hot cuts—torch cutting and arcgouging—are used to cut steel when thereis no risk of explosion. Arc gouging, essen-tially an arc welder, is used to remove weldsbetween steel connections. Diamond wiremethods have occasionally been employedin the GOM to cut the deck from the jacket.

2.3. Jacket PreparationSeveral severing methods are used below

the waterline. Underwater burning torcheswork on the same principle as an arc-gouger,where a burning rod, usually magnesium, isarced with the member to be cut. Cuts madeto the jacket bracing and trimming, flowlines,umbilicals, and manifolds are typically per-formed with divers using burning torches, hy-draulic saws, or abrasive technologies. Inter-mediate cuts may be required to separate thejacket into vertical sections if the lift weightsexceed the capacity of the derrick barge.

2.4. Pipeline AbandonmentFederal regulations allow decommis-

sioned OCS pipelines to be left in placewhen they do not constitute a hazard tonavigation, commercial fishing, or other usesof the OCS. Pipelines will generally be re-moved offshore through the surf zone andcapped. Onshore pipelines may be removedcompletely, or some sections may be aban-doned in place if they transition through asensitive environment. The pipeline end sea-ward of the surf zone is capped with a steelcap and jetted 3 feet below the mudline.Most pipelines in the GOM are abandoned


in place after cleaning, cutting, capping andburying the ends.

The methodology for cutting a pipelinedepends on the manner the pipeline is to berecovered. The protective coatings typical ofmost pipeline sections must first be removedin order to cut the pipe with an arc torch. If apipeline crosses or is adjacent to an “active”pipeline, chances are it will not be disturbeddue to the potential damage that could resultif complications arise in the removal. Dia-mond wire methods, abrasive water jet, andpneumatic saws deployed with diver or ROVhave been used to cut pipeline.

2.5. Pile and Conductor SeveringPile and conductor severing is the most

critical and typically the most expensive ofall the severance operations required on thestructure with direct cost generally fallingbetween 1-3% of the total cost to decom-mission a structure (Kaiser et al., 2003). Theindirect cost of pile and conductor cutting,primarily the expected cost of failure to cut,is an important criteria in selecting a sever-ance method. Piles are steel tubes weldedtogether and driven through the legs of thejacket and into the seabed to provide stabil-ity to the structure, while conductors con-duct the oil and gas from the reservoir tothe surface. Piles and conductors must becut and removed 15 feet below the mudlineunless a special waiver is granted.

Conductor severing and recovery may becompleted as part of well plugging and aban-donment activities unless the platform con-figuration, equipment availability or sched-uling of the activities prevent the operation.Conductors are cut and pulled, if possible,early in the decommissioning process toavoid delay when the barge is on-site. De-pending on the number of structures to bedecommissioned, the type of structure andthe sequencing of the activities, a small spreadmay be sent to pre-cut the conductors. Thissaves derrick barge time if the conductorsare successfully severed, but also costs addi-tional money to dispatch the cutting crewand necessary support vessels. To verify acomplete cut, a jacking spread may be usedto lift the conductor after the severing at-tempt. To jack the conductors (“prove” the

cut), the platform must have the structuralcapacity to provide a point to jack againstand have a crane large enough to set the cut-ter, jacks, and load spreading beams. Me-chanical casing cutters and abrasive water jet(AWJ) cutters can be used to perform thecut if a crane is available on the platform forthe deployment of the tool. With a derrickbarge on-site, mechanical and AWJ cuttersare rarely deployed due to the time-consum-ing and inefficient nature of the operation.

The physical characteristics that describepiles and conductors are also important sincethey determine the technical feasibility ofseverance options. Conductors are config-ured in various diameters and wall thicknessand are characterized by the number of in-ner casing strings, the location of the stringsrelative to the conductor (eccentric vs. con-centric), and the application of grout withinthe annuli. Grouted annuli are usually easierto cut than annuli with voids since voidsdissipate the energy/focus of the abrasive andexplosive cutting mechanisms. Conductorsare usually cut with mechanical or explosivecharges. Mechanical methods are appliedduring P&A activity and if conductors arecut when the barge is on-site, then explosivecharges will probably be employed.

To sever jacket legs and piles, abrasivecutters and explosive techniques are effec-tive. Cutting piles is usually a much simpleroperation than conductor cutting, and insuch cases, AWJ cutting may be used with aderrick barge spread. In principle, mechani-cal cutting could be used to cut piling, butin practice it is rarely used because piles areonly open when a barge is on-site, and witha barge on-site, mechanical cutting is nei-ther a cost-effective nor efficient way to sever.Explosives are deployed down the piling andbelow the mudline while abrasive cutters canbe deployed internally or mounted externallyif the soil is excavated from around the out-side of the piling. Obstructions within thepile will necessitate additional operation ordeployment of an external cutter. Internalcutting is usually the preferred approach withwater jet technology since it does not requirethe use of divers to set up the system or soiljetting operations to access the required cut-ting depth below the mudline.

Cutting the piles and conductors is themost critical and important part of a decom-missioning project since if the piles and con-ductors are not cut properly, a potentiallydangerous condition could arise during thelift. The cuts on jacket members, piles andconductors must be “clean” and “complete”to allow for a safe operation. A dangeroussituation occurs when an element is not com-pletely cut (lease “hangers”) and “lets go”after the crane vessel has applied a signifi-cant pulling force.

3. The Science & Technologyof Nonexplosive RemovalMethods

For the most part, the resources requiredin decommissioning involve standard,readily available technology and tools whichhave been available for some time. Mechani-cal pipe cutters and diver torches are roughlythe same today as they were ten years ago,and while AWJ and diamond wire applica-tions have seen a moderate increase in thefrequency of usage, a variety of factors con-tinue to limit their application. The physi-cal limitations associated with AWJ systems(e.g., water depth, reliability) are significantlybetter today than they were a decade ago,and although the routine application of dia-mond wire methods is still several years away,the technology has made strides due to prod-uct development and the steady influx ofnew contractors into the GOM. The fol-lowing discussion can be considered an up-date of the National Research Council’s 1996report on cutting techniques (NRC, 1996).

3.1. Mechanical MethodsCutting mechanisms that use hydrauli-

cally actuated, carbide-tipped tungstenblades to mill through tubular structures arecalled mechanical cutters. Figure 2 shows aschematic of this type of system. The me-chanical casing cutter is perhaps the oldestmethod for cutting well conductors. Thecasing cutter is deployed on a drill pipe stringand lowered into an open pile or well. Thecutting tool has 3 blades that fold up againstthe drill pipe. When hydraulic pressure isapplied to the tool, the blades are forced


outward as the tool is rotated by a powerswivel. The carbide-tipped blades cutthrough the strings of the well while cen-tralizers on the tool keep it concentric in-side the tubular member. Drillers watch thepressure to determine when the cut is com-plete and cut indication can be made afterthe tool is recovered by observing the marksof penetration of the blades (Manago andWilliamson, 1997).

Mechanical cutters are frequently usedfor cutting shallow-water, small-diametercaissons with individual wells and well pro-tector platforms with vertical piles(Pulsipher, 1996; NRC, 1996). Mechanicalcutting is rarely used in conjunction with aderrick barge spread, however, since the op-eration is time-consuming and inefficientand rig-up and rig-down time may be con-siderable. After wells are plugged and casing

tubing cut and pulled (see Fanguy, 2001),the contractor may run a mechanical cut-ting tool (or sand cutter) downhole to cutthe conductors, or depending on the prefer-ence of the operator and configuration ofthe platform, may subcontract for abrasivewater jet or explosive severance methods.

A number of limitations are associatedwith mechanical cutting. For conductorswith casing string that is not cemented, lat-eral movement of the string may cause un-even cutting of the next casing. If strings arepulled after each cut, lifting equipment isrequired which adds to the time to removeand reinstall the tool. For cemented strings,trips in and out of the well may be requiredto replace worn blades, which add to thetime to complete the cut. Realignment of apartial cut after re-entry is problematic andeccentricity of the casing strings may resultin incomplete cuts forcing the deploymentof divers to perform the operation. Mechani-cal cutting is also problematic for tubularmembers at a batter (angle). To cut pilingwith mechanical cutters, the piling must beopen at the surface to accommodate thepower swivel. Thus, the deck of the plat-form must be removed prior to the opera-tion using a derrick barge, and after the deckis removed, it is highly unlikely for a bargeto stay on-site when the mechanical cuttersoperate. Remobilizing a derrick barge, how-ever, is usually not an option and would rep-resent a significant cost increase in the op-eration. Mechanical cutting is thereforerarely used for piling.

3.2. Abrasive MethodsMechanisms that inject cutting materi-

als into a water jet and abrasively wear awaysteel/concrete are called abrasive cutters.Abrasive technology has a long history ofapplication in industrial and manufacturingprocesses, and has been used in shipyardsfor many years. Several different systems ofabrasive cutters exist.

Abrasive cutters can be classified as:(1) Low pressure/high volume systems

(sand\cutters), or(2) High pressure/low volume systems (AWJ).

Cutters that use sand or slag mixed withwater at low pressure (4000-10,000 psi) and

FIGURE 2Schematic of a Mechanical Cutting System(Courtesy of Hydrodynamic Cutting Systems)


high volume (80-100 gal/min) are calledsand cutters, while cutters that use garnetinjected at the nozzle at high pressure(50,000-70,000 psi) and low volume (50-80 gal/min) are commonly referred to asabrasive jet cutters (NRC, 1996). The abra-sive provides the force for cutting and is in-troduced at the cutting nozzle and sent downa hose with air pressure or through a water-based solution. The abrasives typically usedare garnet and copper slag.

Sand cutters use a turning mechanism(or power swivel) like a mechanical cutter.The power swivel is connected to the top ofan open pile and as the drill string turns, thecutting nozzle cuts the pile through the abra-sive action of the water jet. Abrasive jet cut-ters produce a jet of water mixed with gar-net under high pressure and directed througha diamond orifice.

The minimum inside diameter that canbe accessed with abrasive cutters is approxi-mately 7 inches, and beyond 200-250 feet,some of the abrasive cutting technology em-ployed in the GOM is not effective. Im-provements to the systems over the past de-cade, especially with the influx of North Seatechnology, has allowed abrasive cutters towork in deeper waters than in previous years.Figure 3 shows a cutting tool intended foruse in conductors or small piles. Figure 4shows an AWJ tool capable of cutting pilesand caissons to 72 inches. Air delivery sys-tems are limited to shallow water application,while systems with a fluid delivery have beenused in water depths exceeding 600 feet (Bran-don et al, 2000). Abrasive cutting has alsobeen deployed by ROVs to depths exceeding1,000 feet. Casing strings that are eccentricand with void areas remain problematic sincethe void dampens the energy of the water jetand may cause an incomplete cut. (See Fig-ure 5 for a concentric cross-section).

There also exists the problem of verify-ing that the cut has been made when usingan internal abrasive cutter. Unlike explosives,the conductor or pile does not drop, con-firming that the cut was successful. With anabrasive tool, the width of the cut is smalland when combined with the soil friction, avisual response does not occur. To verify thecut, the conductor is pulled with either the

FIGURE 3Abrasive Water Jet Cutting Tool for Conductors and Small Piles(Courtesy of Circle Technical Services)

FIGURE 4Abrasive Water Jet Cutting Tool for Piles or Caissons from 30 to 72 inches Diameter(Courtesy of Circle Technical Services)

FIGURE 5Grounded Conductor Cross-section, Concentric


platform crane or hydraulic jacks, and thelift force must overcome the conductorweight and the soil friction. For an unsuc-cessful cut, the abrasive cutting tool is eitherre-deployed to make another complete runor explosives are used to complete the cut.

3.3. Diamond Wire MethodsA diamond wire cutting system uses a

diamond embedded wire on a chain saw-like mechanism to cut steel, concrete, orcomposite material above and below thewaterline. A diamond embedded wire isveered onto hydraulically driven pulleys re-sembling a band saw and mounted on aframe. The system can be configured to cutvirtually any structural component and isnot limited by size, material, or water depthas long as the cutting tool can be fixed tothe cut member. Diamond wire has beenused to cut caissons, conductors, risers, andpipeline. Diamond wire cutting has beenused since the early 1990’s in the North,Adriatic, and Red Seas; but in the GOM,diamond wire has only been applied on afew jobs. Figures 6 and 7 show diamond wiretools for different applications.

The cutting machine is hydraulicallyclamped or manually strapped to the struc-ture, and a surface-activated motor activatesthe tool. The diamond wire is driven at highspeeds and depending on the material andthickness, wire speeds are maintained to pro-duce the cut. Even under large axial com-pressive loads, tubular members can be cutwith diamond wire, and one of its strengthslies in its ability to cut large wall section thick-ness (Brandon, 2000). The operator moni-tors the progression of the cut and makesadjustments at the surface to improve theefficiency of the machine.

3.4. Diver Torch MethodsUnderwater diver cutting is virtually the

same as land-based cutting but the torchused is somewhat different. In underwaterarc cutting, an outside jet of oxygen andcompressed air is needed to keep the waterfrom the vicinity of the metal being cut. Atube around the torch tip uses air and gaspressure to create a gas pocket. This will in-duce an extremely high rate of heat at the

FIGURE 6Diamond Wire Cutting System Applied to a 72 inch Deck Leg on the Surface(Courtesy of CUT USA, Inc.)

FIGURE 7Diamond Wire Cutting System Deployed from a ROV for use in Pipeline or Small Member Cutting(Courtesy of CUT USA, Inc.)


work area since water dispels heat muchfaster than air. As the water depth of the cutincreases, higher air pressure is required toform the gas pocket (DOE, 1994).

Underwater cutting can also be accom-plished with an oxy-hydrogen torch. Hydro-gen is typically used instead of acetylenebecause of the greater pressure required inmaking cuts at increased depths. Oxyacety-lene may be used up to 25 feet while depthsgreater than 25 feet require the use of hy-drogen gas (DOE, 1994). Underwater cut-ting is generally limited to caissons, pilings,bracing, or other structural components, butnot wells. In shallow water and for simplestructures such as caissons, diving is some-times the preferred method.

4. Nonexplosive CuttingSystems and ActivityRequirements

4.1. Mechanical SystemsA mechanical cutting system requires a

tool to be lowered into an open pile or wellwith a crane or drill rig. If the cutting tool isoperated by a drilling rig, diesel-fired enginesdrive generators which provide electricalpower to motors, which rotate the turntable,which turn the drill string, which mills thetubular element. In addition, a water pumpcapable of up to 5000 psi pressure providesthe force to keep the mechanical blades ex-tended as the cutting progresses. If a drillingrig is not used, the rotary table is replacedby a power swivel, which is driven by a hy-draulic power pack. The independentlydriven cutting tool does not approach therig-based tool in cutting capacity, however,and thus may take a considerably longerperiod of time to cut. Mechanical cuttinggenerally requires at least three dedicatedpersonnel, although this is not easy to de-fine, since a drilling rig requires significantlymore people to function, and an indepen-dent operation would also require signifi-cantly more personnel to be self support-ing. The mechanical cutting operation isgenerally only conducted from a platformwithout an attending derrick barge, or froma drilling rig.

4.2. Abrasive Water Jet SystemsA standard abrasive water jet unit con-

sists of a cutting tool or manipulator to con-trol the positioning and movement of thenozzle, the abrasive mixing or dispensingunit, high pressure water pump(s) and hy-draulic power unit, control panels and cutmonitoring systems. The total weight of theAWJ system may range from 5-15 tons andhave a footprint of 200-400 ft. Several dif-ferent AWJ systems are commercially avail-able with prices ranging from $250,000-$500,000 for a complete system.

In a conventional internal pile cuttingoperation, the cutting tool is lowered intothe pile from a wire line winch (deploymentframe) or by a construction vessel crane. Thearms of the tool’s centralizing system stabi-lize the tool and the cutting nozzle is posi-tioned against the pile wall. A diesel-drivenwater pump supplies the high pressure wa-ter stream to the cutting nozzle and the pres-sure required is determined by the cut pa-rameters (e.g., wall thickness, cut configura-tion, abrasive mixing system, etc.). The cut-ting speed, direction of travel, and nozzleposition is controlled and monitored by theoperator at the surface control station (Bran-don, 2000). External cutting operations onlegs, piles, and brace members are carried outusing diver or ROV installed tracks. Subseavideo equipment, lights, and audio systemsfor cut observation and monitoring are com-mon for both internal and external cutting.

The surface personnel required for 12hour operations are generally two operatorsand two roustabouts. External underwaterAWJ systems need to be placed either bydivers or ROVs. The operation can be sup-ported from any work platform that has suf-ficient lifting capabilities; i.e., derrick barge,platform with a capable crane, lift boat, etc.

4.3. Diamond Wire SystemsDiamond wire cutting systems are typi-

cally composed of a clamping frame, cut-ting frame with wire drive pulleys and mo-tors, wire feeding system, wire tensioningsystem, cut wedging system, underwaterpower unit, umbilical assembly, and dia-mond wire cable (Brandon, 2000). Thepower to the system can be provided from

the surface, by means of a dedicated subseapower pack, or by a work-class ROV powerunit. Monitoring of the cutting progress isprovided by video cameras mounted on themachine frame, ROV, or by divers from asafe distance. The cutting machine is hydrau-lically clamped or manually strapped to thestructure, and a drive mechanism is eitherremotely controlled by an operator at thesurface or configured for automatic opera-tion by an ROV or diver.

4.4. Diver Torch SystemsArc torches for underwater cutting are

produced in a variety of types and forms andare constructed to connect to oxygen-airpressure sources. Electrodes may be carbonor metal and they are usually hollow in or-der to introduce a jet of oxygen into themolten crater surrounding the arc. The cur-rent practice is to use direct current for un-derwater cutting and welding.

The torch used in underwater cutting is afully insulated celluloid underwater cuttingtorch that utilizes the electric arc-oxygen cut-ting process using a tubular steel-covered, in-sulated, and waterproofed electrode. It uti-lizes the twist type collect for gripping theelectrode and includes an oxygen valve leverand connections for attaching the weldinglead and an oxygen hose. The arc is strucknormally and compressed oxygen or air is fedthrough the electrode center hole to providecutting. The burning electrode tip is shieldedfrom the surrounding water by the rapidlyexpanding gas from the combustion process.

5. Environmental andSafety Issues

5.1. Environmental andPhysical Impact

Energy is required to do work and all cut-ting operations require the expenditure ofenergy. As work is performed, energy is trans-ferred and transformed which may have animpact on the ocean environment where theoperations are performed. The power require-ments of a cutting spread are approximatelythe same as a small offshore fishing vessel (lessthan 200 horsepower, or 150 kW), but un-


like the typical sport fishing vessel, the cut-ting spread is fully self-contained with nomarine discharges. Nonexplosive cuttingmethods do not create the impulse andshockwave-induced effects which accompanyexplosive detonation and are therefore con-sidered to be an ecological and environmen-tally sensitive severance method. Environ-mental and physical impact data of nonex-plosive methods are quite limited in the aca-demic and trade literature and no record ofnegative environmental impact for nonexplo-sive cutting methods has been found.

In mechanical, abrasive water jet, and dia-mond wire removals, diesel fueled mechani-cal systems are employed in the operationwhich result in vibrations, the emissions ofCO

2 and other gases to the atmosphere, and,

potentially, low frequency sound waves intothe ocean environment. Abrasive water jetcutting involves using sea water and garnetor copper slag (grit), and so there is the ques-tion of the impact of the fluid and garnet onthe marine environment. Since the fluid in-volved in abrasive cutting is water and thegarnet is essentially inert, the environmentalimpact is believed to be inconsequential.Garnet is an inert rock material that posesno environmental consequences that havebeen reported. The level of copper presentin the slag is very low and there are currentlyno restrictions on its use or reported envi-ronmental issues. The noise level of the su-personic cutting jet is safe for divers and isnot considered harmful to marine life. Thedirect products of the processes are water,metal cuttings, and abrasive grit particles.

5.2. Safety IssuesOffshore oil and gas operations involve

a number of distinct phases—exploration,development, production, and decommis-sioning—and present a continuing risk ofaccident and injury to the personnel involvedin the operations. Drilling operations involvemoving heavy equipment into place (e.g.,pulling or hauling pipe) and the continualadjustment of controls and rotary equip-ment. Production operations involve themaintenance of process equipment as wellas activities associated with changingflowrates and reservoir depletion. Develop-

ment and decommissioning activities involvethe lifting and moving of heavy loads andnumerous other manual tasks such as rig-ging and welding. Decommissioning alsooften involves significant cutting operationsabove and below the waterline.

Drilling, installation, production, anddecommissioning operations are all person-nel intensive, but the exposure time involvedwith drilling and production operations areseveral orders-of-magnitude greater than withdecommissioning activities, and so if all op-erations in the offshore environment are as-sumed to be “equally hazardous,” we wouldexpect no significant safety issues to be asso-ciated with decommissioning projects sincethe time for a possible occurrence is so small,and indeed this is the case. Injuries and acci-dents that may occur on decommissioningare difficult to reliably detect relative to theexposure time involved in the activity.

On a drilling facility the crew size con-sists of about 20 people per 12-hour shift,while on a production platform, the crewsize varies with the number of wells and thecomplexity of the equipment (NRC, 1990).More than half the structures in the GOMare unmanned and serviced from a centralplatform with 20 or fewer people. In theWestern GOM, where gas fields are widelyscattered and platforms smaller, crew sizesalso tend to be smaller (2-10 people). Theaverage crew size on platforms that havemore wells per platform and more equip-ment than average, are expected to havelarger crew sizes.

In decommissioning operations, thenumber of personnel required on the job isdetermined by the size of the equipmentused. A small decommissioning project ona single platform in shallow water may re-quire 14-20 personnel and 3-7 days to op-erate the marine equipment spread. A mod-erately sized project with multiple platformsin shallow water may require 35-50 person-nel spread out over 30-45 days. A deep wa-ter decommissioning project with largeequipment may require in excess of 100-200personnel over a number of months.

All GOM leaseholders are required tonotify MMS of all serious accidents, anydeath or serious injury, and all fires, explo-

sions, or losses of well control connected withany activities or operations on the lease. Thisdata is reported to MMS and processed dur-ing each calendar year. An event refers to areported happening that may involve morethan one incident. An incident refers to acategory of accident that occurred duringan event. From 1995-2000, 80 percent ofthe reported events occurred during devel-opment/production activities and 20 percentoccurred during exploration activities (NRC,1990). The breakdown of incidents accord-ing to welding/cutting-related and crane-related incidents can be found in NRC,1990. Welding and cutting operationscaused no deaths in the GOM, but they didcause injury and accidents causing fire.

The basic safety issues with respect tomechanical, abrasive, and diamond wirecutting methods are somewhat comparable.Mechanical cutting tools and safety precau-tions are familiar to any drilling crew. Theabrasive water jet system involves high pres-sure hydraulics but the cutting spread areais considered a restricted work zone withsafety barriers and warning signs posted. Thecutting manipulators and hydraulic powerunits incorporate high pressures rangingfrom 5,000 psi (350 bar) to 50,000 psi(3,500 bar). The tools, hoses, winches orpower unit could cause injury if damagedor mishandled. The diamond wire methodsmay require a diver to be deployed whichalso presents special risks.

AcknowledgementsMany industry and government person-

nel provided generously of their time andexpertise for this study. We would especiallylike to thank Sim Courville and Jeff Cole,Hydrodynamic Cutting Services, and AlyHakam, ChevronTexaco. Nick Jones, OilStates MCS; Svein Solversen, Norse Cuttingand Abandonment; Michael Leska, Supe-rior Energy Services; Jeff Steele, RodrigueConsultants, Inc.; Tommy Broussard, JeffChilds, and Vicki Zatarian, Minerals Man-agement Service, also provided critical in-formation and useful feedback for this study.

This paper was prepared on behalf ofthe U.S. Department of the Interior, Min-erals Management Service, Gulf of Mexico


OCS region, and has not been technicallyreviewed by the MMS. The opinions, find-ings, conclusions, or recommendations ex-pressed in this paper are those of the authors,and do not necessarily reflect the views ofthe Minerals Management Service. Fund-ing for this research was provided throughthe U.S. Department of the Interior, Min-erals Management Service.

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TI N T R O D U C T I O N

he mission of deep submergence re-search vehicles built to date—such as“SHINKAI 2000,” “SHINKAI 6500,”“Alvin,” “Nautile,” and others—has been toprovide a means of enabling researchers tosafely access and directly observe the deepocean at a time when it was difficult for aman to venture to the deep seafloor. In thepast few years, the above-mentioned pur-pose has been realized, and it is now notunusual to explore the deep ocean bottomat depths of several thousands of meters.(Busby Associates, 1990; Rona, 1999-2000).

On the other hand, the needs for inves-tigation and research in the deep ocean con-tinue to increase. Looking ahead 10 to 20years, it is obvious that those needs will be-come more complicated and more advanced.(Walsh, 1998; Morr, 2001; Jones, 2001;Sagalevitch, 1997 & 2001). The increasedlevel of demand for investigation and re-search expected will be satisfied neither quan-titatively nor qualitatively with the few deepsubmergence research vehicles that are cur-rently available in the world.

When we study manned submersiblesneeds for the future, we should not neglectthe role of unmanned vehicles such as re-motely operated vehicles (ROVs) and au-

tonomous underwater vehicles (AUVs),which utilize highly developed sensors andremote sensing technologies. Today, success-ful operations and investigations are beingachieved with such unmanned vehicles. Fa-vorable opinions for development of deepocean scientific research systems using un-manned vehicles are growing. More produc-tive operations will be accomplished in thefuture as more effective and efficient un-manned vehicles are developed.

However, man is still important. Innatural science field studies, when mangoes down in situ into the deep ocean en-vironment he fully utilizes the “humansensor,”—i.e. the five sensory organs:“looking at with the eyes,” “listening to withthe ears,” and “feeling with the body.”Man’s presence will continue to be an im-portant element for expanding ideas andgenerating innovative knowledge and hy-potheses, along with establishing effectiveoperating procedures for the use of un-manned vehicles. It is considered thatmanned deep submergence research ve-hicles will remain essential tools as well asa central component in future develop-ment and use of deep ocean scientific re-search systems.

A U T H O R SDan OhnoJapan Deep Sea Technology Association

Yozo ShibataKawasaki Shipbuilding Corporation

Hisao TezukaMitsubishi Heavy Industries, Ltd.

Hideyuki MorihanaTokai University

Ryuichiro SekiJapan Marine Science and Technology Center

P A P E R

A Design Study of Manned Deep SubmergenceResearch Vehicles in Japan

A B S T R A C TThis paper covers the results of a design study recently completed in Japan on manned

submergence research vehicles equipped with Autonomous Underwater Vehicles (AUVs)and/or Remotely Operated Vehicles (ROVs). The primary features and general overview ofthe vehicle designs are described, and some of the major items to be examined in eachstudy are introduced.

At the outset of this study, the opinions of many domestic scientists and scholarswere collected in order to identify the most important subjects of future scientific re-search in the deep ocean.

This study was carried out by the “ad hoc Committee” organized by the Japan DeepSea Technology Association.

Present and future areas of deep oceanscientific research are interdisciplinary andglobal. Though they are too numerous tolist fully here, they span such earth studiesfields as:■ The atmosphere and oceans■ Studies of the correlation between fluid

movement and seabed movement on thedeep ocean floor

■ Earthquake prediction■ Chemosynthetic ecosystems on the deep

ocean floor■ Overall earth scientific studies focusing

on geophysics phenomena from abiological perspectiveTo do this work it has become neces-

sary to carry out wide range, three-dimen-sional, and simultaneous measurements.The nature of scientific observation itselfhas been changed; consequently it will benecessary to ensure that new manned sub-mergence vehicle designs respond to suchchanges. Manned submersible develop-ment should not remain on the peripheryof conventional research concepts andmethods. To bring them to the forefront,it will be necessary to introduce new con-cepts in design and technology.


To address this situation, an “ad hocCommittee” organized in the Japan DeepSea Technology Association first itemized theneeds for future deep ocean scientific re-search, then studied the design of manneddeep submergence research vehicles.

Prof. H. Morihana exercised overallcontrol of the study, and was joined by twocompanies, Kawasaki Shipbuilding Corpo-ration and Mitsubishi Heavy Industries,Ltd., representing manufacturers ofmanned deep submergence research ve-hicles in Japan.

Development and building of mannedsubmergence vehicles for future deep oceanscientific research will be an enterprise ofnational importance. It must be actively pro-moted for the noble purposes of contribut-ing to mankind’s well-being today and toensure prosperity of the future as interna-tional collaboration advances ocean exploi-tation technologies.

The Needs for Future DeepOcean Scientific Research

In recent years, the requirements of deepocean scientific research have led to increas-ingly larger areas to be investigated while themesh of investigations has become finer andfiner, and the depths have become deeperand deeper.

Scientific research in the deep ocean is arecent branch of wide-ranging marine re-search, and has been made possible by newlyevolving technologies. In the deep seas thescientist ventures into an unlimited treasurehouse of knowledge; it is truly a voyage intothe unknown (JAMSTEC, 2002).

In this regard, efforts to study the needsfor scientific research in the deep ocean overthe next 10–20 years will be critical for thedevelopment of both manned submergencevehicles and AUV/ROV systems for futuredeep ocean scientific research.

The Japan Marine Science and Technol-ogy Center (JAMSTEC) requested the Ja-pan Deep Sea Technology Association toundertake an “Investigation and study forthe outlook of deep ocean scientific researchfor the 21st century.” The study was doneduring fiscal years 1999 –2000.

The Association accomplished the inves-tigation and study by organizing an expertcommittee comprised of members selectedfrom wide-ranging fields covering marinegeophysics, chemistry, and biology in Japan.Seven themes shown in Table 1 were selectedas key fundamental items for new deep oceanscientific research.

Studies for Future Deep OceanScientific Research Systems

For the success of future deep oceanscientific research in the 21st century, it will benecessary to clearly ascertain the needs and speci-fications of that research and to design mannedsubmergence vehicles together with unmannedsystems that will satisfy the scientific needs.

As mentioned earlier, the areas of theocean to be surveyed should include the in-termediate layer, deep layer, seafloor, andsub-seafloor. Therefore, the submersible re-search systems must be able to functionthroughout broad, three-dimensional areas.

Some of the capabilities for investigationand observation that will be required fromthis system are multiple points simultaneousmeasurements, online observation, and re-peat observation through a network. Thesystem should be equipped with functionssuch as observation capabilities on the sea-floor, a means to collect and transfer the datastored in the observation facilities, and theability to freely move the observation facili-ties from point to point.

Future deep ocean scientific researchwork will require new manned deep sub-mergence research vehicles to incorporateunconventional features that will advanceexisting concepts of this kind of technology.It is critical not only to adopt emerging tech-nologies that are currently undeveloped butalso to seek development of ultramodernoriginal technologies that are far out of therealm of conventional technologies(Allmendinger, 1990).

It is also necessary for submersible op-erational capabilities to be greatly improved.For example, endurance times of existingmanned deep submergence research vehiclesare too short: 5 hours on the seafloor forNautile (maximum operating depth 6000

m); 10 hours submerged for Alvin (max.operating depth 4500 m), and maximum of9 hours underwater cruising (with 3 hourson the seafloor) for SHINKAI 6500 (max.operating depth 6500 m). Such short mis-sion times result in inefficient operations re-quiring multiple dives with repeated launch-ing/recovery from the support ship in orderto cover the wide range necessary to meetthe needs for investigation and observation.

One of the major limitations of deepsubmersibles is on-board power. Existingtypes of batteries will not provide the neededlong duration mission times. In recent years,however, fuel cells have attracted attentionas a power source, and they may be expectedto significantly extend the underwater op-erating time of manned deep submergenceresearch vehicles.

It is also important to consider mannedsubmersible operations equipped with AUV/ROV in order to achieve wider observationsand include many more items of investiga-tion within a limited period. For these pur-poses, it will be necessary to study the func-tions to control and manipulate AUVs/ROVs remotely from manned vehicles.

There are numerous other items to beconsidered and studied to improve mannedsubmersible capabilities. Better instrumen-tation, sensors and sampling devices; morecapable and powerful manipulators; ad-vanced imaging systems, and higher powerexternal lighting systems are examples ofthese items. It is also an important objec-tive to provide the capabilities for precisionas well as heavy work in the deep ocean, assuch needs are required in the future. Also,it is important to improve abilities for in situ(direct) observations, the most essential ca-pability of manned deep submersibles, byrearranging the position, increasing the num-ber, and expanding the size of the viewportsto permit a greater viewing area from vari-ous points in the pressure hull.

When designing improvements formanned deep submergence research vehiclesit is important to pay sufficient attention tothe opinions and experiences of all operatorsof manned deep submersibles that have beenused for oceanographic research. Special con-sideration should be given to JAMSTEC’s


experiences with “Shinkai 6500” and “Shinkai2000” (Takagawa, 1995).

An optimum design study of mannedsubmergence vehicles for future deep oceanscientific research should be carried out basedupon all of the above-mentioned consider-ations (Brown et al., 2000).

Studying Results for NextGeneration MannedSubmergence Vehicles forDeep Ocean Scientific Research

In selecting the characteristics formanned submergence vehicles for futuredeep ocean scientific research, the operatingdepth and time which will be required to

meet the needs for scientific research men-tioned above were finalized first. These aresummarized in Figure 1, which shows re-quired operating depths varying widely be-cause needs for scientific research are di-verse, and the operating depths overlap ac-cording to the various research themes.

Furthermore, maximum times on theseafloor, or undersea cruising times, are alsovary corresponding to the operating depths.Since designing manned deep submergenceresearch vehicles that meet all these requiredconditions (depth and time) involves verydifficult technical issues, it could be antici-pated this could require some trade-offs, suchas a cutback of the functions, and produc-ing a vehicle that is inconvenient to use.

Therefore, after examining thoroughly boththe functions to be provided to meet theneeds of the scientific research, and the tech-nical problems encountered in achievingthem, it has been decided to provide severalplans for manned submergence vehicles thathave different maximum operating depthsand maximum cruising times.

The manned submergence vehicles un-der consideration at this time are of fivedepth classes:(1) 11000 m (full depth)(2) 6500 m(3) 4000 m(4) 2000 m(5) 500 m

Study itemIntegrated studies of thedeep environment in theocean plate subduction zone

Integrated crustal studies bywhole mid-oceanic ridgessurvey

Global dynamics studies

Integrated deep sea lifeenvironmental studies

Development studies of deepsea survey. direct-connectingsocial and economicactivities

Deep seafloor carbon cyclesstudiesDevelopment studies ofexplorative techniques onunderground biospherebeneath the deep seafloor

ContentsStudies are aimed to understand the following phenomena:■ plate motion in the trench region■ crustal deformation, active fault activities and submarine

landslide occurrence■ distribution and evolution for the ecosystem in the ultra abyssal

zone, the bottom layer flow and water seeping fluxSurveying mid-oceanic ridges of the whole earth withhigh accuracy, studies are aimed to understandthe following phenomena:■ distribution of hydrothermal vents■ submarine volcanic activity■ crustal deformation■ ocean floor spreading processStudies are aimed to understand global dynamics of the deepsea environment; monitoring plate motion, seismic activities,volcanic activities, crustal deformation, deep current dynamicsand ecosystem changes of deep seafloor.

Investigating deep sea ecosystem throughout intermediatelayer, deep layer, seafloor and under seafloor, studies are aimedto understand life evolution, oceanic environmental changes toprotect global ecosystem.Studies are aimed to develop deep sea survey techniquescorresponding to mineral and energy resources survey andsampling, CO2 management and rescue for important deep seaaccidents etc.

Studies are aimed to determine global physical-chemical fluxon boundary layer between seawater and deep seafloor.Studies are aimed to develop innovative deep sea exploitationtechniques for resolving ecosystem of under seafloor biosphereand discovering new species of deep sea microorganisms etc.

Main observation and measuring item■ geomorphology and geological structure (by using precise

survey instrument, and ultra abyssal online network system)■ pore water seeping (by using vehicle and seafloor observatory)■ crustal deformation (by setting datum point and using vehicle)■ observation of benthos■ sampling the drilling core■ geomorphology, geomagnetic and gravimetric data■ CTD■ sea water composition etc.(by repeat observation with high

solution)

■ seismic wave■ crustal strain■ pressure■ temperature (by using integrated deep sea floor monitoring

system and borehole measuring system)■ deep sea microorganism (by long term deep sea environment

monitoring and sampling)■ deep sea organisms (by continuous observation and

sampling specimen)■ geomorphology and geological structure■ heat flow■ water seeping■ magnetic and gravimetric data■ benthos■ drilling core samples■ hydrothermal flux (by using hydrothermal event monitoring

system on and under seafloor long-term monitoring system)■ drilling core sampling technology (by using a non-contamination

type drilling machine for surface layer of deep seafloor)■ deep sea environmental monitoring technology

TABLE 1Fundamental items for new deep ocean scientific research


TABLE 2Results of conceptual designs of submergence vehicles

Principal Items of SubmersiblesMax. operating depth(1) Dimensions (L×B×H)(2) Weight in air(3) Cruising speed(4) Navigation range (surface)(5) Bottom operating time(6) Crew(7) Pressure hull(8) Power source

Max. operating depth(1) Dimensions (L×B×H)(2) Weight in air(3) Cruising speed(4) Navigation range (surface)(5) Bottom operating time(6) Crew(7) Pressure hull(8) Power source




11,000m (Full depth)11.7 × 2.7 × 3.5 m36 t1.0 kt (Max. 3.0 kt)¯¯¯¯3 hours2 (1 pilot)1 sphere, 1.9m i.d., Ti-alloyLi-ion secondary batteries

6,500m12.0 × 2.7 × 3.4 m38 t1.0 kt (Max. 3.0 kt)¯¯¯¯21 hours3 (2 pilot)Intersecting 2 spheres, 2.0m i.d., Ti-alloyLi-ion secondary batteries

4,000m13.5 × 5.5 × 4.8 m72 t2.0 kt (Max. 3.0 kt)¯¯¯¯92 hours4 (2 pilot)Intersecting 3 spheres, 2.5m i.d., Ti-alloyLi-ion secondary batteries

2,000m30.0 × 5.5 × 8.8 m300 t4.0 kt (Surface 10 kt)4,500 NM7 days (168 hours)8 (Max. 16)1 cylinder, 3.9m i.d., Ti-alloyLi-ion secondary batteries,&Diesel electric generator500m37.0 × 5.5 × 8.8 m350 t4.0 kt (Surface 10 kt)4,500 NM14 days (336 hours)8 (Max. 16)1 cylinder, 3.9m i.d., High tensile steelFuel cell & Diesel electric generator

Major Features ofSubmersible System(1) Capable of full depth underwater

operation(2) Efficient ascent / descent speed

by minimizing fluid resistance(3) High performance automatic

maneuvering / 1 pilot cont. system(4) Large capacity of payload(5) Wide range of vision for TV camera

& view ports(6) High efficient buoyancy material(1) Extended operating time on the

sea floor compared with “Shinkai6500” (3h→21h)

(2) Cross over ocean ridges(3) Reserved inner utility space by

2 spheres(4) Capable of AUV / ROV operation

(Launch, recovery & supervising)(5) Large capacity of payload(6) Wide range of vision for TV

camera & view ports(1) Extended operating time on the

sea floor compared with theexisting submersibles

(2) Cross over ocean ridges(3) Reserved inner utility space by

3 spheres(4) Capable of AUV / ROV operation

(Launch, recovery & supervising)(5) Large capacity of payload(6) Wide range of vision for TV

camera & view ports(1) Capable of ocean-going /no need

of support ship(2) Long term & large area(3) Comfortable large space, habitable

for a long term operation(4) Introduction of various

automatic systems(5) Capable of AUV/ROV operation

(Launch, recovery & supervising)(6) Very large capacity of payload(1) Capable of ocean-going /no need

of support ship(2) Long term & large area(3) Extended operating time on the

sea floor by using FC-AIP system(4) Comfortable large space habitable

for a long term operation(5) Capable of AUV/ROV operation

(Launch, recovery & supervising)(6) Very wide range of vision with

large acrylic spherical view port

Measuring/OperationCapabilities(1) Sampling of sea water & bottom

layer(2) Measurement of CTD, O2,

current, magnetism, etc.(3) Geological monitoring &

measurement of seafloor(4) Monitoring & sampling of bottom

organisms(5) Setting & recovering of

instruments(1) ~(5); Do.

(6) Research on the dangerouspoints /narrow courses byAUV/ROV

(1) ~(5); Do.


(1) ~(5); Do.


(1) ~(5); Do.


(1)

(2)

(3)

(4)

(5)


Design studies for planning each of thesevehicles were carried out. The characteris-tics of each system, their operational andmeasurement capabilities, and principal par-ticulars for each class of manned submer-gence vehicles are summarized in Table 2.The profiles of five types of submersibles areshown in Figs.2 (1)–(5).

In the planning of the five submergenceresearch vehicles, the most important itemsin each vehicle were studied. The major itemsare as follows.

■ Descending and ascending method.■ Reduction of vehicle weight and etc.(for

11000 m class)■ Study of battery capacity required for both

cruising speed and on site operation time.■ Study of two connecting spherical hulls,

and etc.(for 6500 m class)■ Comparison study of multiple intersecting

spheres and cylindrical hull, and etc.■ Study of underwater launching and re-

covery system from a support vessel, andetc. (for 4000 m class)

■ Study of weight and capacity of varioustypes of AIPs (Air Independent Powersystems), and corresponding studies ofnumbers of cruising days and distanceto be available under restricted weightand capacity.

■ Comparison study of secondary batterywith the AIPs , and etc.(for 500 m classand 2000 m class)Taking the following two items from the

above listing, the outline of the study resultsshall be introduced in the two sections below.■ Descending and ascending methods of

the full depth (11000 m class) manneddeep submergence research vehicle

■ Size of the submergence research vehiclewhen an AIP is incorporated in a 500 mclass manned deep submergence researchvehicle

Descending and Ascending Methodsof the 11000 m (Full depth) ClassManned Deep SubmergenceResearch Vehicle

The preliminary study concluded that thetime of one dive to the depth of 11000mwould be 10 hours. This includes three hourseach for descending and ascending whichwould require an average speed is 61.1m/min.This is approximately 1.4 times as fast as theaverage speed of 43.3m/min for descendingand ascending of “Shinkai 6500” (time fordescending and ascending to and from6500m depth is 2.5 hours respectively). Itrequires approximately 2 times the descend-ing force in order to increase the speed up toas much as 1.4 times faster. This speed is ob-tainable by increasing the weight of the steelballast for descending and ascending. How-ever, in order to minimize the total weight ofthe vehicle and to keep enough payload, ameans to keep the vehicle at an inclined atti-tude during descending and ascending wasstudied, instead of the conventional methodof keeping the vehicle at horizontal attitude.With the submersible pitched down there willbe less drag in an advancing direction com-pared to the drag in a vertical direction.

If the angle is too small when a vehicledescends and ascends at an inclined attitude,the kinetic energy is consumed in horizon-tal movement and the speed in the vertical

FIGURE 1The operating depth and time which will be required by scientific needs


FIGURES 2 (1) - (5): “The profiles of five vehicles”

FIGURE 2 (1)11,000m class (full depth) vehicle

FIGURE 2 (2)6,500m class vehicle





FIGURE 2 (5)500m class vehicle

direction becomes rather slower than thoseobtained at a horizontal attitude. From thesecircumstances, to increase the speed with aninclined attitude, the vehicle should take aconsiderably large trimmed angle and alsohave a small drag coefficient in the horizon-tal direction.

The study results for the effects of atrimmed angle on the speed of descending andascending with an inclined attitude are shownin Figure 3. Changes of speed of descendingand ascending against the trimmed angle areindicated with change of apparent drag coeffi-cient Cd

a, and the vertical axis of the illustra-

tion takes the ratio to drag coefficient Czo in

the case of descending and ascending in attackangle of 90 degrees (descending and ascend-ing in a vertical direction while keeping thevehicle horizontal). As shown in this illustra-tion, exceeding 20 degrees of trimmed angle,effectiveness in increasing speed could be ob-served; and around 30 degrees might be con-sidered as the most effective trimmed angle.

In addition, we observe that changingthe ratios of drag coefficients between anadvancing direction and a vertical direction

of the vehicle produces an improvement inspeed. When the ratio is 1:10, the apparentdrag coefficient at 30 degrees of trimmedangle becomes about half as low as that ofvertical descending and ascending, so thatthe effectiveness is significantly large. Asmaller drag coefficient causes reduction ofthe weight of the steel plate ballast to bestored on the vehicle, resulting in a reduc-tion of the overall weight of the vehicle. Inthe case of the full depth manned deep sub-mergence research vehicle examined in thisstudy, the above-mentioned descending andascending with an inclined attitude achievesa reduction of the weight of the steel plateballast to be stored by as much as about 1ton, and a reduction of overall vehicle weightby as much as about 1.4 tons.

Study of an AIP System for a500m Class Deep SubmergenceResearch Vehicle

For submersible vehicles to continue ac-tive sub-sea operations for many days, apower source such as an AIP system using afuel cell is considered an effective solution.

(Perry Jr, et al., 1990 ; Meyer, 1993 ;Baumert, 1993). This is based on the factthat naval submarines and submergence ve-hicles equipped with an AIP system using aStirling engine have already been put intoservice. As for fuel cell systems, it is reportedthat German submarines equipped with AIPsystems using fuel cells have been commis-sioned in 2004. (Strasser, 1995 ;Hammerschmidt, 2001 ; Hauschildt, 2001).Also smaller cells will become a better andmore practical type of AIP system in the nearfuture, as a result of the current state of theirtechnical development for use in automo-biles. Generally, AIP systems have compli-cated organization and heavy weight andrequire a large space, in comparison withconventional batteries.

Improved AIPs will bring the advantageof endurance to large sized submergencevehicles, such as the 500m class, over smallones. This section shows the results of thestudy of the required weight and volume ofan AIP system for use in a 500m class ve-hicle. In this study, to evaluate the effective-ness of the AIP system simply in compari-


son with the battery, we have calculated thenecessary weight and volume of both AIPsystem and battery for the same requiredperformances.

Table 3 shows the design conditions ofthe study with some of the values in the tablebeing estimated. For the AIP system, we haveassumed a PEFC (Polymer Electrolyte FuelCell) type fuel cell to be used, and for thebattery, a lithium-ion secondary batterywhich has the highest energy density of thepresently available ones. The performancesof the lithium-ion secondary battery areimproving every year and are expected to be

higher than the present ones several yearsfrom now. Therefore, the present perfor-mances and expected targeted ones for thefuture are both indicated. Since the fuel cellperformance is expected to be steadily im-proved, the target values in the future areindicated. As for the hydrogen supply, themethanol reforming method is selected fromamong potential ones expected to be devel-oped in the near future.

Figure 4 compares the weights (left) andvolume (right) of the lithium-ion second-ary battery and the PEFC-AIP system. Ac-cording to these results, it is apparent that

the AIP system is lighter than the lithium-ion secondary battery, but in volume, thereis little difference between the AIP systemand battery (target values).

Figure 5 shows the breakdown of weight(left) and volume (right) of the PEFC-AIPsystem. It is seen that more than 70 % ofthe weight is attributed to oxygen-relateditems such as liquefied oxygen (LOX),LOX-tank and cold box. To reduce the AIPsystem weight further, therefore, it will beespecially important to reduce the weightof the LOX-tank and cold box (throughuse of new materials, optimization of thestructure and required inner pressure ofLOX-tank, etc.), in addition to reducingoxygen consumption by improving thepower generation efficiency. In volumebreakdown it is also seen that oxygen-re-lated items, as with the weight breakdown,take up a greater percentage.

However the percentage covered bymethanol and pure water generation isgreater than in the case of weight break-down. To reduce the volume of AIP sys-tem, it is important to improve the powergeneration efficiency to reduce the quan-tity of methanol, pure water, etc., in addi-tion to taking the same means as in theweight reduction case.

On the assumption that a lithium-ionsecondary battery (target value) and PEFC-AIP system as studied above are installedin a 4 m diameter cylindrical hull as a bat-tery room and AIP room, respectively, wehave studied the weights and dimensionsof these rooms. The results are shown inFigure 6. Since the LOX-tank of the AIPsystem is installed outside of the hull, it isnot included in the required room lengthbut added separately in the total length(room length + LOX-tank length). Accord-ing to these room length results, when theendurance is short, the AIP room is longerthan the battery room. This is mainly be-cause in the AIP system, a diesel generatoris installed to obtain the surface speed ofabout 10 knots. Regarding the weight, thebattery room is far heavier than the AIProom. That seems to be caused by the lightweight of the LOX-tank that is designedfor a 5 MPa pressure tank.

FIGURE 3Effectiveness in improving speed for descending and ascending with inclined attitude


FIGURE 4Comparison in weight and volume between Li-ion battery and PEFC-AIP for 500m class vehicle

Required electric powerEndurance of submergencePower sourceOperational depthWeight energy ratioVolume energy ratioPower generation efficiency (Output)Power generation capacityWeight (package)Volume (package)Oxygen consumptionMethanol consumptionPure water generationCO2 generationType

Material Outer pressure vesselInner pressure vessel

Design pressure Outer pressure vesselInner pressure vessel

Material

Conditions40 kW(on running speed of about 4 knots)7 to 28 daysLithium-ion secondary battery or PEFC500 m150 Wh/kg (target value)100 Wh/kg (present value)300 Wh/lit. (target value)200 Wh/lit. (present value)50 % (target value)46 kW(Target: 6 kW for CO2 compressor)31 kg/kW67 lit./kW0.6 kg/kWh (target value)0.4 kg/kWh (target value)0.45 kg/kWh (target value)0.55 kg/kWh (target value)Double-hull horizontal cylindrical (Vacuum insulation betweenouter and inner pressure vessels)Titanium alloy9 % Ni-steel5 MPa5 MPaTitanium alloy

ItemsDeep submersible researchvehicle

Lithium-ion secondary battery

PEFC system(Fuel cell)

Liquefied oxygen tank

Buoyancy adjustment tank

TABLE 3Design conditions of AIP study


FIGURE 5Breakdown of weight and volume of PEFC-AIP system for 500m class vehicle

FIGURE 6Comparison in weight and length between Li-ion battery room and PEFC-AIP room for 500m class vehicle


Conclusions It has been fifteen years since “Shinkai

6500” was launched in 1989, providing theworld’s greatest depth capability for amanned submersible. During this same timeperiod remotely operated vehicles and au-tonomous unmanned vehicles were devel-oped worldwide and became available withadvanced controlling and sensing technolo-gies. Today a lot of investigations and op-erations in the deep sea are utilizing theseunmanned systems. However, it is still veryimportant that humans work in situ to di-rectly observe and act; this capability will benecessary at any time and in any period. Evenif simulation technologies are advanced inthe field of natural science, the necessity offieldwork will not be diminished.

Efficient and highly capable mannedsubmergence vehicles that are responsive tothe future needs of scientific research in thedeep ocean must be used in collaborationwith various kinds of unmanned vehicles.In summary, the study concludes thatmanned vehicles will continue to assume themost important role in the whole system.

The study team expects that there willbe lively discussions among scientists, sub-mergence vehicle operators, and engineerson the best means to support effective fu-ture deep sea scientific research using themanned deep submergence research vehicleconcepts described in this paper.

ReferencesAllmendinger, E. E. 1990. Submersible

Vehicle Systems Design. The Society of Naval

Architects and Marine Engineers.

Baumert, R. and Epp, D. 1993. Hydrogen

Storage for Fuel Cells Underwater Vehicles.

Proceedings of Oceans ’93 (Vol.II), pp. 166-171.

Brown, R. S., Foster, D. & Walden, B. 2000.

Manned Submersible Improvement Options –

Summary Report, WHOI. http://

www.marine.whoi.edu./ ships/Sea Cliff/report.htm.

Busby Associates. 1990. Undersea Vehicles

Directory—1990-91. Busby Associates, Inc.

Hammerschmidt, A. E. 2001. PEM Fuel Cells

– An Attractive Energy Source for AIP

Independent Propulsion Systems. Proceedings

of UDT 2001-EUROPE, Session 6c.

Hauschildt, P. 2001,. Hydrogen Storage and

Hydrogen Generation on Board Modern

Submarines. Proceedings of UDT 2001-

EUROPE, Session 6c.

Japan Marine Science and Technology Center

(JAMSTEC). 2002. Toward Life and the Whole

Earth—Ocean Science’s New Direction. The

30th Anniversary Commemorative Issue,

JAMSTEC.

Jones, T. N. 2002. The Investigation and

Excavation of a Deepwater Shipwreck in the

Gulf of Mexico. MTS Journal. 36(3):51-54.

Meyer, A. P. 1993. Development of Proton

Exchange Membrane Fuel Cells for Underwater

Applications. Proceedings of Oceans ‘93

(Vol.II), pp. 146-151.

Morr, B. 2001. Autonomous Submarines

Broadening Industry’s Horizons. Sea Technology

(Sep.), pp. 26-33.

Perry Jr., J. P., Alessi Jr, D. P., Misiaszek, S. M.

and Person, A. 1990. Application of a Proton

Exchange Membrane Fuel Cell (PEFC) to an

Existing, Man-Rated, Small Submarine.

Techno-Ocean ’90, pp. 543-551.

Rona, P. A. 1999-2000. Deep-Diving Manned

Submersibles. MTS Journal. 33(4):13-20.

Sagelevitch, A. M. 1997. 10 Years Anniversary

of Deep Manned Submersibles MIR-1 and

MIR-2. Proceedings of Oceans ’97, pp. 59-65.

Sagalevitch, A. M. 2001. Second Discovery of

the Bismarck Wreck. Sea Technology. (Dec.),

pp. 31-35.

Strasser, K. 1995. Air-Independent Propulsion

with PEM Fuel Cells. Proceedings of

SUBCON ’95, German Submarine Technol-

ogy, pp. 32-33.

Takagawa, S. 1995. Advanced Technology

Used in Shinkai 6500 and Full Ocean Depth

ROV Kaiko. MTS Journal. 29(3):15-25.

Walsh, D. 1998. Deep Diving for Fun and

Profit. Sea Technology (Dec.), pp. 47-52.


T monthly trends of salinity and temperaturedistribution at several stations for the sameperiod of time. Three years later, Eleuteriusand Beaugez (1979) presented a descriptionof the climatic hydrographic conditions inthe Mississippi Sound. It gave some estimatesof the distributions of several hydrologicalparameters (temperature, salinity, oxygen,etc.) at various depths and at the bottom,but it was based on a small number of sta-tions. Kjerfve (1983) collected and analyzedmeteorological data, fresh water discharge,tides, currents, and temperature and salin-ity data from several mooring sites for theperiod of April-October 1980.

All these studies were based on ratherscarce data available before NGLI and there-fore they cannot be used for validating anoperational numerical model of the area.NGLI surveys have provided a much largernumber of sampling locations for the pe-riod of 2 years, higher vertical resolution,more repeatable stations, and better geo-graphic positions of the stations than anyprevious hydrographic observations in theMississippi Bight. Based on NGLI data anopportunity presents itself to perform somereasonable quantitative estimates of spatialand temporal variability of temperature andsalinity in the area.

The purpose of this paper is to presentan analysis of NGLI temperature and salin-ity data aimed at the comparison of observed

A U T H O R SSergey VinogradovNadya VinogradovaVladimir KamenkovichDmitri NechaevDepartment of Marine Science,University of Southern Mississippi,Stennis Space Center

P A P E R

Temperature and Salinity Variabilityin the Mississippi Bight

A B S T R A C TConductivity-temperature-depth (CTD) profile data from five surveys performed by

the R/V Pelican in the Mississippi Bight in February, May, and November 1999; and Janu-ary-February and August-September 2000 have been analyzed. The data were collectedwithin the framework of the Northern Gulf of Mexico Littoral Initiative (NGLI). The analy-sis of the T-S diagrams demonstrated substantial seasonal changes. Some estimates ofthe spatial variability at different scales were suggested. The analysis of the T-S dataobtained at time-series stations revealed some interesting effects such as along-shelfintrusion of deep water into the coastal system and fine vertical T-S structures in shallowpasses between the barrier islands.

and simulated data in the area. No attemptshave been undertaken to determine the cir-culation in this area.

Oceanographic Observations

a. Data Acquisition, Processingand Editing

The measurement procedure for theCTD (conductivity-temperature-depth)profiler consists of lowering it to depth andraising it back to the surface. The seawaterproperties are measured during both lower-ing and raising, and the data sets obtainedby the sensors are called downcasts andupcasts, correspondingly. Two sensors in-stalled for both temperature and salinity re-sult in two data sets—primary and second-ary—so each CTD station consists of 4 datasets for both temperature and salinity.

Preliminary data processing was per-formed by the U. S. Naval OceanographicOffice. The editing of data that we have car-ried out was aimed at the creation of a spe-cial database useful for the assessment of amodel performance, rather than at the gen-eration of a universal database of all mea-sured data. First, a set of primary data hasbeen chosen for all stations. The analysis hasshown a better quality of upcast data in theupper layers (0-5m), compared to downcastdata, while both upcast and downcast data

I N T R O D U C T I O N he Northern Gulf of Mexico Littoral

Initiative (NGLI) is the most recent andcomprehensive study of the littoral zone ofthe Mississippi/Alabama coast, focusing onthe Mississippi Sound area. The goal ofNGLI was to develop a sustainednowcasting/forecasting system for the coastalareas suitable for coastal resource manage-ment (Asper et al., 2001). Starting in 1999,NGLI has gathered a unique and significantdatabase of hydrological observations thatlends itself to various statistical and variabil-ity analyses.

The area of the Mississippi Sound is2130 km2 and the mean low water depth isonly 3.0 m (Kjerfve, 1983). The series ofsandy barrier islands (including Cat, Ship,Horn, Petit Bois, and Dauphin Islands) sepa-rate the shallow coastal waters from theNorthern Gulf of Mexico. Fresh water in-flow comes directly from major rivers suchas the Pearl, Biloxi, and Pascagoula alongwith diffuse land drainage and small bay-ous, and indirectly from the MississippiRiver and Mobile River. Saline waters fromthe Gulf are transported through the passesand straits between barrier islands.

Some estimates of temperature and sa-linity variability were performed byEleuterius (1976a; 1976b) who suggestedpreliminary daily patterns of salinity distri-bution at various depths for the period fromJune1973 to February 1975 and determined


looked reliable in deeper layers at most sta-tions. A more homogeneous flow and lessbubbles around the sensing elements, and amore stable upward motion of the CTDrosette may be the determining factors of abetter quality of the upcasts. The data at thesurface (0m) appeared very unreliable whichis why they were not included in the data-base. Then the obvious outliers such as nega-tive or very high values of temperature andsalinity have been removed. No data filter-ing or smoothing has been performed.

A time-series group is a set of stationsdone at the same location for a period of upto 25 hours (diurnal cycle). Normally thesampling interval was 1 hour, with a fewexceptions. There are 7 time-series stationsin the February 1999 survey, 2 in May 1999,6 in November 1999, 4 in January-Febru-ary 2000, and 2 in the August-September2000 survey, for total of 21 time-series sta-tions (see Table 1).

A transect group is a sequence of stationsdone along some straight line. Most of theCTD stations were done within the Missis-sippi Sound, including short transects alongship channels off Pascagoula, Gulfport, andBiloxi. The transect along the ship channelin Mobile Bay was performed in all surveys(locations along the median of Mobile Bay,between the Mobile River delta and the Mo-bile Bay Pass; see maps on Figs 1.1a – 1.5a).Time-series groups were often done in or nearthe passes and straits of the Mississippi Soundor between Dauphin Island and Mobile Point.Offshore data consisted of long transects sea-ward of the barrier islands. The duration ofthe surveys ranged from 10 to 15 days.

b. General AnalysisTo estimate the total range of salinity and

temperature variations for the whole survey,T-S diagrams have been plotted. T-S dia-grams reproduce not only the hydrologicalpicture of the survey, but also allow a quali-tative estimation of the data variability.Figs.1.1a – 1.5a show the location of CTDstations in 5 cruises of the R/V Pelican. T-Sdiagrams of these surveys are shown inFigs.1.1b – 1.5b. The T-S diagram for eachsurvey includes both shallow and offshorestations, so it captures the variability on tem-

FIGURE 1Location of CTD stations and T-S diagrams

(1.2.b) T-S diagrams for May 1999 survey

(1.3a) Location of November 1999 CTD stations

(1.1a) Location of February 1999 CTD stations (1.1b) T-S diagrams for February 1999 survey

(1.2a) Location of May 1999 CTD stations

(1.3b) T-S diagrams for November 1999 survey

poral and spatial scales of the whole survey(10-15 days, coverage of more than 30,000km2). It allows the analysis of large-scale fea-tures of the whole Mississippi Bight, withthe separate consideration of the shallow anddeep water contributions. At the same time,

if needed, any particular water mass can beeasily ‘detached’ from the total T-S diagramfor examination on smaller scales.

The February 1999 T-S diagram(Fig.1.1b) shows that, in wintertime, theseaward waters are warmer but still saltier


change in direction of the temperature gra-dient (towards land). Large changes in theheating regime in the springtime lead tohigher variability of temperature values ascompared to the February 1999 data.

For the November 1999 survey(Fig.1.3a), a single mean T-S curve (mostconcentrated data) was considered. Thiscurve consists of two parts: a vertical groupof points and a set of points bulged downfrom the right side to the left (see Fig.1.3b).The latter reveals subsurface gradients ofboth salinity and temperature while theformer is caused by a sharp temperature gra-dient at depths from 60 m to 80-90 m. Thissharp gradient is presumably the effect ofupwelling along the shelf and shelf break.

The January-February 2000 survey(Fig.1.4a) has the largest number of stations(385). The T-S diagram (Fig.1.4b) representsa winter pattern where the seaward waterscan be warmer than the waters in the near-coast zone. Here we have two distinct T-Szones: a vertical group of points, correspond-ing to a substantial temperature gradient inthe 100–500 m layer, and two curves bulgeddown from the right side to the left. All T-Sgroups tend to 8º C temperature value—the surface value in the Mississippi Soundand the value in the deep continental slope.As compared to the February 1999 survey,the overall mean temperature of shallowcoastal zones decreased by 4-5º C. The vari-ability analysis shows that temperature varia-tions at the surface layer 0.5–8 m are thehighest among all processed surveys (at spa-tial scales more than 24 km). This is due tolarge differences in temperature (up to 10ºC) between cold coastal surface waters andwarmer Gulf waters.

The August-September 2000 survey(Fig.1.5a) includes 6 transects performedseaward of the barrier islands to depths asgreat as 480 m, the Mobile ship channeltransect, and observations within the Mis-sissippi Sound. It has been used for prelimi-nary assessment of the performance of theEstuarine and Coastal Ocean Model(ECOM) (Vinogradova et.al., 2004). Smallvariations in temperature and salinity val-ues from the mean vertical profiles have beenobserved in this survey. The average T-S

(1.5b) T-S diagrams for August/September 2000 survey

(1.4a) Location of January/February 2000 CTD stations (1.4b) T-S diagrams for January/February 2000 survey

(1.5a) Location of August/September 2000 CTD stations

CTD Surveys Total number Duration of Number of time- Number of Number ofof stations survey (days) series stations spatial groups transect groups

February 1999 245 13 7 4 5

May 1999 219 10 2 6 5

November 1999 312 14 6 6 4

January/February 2000 385 15 4 5 16

August/September 2000 178 15 2 3 7

Total: 1339 67 21 24 37

TABLE 1Synopsis of analyzed oceanographic data.

than coastal ones. The main curve on the T-S diagram bulging down from the right tothe left side reflects this fact. A smaller groupof data points builds up a secondary curvewith almost constant temperatures (e.g.,Pascagoula transect). A scattering of datapoints around the two distinct curves on theT-S diagram gives a clue about scales of tem-perature and salinity variability. Based on

such an analysis we conclude that salinity gra-dients persist while the variation of tempera-ture remains small. The T-S diagram for theMay 1999 survey (Fig.1.2b) reveals a latespring vertical distribution when the surfacewaters become warmer by 6-7º C than deeplayers. Again there are two T-S curves, butnow they both are bulged down from the leftcorner to the right, which corresponds to the


curve (Fig.1.5b) with a very small data scat-ter is readily seen on the T-S diagram. Thehorizontally aligned group of points corre-sponds to the river inflow (mostly MobileBay data) in shallow homogeneouslywarmed waters. The almost vertical groupof points represents the 50–480 m portionsof the Gulf transects where the temperaturemonotonically decreases with depth from30ºC to 7ºC at the bottom while salinityhas the mean value of about 36 (mean sa-linity of the Gulf of Mexico waters).

Spatial Variability withinthe Mississippi Bight

In this section, we estimate the variabil-ity of the T-S fields for different horizontalscales at various depth intervals and for dif-ferent surveys. A rather simple approach isused to obtain a preliminary estimate. Theamount of data available precludes the useof any sophisticated methods, like clustermethod (see, e.g., Hur et al., 1998).

Towards the objective we select specialgroups of stations. A group is suitable forspatial variability analysis if (1) it is not a

transect; (2) stations within a group are lo-cated in a region with similar bottom depths,current intensity, etc.; (3) the number of sta-tions is not too small (otherwise the statisti-cal methods would be inapplicable); and (4)the stations within a group should have beenperformed within a relatively short time pe-riod. All non-transect or non-anchoredgroups are considered as potential spatialgroups, and, if they satisfy the requirementsdescribed above, they were used in the analy-sis. The total number of selected spatialgroups is 24. The radius of the spatial groupis defined as a half of the distance betweenthe two most distant stations within thegroup. Fig.2a illustrates one example of spa-tial groups.

Estimation of spatial variability was per-formed by using the following procedure:1. The spatial radius was calculated for each

spatial group.2. The average values of temperature and

salinity were calculated within a groupfor each depth levels from 0.5 m to 8.0 m.This depth range is determined by thefact that most spatial groups are in shallowregions in the vicinity of barrier islands.

3. The standard deviations of temperatureand salinity (within a group) were cal-culated for each depth level from 0.5 mto 8.0 m.As a result, the plots shown in Figs. 2b and

2c have been constructed. These plots havethree major axes: the depth in meters; spatialradius in kilometers; and standard deviation,in ppt, for salinity and in ºC for temperature.

In general, the variability decreases withdepth and increases with spatial scale. Notethat there are pronounced sharp-gradientlayers for some salinity and temperature ver-tical profiles in the upper subsurface zone of2.5–6.0 m, which are caused by fresh waterinflow, diurnal variations, and vertical mix-ing (see Temporal Variability section for fur-ther discussion). Due to these gradients, thedeviation of salinity or temperature fromtheir mean values increases with depthwithin some spatial groups.

Thus the overall maximum salinity vari-ability is 8.0 ppt (February 1999 survey,spatial scale of about 22.7 km, 5.0 m depth),and the maximum temperature variabilityis 3.0 ºC (January-February 2000 survey,spatial scale of about 23.8 km, 1.0 m depth).

FIGURE 2(2a) The illustration of spatial group definition. This is group 17, February 1999 survey, performed betweenGulfport ship channel and Biloxi ship channel in the Mississippi Sound. Total duration (a time scale) of thisgroup is 5 hours 24 minutes. Spatial scale is determined by the radius of a circle that barely covers all stationsin the group. It is 8.83 km for this group, based on coordinates of stations 153 and 168, the most distant amongall stations in this group. Standard deviations versus spatial scale for (2b) salinity and (2c) temperature. Verticalbars on these plots represent standard deviations computed for each spatial group. It gives an estimate ofcharacteristic variability for a particular spatial scale, season, and depth associated with spatial groups.

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(2b)

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Seasonal trends are also seen on these twoplots. The winter surveys (February 1999,November 1999, and January-February2000) have similar high amplitudes of salin-ity deviations as compared to the May 1999and August 2000 surveys on equivalent spa-tial scales. At all spatial scales, the smallestvariations in temperature correspond to theAugust-September 2000 survey data whereasthe highest temperature deviations corre-spond to the January 2000 survey.

Temporal Variability in theMississippi Bight

A time-series group represents a set ofobservations performed at the same locationfor a period up to 25 hours with a samplingperiod from 30 min to 2.5 hours. The analy-sis based on these CTD stations gives infor-mation on the temporal variability of tem-perature and salinity fields for scales up tothe diurnal cycle. The total number of pro-cessed time-series groups is 20.

We use two types of temporal variabilityrepresentation. First, mean vertical tempera-ture and salinity profiles are plotted withhorizontal “error” bars equal to standarddeviations at the corresponding depth lev-els. Second, graphs of temperature and sa-linity values versus time are constructed atdifferent depths.

Time-series stations performed in No-vember 1999 at 50–90 m depths in the vi-cinity of the shelf break reveal significanttemperature drops in the near-bottom layer(Fig.3c). The upper layer (0–65 m) at sta-tion A with a total depth of 81 m is stronglyhomogeneous (25.5°C, 36.3 ppt, see Figs.3b and 3c). At 65 m, the temperature dropsdramatically while salinity increases slightly.Mean temperature and salinity at the bot-tom are 22.1° C and 36.4 ppt respectively.These gradients are stable on a diurnal timescale, with a slight change in the thicknessof the near-bottom layer.

The presence of a stable, significant tem-perature gradient indicates the intrusion ofanother water mass into the homogeneoussystem. The intruding water mass is muchcolder and slightly saltier than the local well-mixed system. Temperature changes at 60,

FIGURE 3Along-shelf intrusion. (3a) Location of 4 selected time-series stations. Diurnal mean vertical profiles and standarddeviations for salinity (3b) and temperature (3c) at 4 stations. Diurnal changes in temperature (3d) and salinity(3e) at 60, 75 and 80 m depths, station A.

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(3b) (3c)


(3d)

(3e)

FIGURE 3Along-shelf intrusion, continued.

75, and 80 m depth levels at station A(Fig.3d) clearly show a large amplitude fluc-tuation at 75 m around the mean value thatimplies a strong and stable source of thisintrusion. Similar bottom temperatures fordifferent locations (as seen in vertical pro-files of stations B, C, and D on Fig.3d) pos-sibly identify the same water mass. An along-shelf upwelling is assumed to be a source ofthis water intrusion.

Station B (Fig.3a) was performed at 51mdepth two days later than station A. It rep-resents similar characteristics of the near-bottom layer, with a little less intensity. Shal-low time-series station C (30 m depth) showsvery homogeneous profiles from surface tobottom while the station D done at 88 mreveals a more sophisticated, stair-like struc-ture for the temperature profile (Fig.3c).

The persistence of these gradients formore than two days, and the pronounceddirection and intensity of intrusion provethe stable character of this phenomenon.The geographical location of described sta-tions gives some indication of the horizon-tal scales of near-bottom intrusion. Datafrom this survey show the presence of a near-bottom water mass forming at about 40 mdepth in the areas open to the shelf break.

Time-series stations located in passes be-tween the barrier islands provide some in-teresting material for studying the tempera-ture and salinity vertical structure. The Feb-ruary 1999 survey reveals different types ofdiurnal variability in the vertical structureof both the salinity and temperature fields.

Station 02 (Fig. 4a) is located south ofMobile Bay, in the area of extensive freshwater outflow from Mobile Bay into the Gulfof Mexico. All temperature and salinity pro-files at this station (Fig. 4b) show the exist-ence of two distinct layers: lower (5–10 m)vertically homogeneous layer with nochanges in time and upper layer (0-5m)highly variable both in time and in depth.Salinity changes from 2 to 10 ppt at the sur-face, and, starting from 5 m, gradually in-creases with depth up to 35 ppt. Low sur-face values of salinity may be caused by in-tense fresh water transport from Mobile Bay.Temperature changes from 21 to 17.5° C atthe surface, while the subsurface vertical gra-

FIGURE 4Time-series stations located near passes and straits. (4a) Location of 3 selected time-series stations. Verticalprofiles of temperature and salinity observed at station 2 (4b), station 6 (4c) and station 14 (4d). Diurnalchanges in temperature and salinity at 3 characteristic depth levels: station 2 (4e), station 6 (4f) and station 14 (4g).

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dient at 2–3 m remains almost unchanged.Subsurface temperature gradients are devel-oped due to the tidal motion and diurnalwarming/cooling of the upper layer. Fig.4erepresents diurnal changes in temperatureand salinity at 1.0m, 3.0m and 9.0m depths.

Station 06 south of Horn Island Passrepresents another type of diurnal variabil-ity. There is no strong evidence of subsur-face temperature gradients (Fig. 4c); andsubsurface vertical salinity gradients are notas strong as at the previous location. Thisdifference can be explained by smaller trans-port out from the Mississippi Sound throughthis pass. Fig.4f shows diurnal changes oftemperature and salinity at 1.0 m, 3.0 mand 9.0 m depths.

Time-series station 14 located south ofCat Island Pass shows very small changes inboth salinity and temperature within 25 hours(Fig. 4d) and it could be considered almosthomogeneous in the vertical. Diurnal varia-tions of temperature and salinity at 1.0 m,3.0 m and 7.0 m depths are shown on Fig.4g.

DiscussionThe NGLI CTD database appears to be

useful for a preliminary study of the clima-tology of the Mississippi Sound. The com-parison of surveys performed over one yearfrom February of 1999 to January-Februaryof 2000 provides some material for studyingseasonal variability of temperature and salin-ity fields in the area. The comparison of Feb-ruary 1999 and January/February 2000 sur-veys have demonstrated a possibility of stronginterannual variability. The results of theanalysis are important for assessing the skillof hydrodynamic operational models of theregion (Vinogradova et al., 2004).

High diurnal variability has been dis-closed, based on the analysis of time-seriesstations. For the coastal waters, stratificationcan change dramatically within a day in someareas. In once vertically homogeneous waters,high subsurface vertical salinity gradients candevelop within a few hours and can also van-ish within a short time due to tidal advectionthrough passes between the barrier islands.

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FIGURE 4Time-series stations located near passes and straits, continued.

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(4d)


(4e)

Special diagrams have been suggested help-ful in estimating the spatial variability.

The late fall offshore stations located inthe vicinity of the shelf edge reveal stablenear-bottom vertical gradients in tempera-ture caused by some intensive intrusion of acolder water mass. We hypothesize thatalong-shelf upwelling causes this intrusionalthough additional data and further analy-sis are needed to validate this assumption.

AcknowledgementsThe authors are very grateful to John

Blaha, head of the NGLI project, for usefulsuggestions and to Carl Szczechowski for pro-viding us with initially processed data andmany helpful comments. The paper was sig-nificantly improved due to the detailed andhelpful guidelines provided by anonymousreviewers. This work was funded by the Com-mander, Naval Meteorology and Oceanog-raphy Command through N62306-01-D-BOO01-0002 to support the Northern Gulfof Mexico Littoral Initiative.


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ReferencesAsper V., J.P. Blaha, C. Szczechowski, C. Cumbee,

R. Willems, S. Lohrenz, D. Redalje, and A-R.

Diercks. 2001. The Northern Gulf Of Mexico

Littoral Initiative (NGLI): A Collaborative

Modeling, Monitoring, And Research Effort.

J Miss Acad Sci. 46(1):60.

Eleuterius, C. K. 1976a. Mississippi Sound

Salinity Distribution and Indicated Flow

Patterns. Technical Report. Mississippi-

Alabama Sea-Grant Publication 76-023.

Eleuterius, C. K. 1976b. Mississippi Sound

Temporal and Spatial Distribution of

Nutrients. Technical Report. Mississippi-

Alabama Sea-Grant Publication 76-024.

Eleuterius, C. K., and S. L. Beaugez. 1979.

Mississippi Sound, a Hydrographic and

Climatic Atlas. Technical Report. Mississippi-

Alabama Sea-Grant Publication 79-009, 135 pp.

Hur, H. B., G. A. Jacobs and W. J. Teague.

1998. Monthly Variations of Water Masses in

the Yellow and East China Seas, November 6,

1998. Journal of Oceanography, 55:171-184.

Kjerfve, B. 1983. Analysis and Synthesis of

Oceanographic Conditions in Mississippi

Sound, April Thru October 1980. Technical

Report. Army Corps of Engineers, Mobile

District, 438 pp.

Vinogradova, N., S. Vinogradov, D. Nechaev,

V. Kamenkovich, A. Blumberg, Q. Ahsan, and

H. Li. 2004. Validation of the Northern Gulf

of Mexico Littoral Initiative (NGLI) Model

Based on the Observed Temperature and

Salinity in the Mississippi Bight Shelf.

J Atmos Ocean Tech. (submitted)


As one of the tools to manage environ-mental problems created by the above men-tioned causes, interest in developing a capa-bility to provide short-term forecasts ofcoastal ocean conditions is now rapidly grow-ing. This is, however, a formidable task sincethe coastal oceans represent some of the mostchallenging marine environments for mod-eling in the world (Haidvogel andBeckmann, 1998). The time and space scalesof interest associated with short-term coastalcirculation may be as short as a few hoursand as small as a few tens of meters or less.Irregular coastlines and steep and variablebottom topography near the coast (and atthe shelf break) can create highly complexpatterns of flow. Circulation on the conti-nental shelf is primarily governed by factorssuch as winds, tides, buoyancy fluxes,throughflow ( i.e. the permanent and sea-sonal alongshelf currents), and cross-shelfforcing by basin scale processes, etc. (e.g.,Johnsen and Lynch, 1995). Within thisframework, many (but not all) coastal pro-cesses occur. Wind forcing produces bothsurface and internal waves, and contributes

A U T H O R SLaurence C. BreakerMoss Landing Marine Laboratories

Desiraju B.RaoEnvironmental Modeling Center,National Centers for EnvironmentalPrediction

John G.W. KelleyCoast Survey Development Laboratory,National Ocean Service

Ilya RivinBhavani BalasubramaniyanScience Applications International Corporation

P A P E R

Development of a Real-Time Regional Ocean ForecastSystem with Application to a Domain off theU.S. East Coast1

A B S T R A C TThis paper discusses the needs to establish a capability to provide real-time regional

ocean forecasts and the feasibility of producing them on an operational basis. Specifi-cally, the development of a Regional Ocean Forecast System using the Princeton OceanModel (POM) as a prototype and its application to the East Coast of the U.S. are pre-sented. The ocean forecasts are produced using surface forcing from the Eta model, theoperational mesoscale weather prediction model at the National Centers for Environmen-tal Prediction (NCEP). At present, the ocean forecast model, called the East Coast-Re-gional Ocean Forecast System (EC-ROFS) includes assimilation of sea surface tempera-tures from in situ and satellite data and sea surface height anomalies from satellite altim-eters. Examples of forecast products, their evaluation, problems that arose during thedevelopment of the system, and solutions to some of those problems are also discussed.Even though work is still in progress to improve the performance of EC-ROFS, it becameclear that the forecast products which are generated can be used by marine forecasters ifallowances for known model deficiencies are taken into account. The EC-ROFS becamefully operational at NCEP in March 2002, and is the first forecast system of its type tobecome operational in the civil sector of the United States.

to surface flow directly through wind drift,Ekman transport, and Stokes drift. Tidalforcing, in addition to the depth-indepen-dent barotropic processes, also includes in-ternal tides which are often generated at theshelf break (Wiseman et al., 1984). Coastalwaters are particularly sensitive to major at-mospheric events which may occur fre-quently (Brink et al., 1990). Fresh water dis-charge from various bays and estuaries alongthe coast add buoyancy fluxes which fur-ther complicate the water motions locally.Also, in coastal areas, water mass integritybreaks down and the property relationshipswhich characterize these water masses in thedeep ocean often do not apply in shallowcoastal areas where the effects of local mix-ing often destroy their coherent nature. Asnoted by Mooers (1976), however, the situ-ation is not hopeless since the circulation,although complex, is not simply an unstruc-tured, incoherent, noise-like turbulence, butrather can be interpreted (and thus modeled)in terms of (albeit many) simple processes.

I N T R O D U C T I O Nhe population of coastal regions around

the continental U.S. has increased dramati-cally over the past 60 years and is expectedto continue to increase in the foreseeablefuture. Over 50% of the U.S. populationnow resides along our coastlines. Populationsin a majority of coastal counties from Texasthrough North Carolina have increased al-most fivefold between 1950 and 1990(Pielke and Pielke, 1997). The greatest in-crease in population occurred in Floridawhere the increase was over 500%. By theyear 2025, nearly 75% of all Americans areexpected to be living and working in coastalareas (Hinrichsen, 1998). Such increases inhuman population are affecting the coastaloceans more profoundly and more rapidlythan is global climate change (Hay andJumars, 1999). The pollution problem dueto terrestrial, atmospheric, and in situ sourcescontinues to degrade the quality of coastalwaters surrounding the U.S. Over two tril-lion gallons of partially treated sewage plusmore than 2 million tons of chemical wastesare discharged into U.S. coastal waters eachyear (Hinrichsen, 1998). 1 OMB Contribution No. 206


Interest in the scientific and technicalchallenges involved in predicting the stateof the coastal ocean started with a series ofworkshops on coastal physical oceanogra-phy starting ca.1974. In particular, a work-shop was held in 1989 to determine systemrequirements, and the research and devel-opment needed to establish an initial opera-tional coastal ocean prediction system by theyear 2000 (Mooers, 1990a; 1990b). Also,the National Research Council (1989) rec-ommended that the nation establish an “op-erational capability for nowcasting and fore-casting oceanic velocity, temperature, andrelated fields to support coastal (and off-shore) operations and management.” In1993, NOAA developed a strategic plan forestablishing a Coastal Forecast System “tocreate and maintain an effective coastal fore-cast system that meets today’s requirementsand that can be rapidly updated and en-hanced as new requirements, knowledge,and technologies emerge” (U.S. Dept. ofCommerce, 1993). The long-range goal ofsuch a Coastal Forecast System is “to im-prove our ability to measure, understand,and predict coastal environmental phenom-ena that impact public safety and well-be-ing, the national economy, and environmen-tal management.”

As a result, the National Weather Ser-vice (NWS) and the National Ocean Ser-vice (NOS), together with Princeton Uni-versity, have initiated development activitieswithin NOAA for a “Coastal Ocean Fore-cast System” (COFS)—the word “ocean” isspecifically introduced to distinguish it fromatmospheric prediction systems. Now thegeneralized name Regional Ocean ForecastSystem (ROFS) has been adopted to reflectthe fact that (i) such systems can be deployedanywhere in the global ocean, and (ii) thedomain covered by a forecasting system ex-tends far beyond what might strictly be con-sidered a coastal area in several cases in or-der to take into account the influence ofdominant ocean features and processes oc-curring closer to the coast, such as the GulfStream off the U.S. East Coast. The pur-pose of this paper is to describe the needsfor a real-time ROFS, briefly present thehistory of the numerous efforts that have

been undertaken to develop such a capabil-ity, and to describe one system that has nowbecome operational at NCEP for the EastCoast of the U.S. in March, 2002.

2. The Needs for Real-TimeOcean Forecasts

A brief description of the needs for real-time forecasts of ocean conditions, particu-larly in coastal areas, and relevant issues arediscussed in Brink et al. (1992). These is-sues deal with ecosystem management,coastal hazards, navigation, recreation,coastal meteorology, mineral exploitation,defense requirements, fisheries, anthropo-genic inputs, etc. in many of which an op-erational ocean forecasting capability wouldplay an important role.

(a). Marine Transportation and Searchand Rescue Operations: The amount ofcargo transported by ships traversing coastalwaters on their way into ports is expected toincrease substantially in the near future plac-ing greater stress on the coastal environment.Forecast products (ocean currents, water lev-els, and water temperatures) from an oceanforecast system can play a critical role inensuring the safety of, and providing opti-mum routing for, ships at sea. For example,vessels leaving U.S. East Coast ports andheading to Europe can increase their aver-age speed significantly over a major portionof their route by knowing the location ofthe Gulf Stream axis. Knowledge of watertemperature can be important for tankerstransporting crude oil. As water tempera-ture increases, the viscosity of oil decreases,making it easier to pump out the oil whenthe vessel arrives in port. In certain coastalareas, particularly on the East Coast, waterlevel forecasts are critical for safe and eco-nomic operations of marine transportation.

Forecasts of currents and temperature arevital to all hazardous material spill contain-ment efforts and search and rescue (SAR)missions conducted by the Coast Guard inU.S. coastal waters. Surface current infor-mation is required to estimate the directionand extent of spreading of a spill or for thedirection and movement of downed planesand incapacitated vessels prior to search and

rescue operations. Water temperatures areneeded to estimate survival times for thosewho are lost at sea and exposed to hypoth-ermal conditions. For example, following theTWA flight 800 disaster off southern LongIsland on July 17, 1996, information on lo-cal water conditions, particularly near thebottom where the search operations weretaking place, would have been very helpfulduring the search activities which took placein and around the crash site because onlyfour days earlier, Hurricane Bertha hadpassed through this area and stirred up theocean, reducing visibility throughout thewater column.

(b). Coastal Flooding: Storm surges andthe subsequent potential for coastal floodingare ever present dangers in low lying coastalareas. One of the most devastating floodingevents in history that resulted from storm surgeoccurred in Galveston, Texas in 1900. A stormsurge of 20 feet was estimated and as many as12,000 people were killed (Rappaport andFernandez-Partagas, 1995). In 1957, Hurri-cane Audrey produced a storm surge of over12 feet along the Gulf coast which extended25 miles inland in Louisiana, killing almost400 people (Pielke and Pielke, 1997). Accord-ing to Ho et al. (1987), the coastal areas thatare at greatest risk of hurricane encounter liebetween south Florida and Texas. In additionto threatening life and property, coastal flood-ing also causes detrimental changes in beachmorphology and increases erosion. Water lev-els predicted by a ROFS could provide stormsurge forecasts directly if its domain were ex-tended to the coast.

(c). Boundary Conditions for OtherForecast Models: Operational, high-resolu-tion regional ocean forecast models couldprovide initial conditions and boundary con-ditions to support oil spill models, estuarinecirculation models, and coupled ocean-at-mosphere hurricane models (Bender andGinis, 2000). At the present time, lack ofreal-time information on initial conditionsfor the ocean represents a serious limitationin our ability to produce quality forecastsfor both oil spill and coupled hurricane fore-cast models Also, models to predict currents,water levels, salinity, and temperature in anumber of estuaries around the coastal U.S.


are being developed by NOS such as thosefor the Chesapeake Bay (Gross et al., 1999),the Ports of New York and New Jersey (Wei,2003), and Galveston Bay (Schmalz, 2000).Water levels in Chesapeake Bay, for example,are of particular interest to large vessels whichusually have only a small clearance abovethe bottom and thus are susceptible to thedanger of running aground. One of the criti-cal pieces of information that these estua-rine forecast models require is the oceanicforcing where they interface with the coastalocean (i.e., bay mouths).

(d). Offshore Construction and Opera-tions: A knowledge of ocean currents is im-portant for designing offshore structures, forplanning marine construction, and for con-ducting marine operations at sea (Wisemanet al., 1984). During extreme events, cur-rent speeds at the time of peak surface wavesare especially important since their com-bined effect determines the maximum forcesthat are experienced by oil rigs and otherfixed structures deployed offshore. Also, itis important to know current speeds atdeeper levels where drilling and construc-tion activities often take place because cur-rents may still be strong even though theeffects of surface waves will have decreasedsignificantly. Knowledge of current speedsnear the ocean bottom in coastal areas is alsoimportant since vigorous currents in thisregion can lead to sediment erosion,resuspension, and transport. When vigor-ous near-bottom currents exist, resuspensionof bottom sediments can produce major re-ductions in visibility as occurred during theSAR operations following the Flight 800disaster. Vigorous bottom currents, throughthe redistribution of bottom sediments, canalso fill in navigation channels leading to theneed for subsequent dredging operations.

(e). Input to Ecological Forecasts: A pre-dictive modeling capability for U.S. coastalwaters would provide useful information fora number of important ecological problems.The health of our coastal ecosystems is de-clining according to several recent studies(Raloff, 1999). The rise in marine-relateddiseases along the U.S. East Coast, the Gulfof Mexico, and the Caribbean suggests thatconditions conducive to illness are wide-

spread, and that if present trends continue,the health of our ecosystems could be sig-nificantly degraded, resulting in large eco-nomic losses for the fishing industries(Epstein, 1998). Off the East Coast, riverrunoff containing high levels of phospho-rous and nitrogen have been linked to ailingsea grass beds which provide important nurs-eries for a variety of fish. Pollution fromuntreated sewage, industrial wastes, and ag-ricultural runoff during the early 1990’s wasprimarily responsible for the closure of over50% of America’s shellfish beds along theAtlantic and Pacific coasts, and nearly 60%along the coast in the Gulf of Mexico(Hinrichsen, 1998). A survey conducted bythe Natural Resources Defense Council(NRDC, 1996), found that 29 coastal statesand territories had over 3500 beach closingsand pollution advisories in 1995, a 50%increase from 1994, and that most of theclosures were related to high coliform countslinked mainly to partially treated or un-treated sewage, storm runoff, and othermunicipal wastes. The fate of pollutantswhich are being discharged into coastal wa-ters can be predicted based on forecasts froma regional ocean forecast system. Point sourcepollutants, for example, could be routinelytracked and their movements predicted.Such a system could also provide inputs oftemperature, salinity, and water transport toecosystem models which have been, or arepresently being developed. In the bottomwaters which reside on the continental shelfoff Louisiana and Texas, hypoxic conditionsfrequently arise during summer, which re-sult in a so-called “dead zone”. A close rela-tionship exists between the outflow from theMississippi River, river borne nutrients, netproductivity, and bottom water hypoxia inthis region (Rabalais et al., 1994). The physi-cal characteristics and space-time structureof this recurring feature could be trackedthrough the application of a coastal oceanforecast capability. In the New York Bight, acold pool of water forms each year in thespring as the surface waters warm up andisolate the deeper waters below (e.g.,Aikman, 1984). This feature is boundedoffshore by the Slope Water near the conti-nental margin and inshore by warmer wa-

ters in the shallow regions adjacent to thecoast. When fully developed, this water masscan extend from Cape Cod to CapeHatteras. In the fall, increased winds andreduced heating combine to destratify thewater column leading to increased verticalmixing and the subsequent disappearanceof the cold pool. Because of the seasonal iso-lation of the waters that form the cold pool,species of fish which inhabit this region areeffectively trapped until the seasonal break-down of this water mass occurs. As in thecase of the dead zone in the Gulf of Mexico,the capability to forecast the onset, spatialextent, and demise of this unique ocean fea-ture is clearly important.

Over the past 25 years or so, there hasbeen a significant increase in the incidenceof Harmful Algal Blooms (HABs) in U.S.coastal waters. Also, the nature of the HABproblem has changed recently, and largergeographic areas, including most coastalstates, are now threatened by more than oneharmful or toxic species (Boesch et al., 1997).One type of HAB, for example, is caused byhigh concentrations of a toxic algae calledGymnodinium breve (Gb). Gb occurs natu-rally in warm coastal waters, and with a cer-tain combination of temperature, salinity,and nutrients, massive increases in Gb, of-ten referred to as red tides, can occur. Redtides frequently originate in the Gulf ofMexico and are then transported towardshore and along the coast according to theprevailing winds and currents. NOS hasbegun experimental HAB forecasts in theGulf of Mexico based on satellite-derivedocean color data and real-time wind obser-vations (Stumpf et al., 1998). A regionalocean forecast system could predict the tra-jectories and arrival times at specific loca-tions of these harmful algal blooms

(f). Fisheries: For the purpose of fisher-ies management, model-generated fields oftemperature, salinity, and transport will beof great value for applications where it isnecessary to recreate oceanic conditions forpast events that lead to changes in fish be-havior and/or unexplained movements ofspecific fish populations. Forecasts of sur-face and subsurface temperatures could beused by commercial fishermen to make their


operations at sea more efficient by rapidlylocating areas which are potentially fish-pro-ductive. Maps of analyzed sea surface tem-peratures (SST) have been used by fisher-men for many years for this purpose. Bot-tom temperatures are also of interest to thefishermen since they influence the reproduc-tion and recruitment of certain fish whichspend part or all of their life in this environ-ment. Just south of Cape Hatteras, for ex-ample, lies an area called Big Rock wherelocal upwelling contributes to the abundanceof marine life. Several bottom fish includ-ing snapper and grouper are plentiful in theBig Rock area, and, as a result, both com-mercial and recreational fishing take placethere. Marine aquaculture, or mariculture,is another activity that could benefit frominformation provided by a coastal ocean fore-cast system. To successfully culture marinefish and shellfish commercially, informationon the local ambient water conditions is re-quired. If changes in temperature and/orsalinity are too large or too rapid, the fishunder cultivation may be harmed or killed.

(g). Protected Marine Areas: At thepresent time there are 11 National MarineSanctuaries located in U.S. coastal waters.These sanctuaries are managed by NOAAfor protecting a variety of selected marinehabitats. This mission includes restoring andrebuilding marine habitats or ecosystems totheir natural condition as well as monitor-ing and maintaining areas which are pres-ently in good health. In order to accomplishthese goals, information on the existing en-vironmental conditions in these sanctuariesfrom an operational coastal ocean forecastsystem would be beneficial. For example,ecosystem models for diagnosing the healthof the biological communities which inhabitthese sanctuaries will require information ontheir physical state, including temperature,salinity, and currents.

(h). Additional Factors: With respect tothe evolution of ocean forecasting, the devel-opment of Rapid Environmental Assessment(REA), whose purpose is to provide envi-ronmental information in coastal waters ontime scales of use in producing “tactical” fore-casts, is becoming an increasingly impor-tant issue for naval operations (Robinson and

Sellschopp, 2002). Although this develop-ment is primarily related to naval require-ments (Curtin, 1999), it has direct applica-tion to civilian environmental assessment andthus coastal ocean forecasting. A prime ex-ample of the need for rapid environmentalassessment in the civilian sector is the abilityto determine the initial state of the oceanimmediately following an oil spill.

In a cost/benefit analysis involving onlycommercial shipping, recreational boating,and fishing sectors of the marine commu-nity, Kite-Powell et al. (1994) estimated thatthe total expected benefits from an improvedmarine forecasting capability will exceed thecosts of developing and implementing anoperational coastal ROFS by more than anorder of magnitude. When benefits to othermarine users (such as offshore gas and oilindustry, the marine scientific and recre-ational community, and federal, state, andlocal coastal resource managers) are takeninto account, the overall benefits relative tothe estimated costs become even greater.Table 1 summarizes the requirements for aROFS capability and reflects the commentsand suggestions provided by many individu-als and sources.

3. Historical Evolution ofOcean Forecasting

(a). Development of Ocean CirculationModels: Smagorinsky (1963) recognizedthe need to develop ocean circulation mod-els to better understand atmosphere–oceaninteractions on time scales suitable for cli-mate studies. Subsequently, the developmentof ocean circulation models has received agreat deal of attention (see, for example,Sarkisyan, 1962; Bryan and Cox, 1967; andMcWilliams, 1996).

In ocean forecasting, it is necessary todistinguish between short (on the order of afew days), and long-range (on the order ofseasonal to interannual) forecasting. Gen-eral Circulation Models (GCM) for theoceans seem to have been successful to someextent in making long-range forecasts in thetropics because the dominant dynamicalprocesses have much larger temporal andspatial scales than their counterparts at mid-

latitudes and so can be explicitly resolved(Philander, 1990). In short-range forecast-ing, however, the events of interest are fre-quently transient and tend to have time scalesof variability as short as an hour or less. Thismakes them more difficult to forecast thanthe signals associated with long-range fore-casting. Also, as a general rule, the spatialresolution for ocean forecasts needs to bevery fine since the energetic spatial scales ofinterest for the ocean are small compared tothe atmosphere. Coastal areas require evenhigher spatial resolution than the deep openocean because they possess inherently com-plex processes influenced by details ofbathymetry, shore line configuration, freshwater discharges, and open ocean boundaryforcing. In such areas, spatial resolution of akm or less may be needed and makes com-puter resources a critical factor.

The number of regional ocean modelsavailable for predicting the state of the ocean,particularly for coastal areas, has proliferatedin recent years. Haidvogel and Beckmann(1998) evaluated fifteen coastal ocean mod-els. All models are based on the primitiveequations and are fully nonlinear. But themodels differ in some details such as the useof the rigid lid approximation instead of afree surface, different vertical coordinate sys-tems, different numerical approximations,different time stepping schemes, and differ-ent sub-grid-scale closure schemes. Not sur-prisingly, when the results from variousmodels are compared, they often differ. Inparticular, the combined effects of stratifi-cation and steep bottom topography typi-cally encountered in the coastal oceanpresent a particularly difficult problem formost ocean models. Consequently, the prob-lem of model selection is nontrivial andclearly depends on the intended application.

(b). Development of Real-Time ForecastSystems: A limited number of ocean mod-els have been developed for operational usein forecasting the state of the ocean on a realtime basis. During the 1980’s, HarvardUniversity developed an ocean model basedon quasi-geostrophic dynamics called theHarvard Open Ocean Model which wasused to predict the path of the Gulf Stream(Robinson et al., 1996). As a complete fore-


TABLE 1User Requirements for Ocean Forecasts

1 Entire water column ; 2 Entire coastal domain for continental U.S.; 3 Our best estimate4 Unavailable; 5 Platforms/drilling; 6 Primary interest out to 200m depth; 7 Plus retrospective applications.

Activity Forecast Variable Forecast CharacteristicsTemp- Salinity Currents Water Depth Area of Frequency Forecasterature Level Interest Period

Search & Rescue X X EWC1 ECD2 hourly 0-48 hrs7

Oil Spill Models X X X X surface ECD hourly 0-48 hrs

Estuarine Forecast Models X X X X EWC WA3 4/day 0-72 hrs

Ecosystem Models X X X X EWC WA 1/day3 UA4

Mariculture X X X EWC WA 1/day UA

Marine Weather Forecasting X X X surface ECD 4/day 0-72 hrs

Commercial Fishing X X X EWC ECD 4/day 0-72 hrs

Commercial Shipping X X X X EWC ECD 4/day 0-72 hrs

Recreational Boating X X surface ECD 2/day 0-48 hrs

Salvage & Mining X X X EWC ECD 4/day 0-72 hrs

Oil & Gas5 X X X EWC WA 4/day 0-72 hrs

Fisheries Mgmt. & Research X X X EWC ECD Variable Retrospective

Ship Routing X X X surface ECD 4/day 0-72 hrs

Military Applications X X X X EWC Littoral Zone 4/day 0-72 hrs

Coastal Zone Management X X X X EWC ECD 1/day UA

Marine Science Community X X X X EWC WA Variable Variable

casting system, the model included an ob-servational data network and statistical mod-els which, together, provided the necessaryinitial conditions to run the model opera-tionally. This model was primarily intendedto forecast the evolution of the Gulf Streamand its associated eddies, and not the circu-lation over the shelf. Consequently explicitsurface forcing from an atmospheric modelwas not required. The system producedweekly, seven-day forecasts between 1986and 1989. A different forecast system, theGreat Lakes Forecasting System (GLFS), hasbeen developed by the Ohio State Univer-sity and the Great Lakes EnvironmentalResearch Lab/NOAA (Schwab and Bedford,1994) to provide nowcasts and short rangeforecasts of the physical conditions of someof the Great Lakes. The primary componentsof the GLFS are the Princeton Ocean Model(POM) (Blumberg and Mellor, 1987) anda wave model (Bedford and Schwab, 1994).Because each of the Great Lakes is essen-tially a closed system with no open bound-aries, the problem of prescribing lateralboundary conditions does not arise. This

system is currently in the process of becom-ing fully operational at NOAA with NCEPtaking responsibility for wave forecasting,and NOS for the circulation component.

A POM-based operational forecast sys-tem, forced by the Canadian Meteorologi-cal Center’s atmospheric forecast model, isbeing developed to forecast the state of thewaters off the east coast of Canada(Bobanovic and Thompson, 1999). Bound-ary conditions for the model’s open bound-aries are obtained from a large-scale stormsurge model. The model domain includesthe Gulf of Saint Lawrence and the Scotianshelf and has a horizontal resolution of 1/16°x 1/16°in latitude and longitude. The U.K. Meteorological Office (UKMO) hasimplemented a global ocean circulationmodel called the Forecasting Ocean-Atmo-sphere Model (FOAM). The model is basedon the primitive equations and has 20 lay-ers in the vertical. It is forced by the UKMO’soperational atmospheric forecast model (Bellet al., 2001). Since the horizontal resolutionis 1° x 1°, only the general features of thecirculation can be represented in coastal ar-

eas. A coastal ocean forecast system calledSOPRANE (Système Océanique dePrévision Régionale en Atlantique Nord Est)is used by the French (Giraud et al., 1997)as part of their ongoing SOAP (SystèmeOpérationel d’Analyse et de Prévision) pro-gram. The system is based on a 1/10° quasi-geostrophic model of the Northeast Atlan-tic from 24°N–54°N, 35°W to the coast,and terminating at the 200m isobath (butnot including the Mediterranean Sea). Thesystem runs every week providing a 2-weekforecast of the ocean circulation and ther-mal structure. A coastal ocean forecast sys-tem is also being developed by the Norwe-gians for the North Atlantic and Nordic Seaswith enhanced resolution in the Europeancoastal zones (e.g., Guddal, 1999). The pri-mary purpose of this effort is to develop anadvanced data assimilation system to be usedwith a coupled primitive equation ocean cir-culation model together with a marine eco-system model for the regions indicated.More recently, the European community hasdeveloped a COupled HydrodynamicalEcological model for REgioNal Shelf seas


(COHERENS). This model is fully three-dimensional and is intended for use in coastaland shelf seas. A full description can be ob-tained at: http://www.mumm.ac.be/~patrick/mast/. Although this state-of-the-art coastal circulation model is presentlybeing used primarily for research, it is likelythat it will find operational use in the nearfuture. Finally, the U.S. Navy is extensivelyinvolved in ocean forecast model develop-ment, implementation, and data assimila-tion. Recent summaries of this work can befound in Oceanography (2002).

4. Description of East Coast- Regional Ocean ForecastSystem (EC-ROFS)

An earlier version of ROFS, whichstarted as a joint effort between NOAA’sNWS, NOS, and the Princeton Universitywas called the Coastal Ocean Forecast Sys-tem (COFS), and was described in Aikmanet al. (1996). However, many changes tothe system have taken place since then, in-cluding its name (now EC-ROFS).

(a) Selection of Forecast Domain: Anarea off the East Coast of the U.S. was cho-sen as the pilot domain to test the feasibilityof producing real-time coastal ocean fore-casts. The model domain extends from ap-proximately 26.5° to 48°N, and from theU.S. East Coast out to 50°W (Fig. 1). Thechoice of the U.S. East Coast was made be-cause the Gulf Stream (GS), which covers amajor portion of the domain, provides arobust signal and may be somewhat betterunderstood compared to the CaliforniaCurrent System off the West Coast. Also,the quality of the atmospheric forcing is bet-ter determined off the East Coast becauseof the large number of upstream (i.e., conti-nental) meteorological observations that areavailable for assimilation into the atmo-spheric forecast model. The model domaincovers approximately 4.27x106 km2 and con-tains one landward boundary and two openboundaries, one along its southern and theother along its eastern extremities. It wasrecognized from the outset that the task ofspecifying the open boundary conditionsalong its southern and eastern boundaries

would be problematic. The model domainencompasses a number of major ocean fea-tures such as different water masses, currents,frontal zones, and river plumes. Some of thefeatures are permanent, but transient featuressuch as eddies associated with the GS alsooccur in the region. The circulation off theEast Coast domain is also significantly in-fluenced by outflows from the major riversand bays. The five largest outflows of lowsalinity water along the east coast are pro-duced by the St. Lawrence River, Connecti-cut River, New York Harbor, Delaware Bay,and the Chesapeake Bay. Low salinity wa-ters are discharged from each of these sourcesproducing plumes which may extend 50kmor more offshore. In the case of the St.Lawrence River the outflow extends acrossa region which is approximately 100 kmwide. For the Connecticut River, the out-flow is discharged initially into Long IslandSound where it spreads to the east past thetip of eastern Long Island and onto the con-tinental shelf. These plumes of low salinitywater add buoyancy to the shelf waters andare affected by the earth’s rotation. Dischargefrom rivers further south along the east coastsuch as the Santee River in South Carolinaand the Savannah River in Georgia also pro-

duce plumes but are smaller in scale and soare not well-resolved in the model at thepresent time.

(b) The Model: The Princeton OceanModel (POM) is used to generate forecastsproduced by EC-ROFS. The POM is athree-dimensional ocean circulation modelbased on the primitive equations and em-ploys a free surface. It uses a terrain-follow-ing sigma coordinate in the vertical, and acoastal-following curvilinear grid in the hori-zontal. The model has 19 levels in the verti-cal with higher resolution in the mixed layerand the upper thermocline. The spatial reso-lution increases from 20 km offshore to10km near the coast. The coastal boundarycorresponds to the 10 m isobath. The modelbathymetry is based on the U.S. Navy’s Digi-tal Bathymetric Data Base with 5-minuteresolution (DBDB-5). Improvements to theDBDB-5 bathymetry have been incorpo-rated over the continental shelf and slopeusing recently acquired bathymetric datafrom NOS at 15-second resolution (Wei,1995). The momentum equations are fullynonlinear with a variable Coriolis param-eter and a second order turbulent closuresubmodel to parameterize vertical mixing.Horizontal diffusion is based on the pa-

FIGURE 1EC-ROFS domain including the horizontal grid, the major bathymetry, inflow and outflow boundary conditionsalong the open boundaries, and the rivers that currently discharge fresh water into the model domain.


rameterization of Smagorinsky (1963). Theprognostic variables are temperature, salin-ity, and the horizontal components of ve-locity, and the free surface. For a completedescription of the POM and its numericalschemes, see Blumberg and Mellor (1987).

(c) Surface Forcing and Lateral Bound-ary Conditions: NCEP’s operational Etamodel (see http://www.nco.ncep.noaa.gov)provides the surface fluxes of heat, moisture,and momentum every three hours. The fore-cast parameters from the Eta model are avail-able at a height of 10 m above the surface.The specific parameters which are extractedare the sensible and latent heat fluxes, the netshortwave and downward longwave radiationfluxes, friction and wind velocities, and theprecipitation minus evaporation. The currentversion of EC-ROFS includes astronomicaltidal forcing along the open boundaries andbody forcing within the model domain forsix tidal constituents: three semi-diurnal com-ponents (M

2, S

2, and N

2) and three diurnal

components (K1, O

1, and P

1). A least squares

optimization technique was developed todetermine the tidal forcing on the openboundaries using tidal constants within themodel domain (Chen and Mellor, 1999).

The model is driven along its openboundaries using climatological estimates oftemperature and salinity from the Navy’sGlobal Digital Environmental Model(GDEM), and volume transport which isspecified separately. Along the southernboundary (Fig. 1), inflows totaling 58.25Sverdrups (Svs) and an outflow of 36.25Svs are prescribed and are distributed hori-zontally in accordance with measurementsmade during the SubTropical Atlantic Cli-mate Studies (STACS) program (Leamanet al., 1987). Along the eastern boundary at50°W, 90 Svs exit the domain between 37°and 40°N reflecting the expected transportassociated with the Gulf Stream at that lo-cation. Inflow north of the GS representsthe estimated transport associated with theLabrador Current Extension (38 Svs), andinflow to the south represents inflow associ-ated with the subtropical recirculation gyre(30 Svs). Temperature along the openboundaries is based on the monthly GDEMclimatology whereas salinity is based on the

annual GDEM climatology. For additionaldetails concerning the specification of theopen boundary conditions, see Kelley et al.(1999). Fresh water inputs are specified for16 rivers, bays and estuaries along the U.S.East Coast and are based on a stream flowclimatology by Blumberg and Grehl (1987).The locations of rivers and bays that dis-charge fresh water into the model domainare shown in Fig. 1, and monthly mean val-ues from this climatology are used to pre-scribe the fresh water that is discharged.

(d) Operations: In order to start a fore-cast each day, a hindcast cycle is used to pro-duce new initial conditions for that day us-ing the following procedures. Sea surfaceheight anomalies (SSHA) from satellite al-timeters are first assimilated into the initialconditions from the previous day. Then start-ing with these modified model fields, thePOM is integrated forward to the currenttime using analyzed fluxes during the last 24hours provided by the Eta Data AssimilationSystem (EDAS) while also assimilating SSTdata obtained during the last 48 hours. (Meth-ods used to assimilate SSHAs and SST’s willbe described later.) This completes thehindcast cycle and provides new initial con-ditions for starting the forecast cycle each day.

Since January 1997, the output fieldsfrom the model including both oceanicnowcasts and forecasts as well as the atmo-spheric flux fields from the Eta model wereautomatically transferred to NationalOceanographic Data Center (NODC) forrapid online access to outside users. The re-sults are available online at NODC for upto three months and then are transferred topermanent storage media for archiving. Themodel output fields are also available fromthe archives upon request (contact http://polar.ncep.noaa.gov for information).

(e) Sample Forecast Products: The basicforecast fields from EC-ROFS that are pro-duced and examined routinely are nowcastsand 24-hour forecasts of SST, temperatureat 200 meters, bottom temperature over thecontinental shelf, sea surface salinity, salin-ity at 200 meters, surface currents, currentsat 200 meters, and finally, surface elevation.Here we present several examples of theseforecast products.

In Fig. 2, an SST forecast valid at0000UTC on August 26, 2003 is shown inthe upper left-hand corner. Cooler waters overthe continental shelf and warmer waters inthe Gulf Stream and Sargasso Sea are evident.In the lower left-hand corner of the figure, a

FIGURE 2Sample forecast products from EC-ROFS: SST (upper left), sea surface salinity (lower left), bottom temperatureover the continental shelf (upper right), and surface elevation (lower right).


forecast of surface salinity valid at 00 UTCon August 26, 2003 is shown. The influenceof fresher waters from the Gulf of St.Lawrence, and in the Gulf of Maine can beseen. Although river discharge plumes of lowsalinity water are often produced in the model(Chesapeake Bay, for example), these plumes,when they can be detected, are not expectedto be realistic since monthly climatologicalstreamflows are presently employed in themodel. Work is currently underway to replacethe climatological streamflows with daily ob-served streamflows from the U.S. GeologicalSurvey (USGS). Bottom temperatures fromthe lowest level in the model for August 26,2003 are shown in the upper right-hand cor-ner of the figure. Because the vertical coordi-nate system in EC-ROFS is terrain-follow-ing (i.e., sigma coordinate), no conversion isneeded to display any of the output fields inthe bottom layer of the model. Bottom tem-peratures are of interest to fishermen andmarine biologists because many species of fishreproduce and live at least part of their exist-ence on, or near, the ocean bottom. Bottomtemperatures do not change rapidly on theshelf but changes of several degrees can occurover periods of several months. In this figure,model-predicted bottom temperatures arealmost 10°C higher over the shelf south ofCape Hatteras than they are north of CapeHatteras. Not surprisingly, model-predictedbottom temperatures are very difficult toverify since most in situ temperature observa-tions do not reach the bottom. In the lowerright-hand corner of Fig. 2, a 24-hour fore-cast of surface elevation over the model do-main is shown for August 26, 2003. A largeincrease in surface elevation occurs across theNorth Wall of the Gulf Stream. The surfacerises by as much as 70 cm proceeding fromthe Slope Water, across the Gulf Stream, andinto the Sargasso Sea. Higher elevations arealso seen in the Gulf of Maine.

5. Evaluation of EC-ROFSForecast Fields

This section deals with a number of com-parisons between model generated forecastsand observations. The comparisons are lim-ited to temperature and water levels since

FIGURE 3Seven-day changes in SST from EC-ROFS (dashed), compared with seven-day changes in SST from buoy44028 (solid) located in shallow water just off of Buzzard’s Bay, Massachusetts for October through December1995, prior to data assimilation (top). Comparison of nowcast SSTs from EC-ROFS (dotted) with observedSSTs from buoy 44138 off the Grand Banks for a 150-day period from June to December 1997(after SST dataassimilation was implemented - bottom). (COFS3.2n was an earlier version of EC-ROFS)


observations of currents and salinity are gen-erally not available. For temperatures, mostcomparisons are made before and after in-troducing data assimilation into the model.Comparisons of water levels at the coast aremade before and after tidal forcing was in-troduced into the model.

(a) Assimilation of Sea Surface Tempera-ture (SST) Data: Prior to the assimilation ofSST data in EC-ROFS, large differencesexisted between model generated forecastsor nowcasts and observations. As an exampleof the SST variability without data assimila-tion, Fig. 3 (top panel) shows a comparisonof SST differences between buoy observa-tions and model predictions. In this panel,7-day changes, stepping through the recordone day at a time, are compared at a nearcoastal location off Buzzard’s Bay, Massachu-setts. The comparison covered a period of80 days from October–December, 1995.Even though the general pattern of changeis remarkably similar, the variability is clearlymuch greater in the observed changes thanit is in the predicted changes.

In order to minimize the temperaturedifferences between the model and the ob-servations, assimilation of SST data, fromin situ and satellite observations receivedduring the most recent 48 hours, has beenimplemented in EC-ROFS. The in situ ob-servations are obtained from U.S. and Ca-nadian fixed buoys, drifting buoys, Coastal-Marine Automated Network (C-MAN) sta-tions, and ships participating in the Volun-tary Observing Ship (VOS) program.Within the model domain there are 27 fixedbuoys and C-MAN stations and 5-10 drift-ing buoys which report SST on any givenday. The remotely-sensed observations con-sist of multi-channel SST (MCSST) retriev-als derived from the Advanced Very HighResolution Radiometer (AVHRR) on boardNOAA’s operational polar-orbiting satellites.Each retrieval represents approximately an8 x 8 km area. The number of retrievals inthe domain on a given day, depending oncloud cover, ranges from 400 to 7000.

The data assimilation scheme is based onthree steps. In the first step, an SST correctionfield is obtained using an equivalent variationalformulation. In the second step, the surface

FIGURE 4Comparison of EC-ROFS 24-hour forecasts of SST before (dotted) and after (dot-dash) SST data assimilationwas implemented, with observed SSTs from buoy 44008 off Nantucket Island for a 12-day period in March1997 (top). Comparison of EC-ROFS 24-hour forecasts of SST before (dotted) and after (dot-dash) SST dataassimilation was implemented, with observed SSTs from the C-MAN station off the mouth of Chesapeake Bay(36.9°N, 75.7°W) for the same 12-day period in March 1997 (bottom). (COFS3.1 and 3.2 were earlier versionsof EC-ROFS. COFS3.1 was without data assimilation, and COFS3.2 was with data assimilation)


correction field is projected downward into themixed layer following the method of Chalikovand Peters (1997) to create a 3-D correctionfield for temperature. Finally, a nudging pro-cedure is used to slowly apply the 3-D correc-tion field through the model’s mixed-layer. SeeKelley et al. (2002) for details.

Fig. 3 (bottom panel) compares buoy-observed SSTs with model produced SSTsat a buoy located near the Grand Banks af-ter data assimilation was introduced. Theperiod covers approximately 150 days be-tween June–December, 1997. Although thepatterns of change in SST are similar, thereare systematic differences between the ob-served and predicted values throughout therecord that might be missed if only the meandifference was considered.

Fig. 4 shows comparisons of SST be-tween two National Data Buoy Center(NDBC) buoys and the model, the first offNantucket Island (top panel), and the sec-ond, off of the mouth of the ChesapeakeBay (bottom panel). In both cases, the same12-day period during March 1997 was em-ployed. At the location off Nantucket Island,the impact of data assimilation is to improvethe agreement between the model and theobservations by 2-3°C. Off the mouth ofthe Chesapeake Bay, the improvement iseven more striking. In this case the improve-ment is closer to 5°C. At most buoysthroughout the model domain improve-ments of ~1°C or more were observed.

Next we compare vertical profiles of tem-perature from the model with observed pro-files acquired using eXpendableBathyThermographs (XBTs) (Fig. 5, top andbottom panels). The profiles shown in thetop panel are located just beyond the conti-nental shelf at approximately 38°N, 73°Wand were acquired on March 1, 1997. Eventhough marked improvement is shown inthe profile with data assimilation when com-pared to the XBT profile, the vertical struc-ture of the “improved” profile still does notagree well with the in situ data. The profileshape and the depth of the mixed layer areclearly not in close agreement with the ob-served temperature profile. In the bottompanel of Fig.5, temperature profiles in deepwater (> 4000m) south of Nova Scotia for

FIGURE 5Vertical profiles of temperature from XBTs (solid line) compared with profiles from EC-ROFS before (shorterdashes), and after (longer dashes) SST data assimilation was implemented, for a location just beyond the shelfbreak at approximately 38°N, 73 °W, for March 1, 1997 (top). Vertical profiles of temperature from XBTs (solidline) compared with profiles from EC-ROFS before (shorter dashes), and after (longer dashes) SST data assimi-lation was implemented, for a deep water location at approximately 41°N, 63.5°W, for March 4, 1997 (bottom).(COFS3.1 and 3.2 were earlier versions of EC-ROFS. COFS3.1 was without data assimilation, and COFS3.2 waswith data assimilation)


March 4, 1997 are compared. Again, muchbetter agreement with the observed profileis seen for the case where data assimilationhas been included even though the lack ofagreement at deeper levels still persists. Someof the disagreement may be attributed tofactors such as parameterization of mixingand lateral boundary conditions.

(b) Assimilation of Sea Surface HeightAnomalies (SSHA): SSHA’s obtained fromthe altimeter aboard the TOPEX/POSEIDON satellite are assimilated into theocean model using a method developed byEzer and Mellor (1997). The SSHA’s arecalculated from a three-year mean surfaceelevation field. Optimal interpolation is usedto interpolate the SSHA’s along the satellitetracks horizontally onto the EC-ROFS grid.The assimilation technique assumes that theSSHA and subsurface temperature and sa-linity are related. Using the POM as a basis,correlations between SSHA’s and the verti-cal structures of temperature and salinity arecalculated for each grid point in the modeldomain where bottom depth > 2000 m.These correlations are seasonally dependentand this dependence has been taken intoaccount in establishing the SSHA/subsur-face temperature and salinity relationships.These correlations are used as the basis forassimilating the TOPEX altimeter data intoEC-ROFS. Because the technique only ad-dresses the baroclinic structure, it can notbe used in shallow shelf areas wherebarotropic contributions to sea surface el-evation play an important role.

A control run without altimeter data(Fig. 6a), and a parallel run with altimeterdata (Fig. 6b) were made for a period fromMay through July 1999. The most recent10 days of SSHA data from TOPEX are as-similated into the model. Fig.6b shows ananticyclonic eddy near the GS at approxi-mately 39.5°N, 65°W in the surface veloc-ity field in the parallel run (with TOPEXassimilation) that does not appear in the con-trol run shown in Fig. 6a (without TOPEXassimilation). The existence of this featurewas verified with imagery from the GOES-8 satellite acquired at the same time whichshowed a GS meander about to pinch off atthis location (not shown - see CMDP, 2001).

FIGURE 6(a) A nowcast of surface currents from EC-ROFS for June 3, 1999 without the assimilation of TOPEX altimeterdata or Gulf Stream path data (Version II), during the CMDP (see text for details). (b) A nowcast of surfacecurrents from EC-ROFS for June 3, 1999 with the assimilation of TOPEX altimeter data and Gulf Stream pathdata (Version III), during the CMDP. In the second case, (i.e., with data assimilation), a Gulf Stream eddyappears at 39°N, 65°W, whose existence was verified independently with imagery from the GOES-8 satellite.


Because the assimilation scheme is based onthe correlation between SSHA and subsur-face temperature and salinity, it was antici-pated that improvements might be obtainedin the subsurface temperature structure.

Fig. 7 shows a comparison of an observedtemperature profile (solid line) with profilesfrom EC-ROFS, with only SST data assimi-lation (dotted line), and with both SST andSSHA data assimilation (dashed line) forMay 17, 1999 at 37.3°N, 52.1°W. Someimprovement in the agreement between theobserved profile and the model-generatedprofile that includes SSHA assimilation isapparent. However, such improvement inthe vertical temperature (and salinity) struc-ture was not true in all cases. Part of the rea-son for this could be related to the fact thatassimilation of SSHA data depends on us-ing model-generated vertical correlationsbetween the surface elevation anomaly andtemperature (and salinity) and such correla-tions not only can not be expected to be ac-curate due to the inherent deficiencies of anygiven model but can also contribute to de-teriorating the intrinsic value of an other-wise valid observation.

(c) Water Levels: EC-ROFS has shownconsiderable skill in predicting water levelsat the coast with, and without, tidal forcing(e.g., Aikman et al., 1998). The highest skillhas been achieved for the subtidal water lev-els which are strongly influenced by the windforcing provided by the Eta model. In thissection, we present an evaluation of thecoastal water level forecasts produced by themodel with wind forcing only and with bothwind and tidal forcing using the pre-spring2001 version of the model that used the pre-vious day’s 24-hour forecast as the initial con-dition for the next day’s forecast. We alsoshow a forecast using the present 24-hourhindcast cycle, as discussed in section (4d),to generate initial conditions. Data fromNOS’s National Water Level ObservationNetwork (NWLON) gages along the NorthAmerican East Coast are used to evaluate thecoastal water level forecasts. Fig.8 shows acomparison of water level observations withforecasts of subtidal water levels at Eastport,Maine, and Atlantic City, New Jersey, usinginitial conditions from a hindcast simulation

FIGURE 7Comparison of an observed XBT profile with EC-ROFS using only SST assimilation (dotted line), and then usingSST plus SSHA assimilation (dashed line). The location is 37.3°N, 52.1°W for May 17, 1999. (CFS3.2 includesonly SST data assimilation, whereas CFS3.4 includes both SST and SSHA data assimilation. Both are predeces-sors of EC-ROFS)

FIGURE 8Model and observed subtidal (30-hour low-pass filtered) water level time series at two stations (Eastport, MEand Atlantic City, NJ) for July and August, 1996. The solid line is the observed data, the dashed line was for thecurrent version of EC-ROFS at this time (i.e., Version 3.0), and the large, dotted line is the nowcast/forecastsimulation.


versus the conditions from the previous day’s24-hour forecast for the period from Junethrough August 1996. These results indicatethat the 24-hour hindcast cycle presentlybeing used further improves the model’ssubtidal response by about 20%. Wind gen-erated responses are well represented in theforecasts even though there are some occa-sional disagreements in phase and amplitude.

Tidal forcing was introduced into theforecast system in May 1996. Both astro-nomical tidal forcing along the open bound-aries and astronomical body forcing withinthe model domain are included. A least-squares optimization technique was devisedto solve for the boundary tidal forcing (Chenand Mellor, 1999), wherein the boundaryforcing is represented by a series of modeswhich are coupled to the model through aresponse function that is determined by run-ning the model. The optimal boundary forc-ing coefficients are obtained by minimizingthe error between the model and observa-tions at tidal stations within the domain.Twelve months of experimental results in-dicate that the tides improve the modelsubtidal response at the coast, reducing RMSerrors by more than 10%.

(d) Evaluation of Results from theCoastal Marine Demonstration Project: TheCMDP was a two-year program, initiatedin 1998, whose purpose was to demonstratethe state-of-the-art in coastal marine fore-casting. The program was sponsored by theNational Ocean Partnership Program. As apartnership, eight organizations, includingthe federal government, academia, and theprivate sector, worked together to plan, pre-pare for, and conduct the CMDP. The studyarea for this project included the Chesa-peake Bay and the surrounding coastalocean (32°- 42°N, and from the coast outto 70°W) and falls completely within theEC-ROFS domain. The demonstrationconsisted of two phases. The first phase tookplace during June-July of 1999 and the sec-ond during February-April, 2000. A broadcross-section of the marine community wasselected to evaluate the various nowcast/forecast products that were generated anddistributed in real-time during these dem-onstration periods. Forecasters from

NCEP’s Marine Prediction Center (MPC,which is now called the Ocean PredictionCenter), and NOAA’s Coastal Services Cen-ter (CSC) in Charleston, South Carolinahad the responsibility of evaluating specificproducts from EC-ROFS for the CMDP.During the first phase of the CMDP, thefollowing EC-ROFS-related products wereprovided: SST, surface salinity, and surfacecurrents. During the second phase, twoadditional EC-ROFS forecast products wereincluded: temperature at 50m, and bot-tom temperature. Only a summary of theCMDP results are given below (see Szilagyiet al., 2000 for details).

The MPC evaluated all of the productsthat were generated from the ocean modelfor the CMDP and noted several deficien-cies. EC-ROFS had difficulty in predict-ing the correct location of the GS and itsassociated eddies. In particular, unrealisticbehavior was observed just beyond CapeHatteras where an anomalous meander of-ten developed. Also, SST gradients justnorth of the Gulf Stream were too weak,compared to independent analyses andobservations. Surface currents, particularlyover the continental shelf, often did notreflect the prevailing background flowwhich was to the southwest. Evaluationsby the CSC were based on comparisonswith AVHRR imagery received on site. Themost significant problems were the inabil-ity of EC-ROFS to reproduce the high ther-mal gradients associated with the NorthWall of the GS, and the anomalous behav-ior of the GS just beyond Cape Hatteras,in agreement with the findings of MPC.On the positive side, CSC indicated thatalthough significant problems in locatingthe position of the GS did exist, these defi-ciencies were generally systematic so thatforecasters could make allowances for themin their forecasts in a manner similar to theway they normally handle known deficien-cies in numerical weather prediction mod-els. Due to the lack of data, salinity fieldswere not quantitatively evaluated, but it wasnoted that the freshwater plumes emanat-ing from major bays and estuaries alongthe east coast appeared to respond to windforcing in a realistic manner.

6. Problems: Past and PresentAs indicated in section 1, the develop-

ment of a system to forecast the state of thecoastal ocean is one of the most difficult tasksthat faces the modeling community. Con-sequently it should come as no surprise thatnumerous problems have arisen during thecourse of developing EC-ROFS. Some ofthe problems are clearly related to the pre-scription of outer boundary conditions,some are related to the lack of sufficientocean data and optimal data assimilationtechniques to improve the initial conditionsin the model, and others are related to defi-ciencies in model resolution, numerics,parameterizations, physics, and the imposedexternal atmospheric forcing. As discussedin this section, some of these problems havebeen resolved and some still remain to beresolved (see Breaker and Rao, 1998, foradditional details).

(a) Anomalous Increase in SST: In theearly stages of evaluating COFS, the prede-cessor to EC-ROFS, a large positive bias inSST developed over the model domain withtemperatures at least 5°C higher than ob-served values. This problem was traced tothe significantly higher values of net surfaceheat flux from the Eta model compared tosurface heat fluxes from the ComprehensiveOcean Atmosphere Data Set (COADS) cli-matology (Woodruff et al. 1987). The la-tent and sensible heat fluxes, and the incom-ing short wave radiation in the Eta modelwere much higher than those normally ex-pected over a wide range of atmosphericconditions. As a result of these findings, sev-eral refinements have been made to the heatflux parameterizations in the Eta model toreduce the net heat flux (Black et al., 1997).For the incoming short wave radiation, sev-eral new features were added including theintroduction of atmospheric absorption byozone and aerosols, and the replacement ofa circular orbit for the earth by an ellipticalorbit. The inclusion of these factors reducedthe incoming short wave radiation by ap-proximately 10%. Certain other adjustmentswere also introduced into the model to keepthe magnitude of the net surface heat fluxesconsistent with the expected climatologicalvalues. Such uncertainties in the fluxes pro-


vided by an atmospheric forecast model haveemphasized the need to carefully evaluatethe surface fluxes derived from NWP mod-els before using them in an ocean model.This experience has clearly demonstratedthat ocean models can highlight deficien-cies in certain parameterizations in atmo-spheric models that might have otherwisegone undetected.

(b) Specification of Lateral BoundaryConditions: The model domain for EC-ROFS has large open boundaries along itssouthern and eastern extremities. Adoptionof a limited-area model was dictated by theneed for relatively high spatial resolution in-side the model domain and computationalconstraints imposed by available resources.However, adequate specification of the re-quired open boundary conditions (OBCs)along these boundaries has been, and con-tinues to be, a serious problem (e.g.,Westerink and Gray, 1991). Numerous meth-ods have been used to address this problemwith varying degrees of success. See Johnsen(1994) for an overview of these methods.

At the present time, climatological val-ues of temperature (monthly), salinity (an-nual), and volume transport are used tospecify the OBCs in the model domain. Fortemperature and salinity, the GDEM clima-tology has been employed. Estimates of thevolume transport into and out of the modeldomain have been obtained from varioussources (see, for example, Hogg, 1992). Un-fortunately, climatological values of tempera-ture, salinity, and transport are not represen-tative of the actual conditions and do notcontain the important mesoscale structureand high frequency variability characteristicof real-time ocean processes. As mentionedearlier, the model domain was chosen to belarge to prevent boundary generated errorsfrom propagating into the areas of interest—namely, the coastal region. However, in anoperational environment, the model runsevery day and errors from unrealistic OBCswill eventually propagate into the coastalregion and effect the quality of the results inspite of attempts to nudge the model towardsreality through data assimilation.

One of the problems evident in the fore-cast fields produced by the model is the con-

sistent lack of flow to the southwest over theshelf and inner slope region that lies betweenthe Gulf Stream and the coast. This defi-ciency is almost certainly related to theboundary conditions prescribed along theeastern extremity as well as the fresh waterinflows on the landward boundary of themodel domain. Historic Eulerian currentmeter data and Lagrangian trajectories fromdrifters in this region consistently indicateflow to the SW at speeds of up to 10 cm/sec. Sensitivity studies were conducted todetermine if persistent flow to the SW couldbe produced by modifying inflow conditionsalong the eastern boundary north of the GulfStream. As transport across the boundarywas increased, most of the additional inflowwhich initially entered the domain, turnedto the south and then to the east, finally ex-iting the domain just south of the regionwhere it had been injected, i.e., just north ofthe Gulf Stream. This experiment showedthat intuition does not always lead to thedesired results!

An alternate approach to specifying theOBCs is to embed or nest the regional modelwithin a basin scale model. Oneway ortwoway coupling between the models alongtheir common boundaries will provide theregional model with the required real-timeinformation on lateral forcing. As discussedin Warner et al. (1997), however, modelnesting also has a number of limitations gen-erally related to mis-specification of the lat-eral boundary conditions. They includechanges in spatial resolution at the bound-ary between the models, poor initial infor-mation from the global model, differencesin the process parameterizations between themodels that can lead to spurious propertygradients at the boundary interface, and, fi-nally, the generation of transient distur-bances at the interface that may interact withthe desired solution on the interior of theregional model domain. However, follow-ing the example of model nesting in numeri-cal weather prediction, efficient nesting tech-niques need to be introduced to develop lim-ited area circulation models for the coastalocean. Such an effort is currently underwayat NCEP using the Hybrid CoordinateOcean Model (HYCOM) system as the ba-

sis (see Bleck, 2002 for details on theHYCOM system).

(c) Freshwater Influxes and Coastal Sa-linities: Along the landward boundary of theEC-ROFS, 16 bays, rivers, and estuaries dis-charge fresh water into the model domainthat have a major impact on the distribu-tion of salinity near the coast. As a result, inmany coastal areas, the circulation may beprimarily governed by salinity and not bytemperature. This was clearly shown to bethe case for the low salinity plume off theChesapeake Bay (Breaker et al., 1999), forexample. Improved freshwater fluxes alongthe coastal boundary of the model domainare essential to describe salinities and theprimary circulation characteristics near thecoast in a more realistic manner.

At this time, the specification of fresh-water discharge for 16 coastal entry pointsis based on the monthly climatology ofBlumberg and Grehl (1987) which does notcontain information on major episodicevents such as tropical storms and hurricanes,or periods of drought, deficiencies that maylead to significant departures from the cli-matology. In order to improve this situation,efforts are underway to replace the monthlyclimatological outflows used presently in themodel with observed daily values from theUSGS’s network of gages that measurestreamflows for all of the major rivers in theU.S. In some cases, readings from one gagemay be representative of the actual outflowinto the model domain. However, in caseslike the Chesapeake Bay, estimating the to-tal outflow at the mouth of the bay is prob-lematic since at least nine rivers dischargewaters into the bay, and the time requiredfor these waters to circulate through the bayis difficult to estimate. In some cases,groundwater contributes to the outflow, fur-ther complicating the problem.

(d) Ocean Data Assimilation: An accu-rate specification of the initial conditions isa necessary pre-requisite to produce reliableforecasts from any model. This is accom-plished through the incorporation of ad-vanced data assimilation techniques into thenowcast/forecast system. At the present time,SST’s from satellite retrievals and from insitu reports are being assimilated and their


influence is projected down through themixed layer. The vast majority of SST datacomes from satellites and so their availabil-ity depends on cloud cover. In the GS re-gion, a primary area of interest, cloud coveris a persistent problem. The time scales ofvariability for the Gulf Stream are as shortas 2 - 3 days, and frequently, several days ormore elapse before new coverage can be ob-tained in this region. Hence, the fact thatthe distribution and density of available sat-ellite-derived SSTs is cloud cover-dependentpresents a major problem for ocean data as-similation. It is also important to assimilatedata at deeper levels, particularly in the areaof the GS in order to reproduce realistic sur-face (and subsurface) flow fields. The onlysources of available subsurface data are fromXBT’s and ARGO type floats. But, unfor-tunately, data from these sources are sparse.Often less than 10 XBT’s are available withinour model domain on any given day andtheir distributions are usually unfavorable forresolving the features of interest. Neverthe-less, methods are being tested to assimilatedata from XBT’s and ARGO and PALACEfloats. In assimilating XBT data, makingcorrections to subsurface temperature aloneis not necessarily sufficient to bring themodel fields closer to reality. It is also neces-sary to make corresponding adjustments tothe associated salinity field to prevent po-tential gravitational instabilities (Chalikov etal., 1998).

Surface elevation anomalies from altimeterdata, as discussed earlier, are being assimi-lated to correct the subsurface temperatureand salinity structure. There are problems,however, with the existing data, and the as-similation scheme for application to high-resolution, real-time regional ocean forecastmodels, particularly in coastal areas. For theTOPEX/POSEIDON satellite, for example,adjacent track lines are approximately 250km apart with a repeat cycle of 10 days. Witha track spacing this coarse, many mesoscaleocean features are missed, and with a repeatcycle of 10 days, it is difficult to considerthese data suitable for real-time forecast ap-plications. Perhaps even more serious prob-lems relate to how the data are being assimi-lated. In particular, using vertical correlations

generated from an imperfect model to projectthe SSHA into the model interior to correctthe baroclinic part of the model dynamics islikely to produce undesirable effects. It is nec-essary to develop methods to use thealtimetric data so that the assimilation pro-cedure includes corrections to the barotropiccontributions, as well, which play a signifi-cant role in the circulation of the coastalwaters on the continental shelf.

Since in situ measurements of ocean cur-rents are costly and time consuming to ac-quire, adequate ocean current data are prac-tically non-existent for assimilation purposes.Periodically, a few research sites may pro-vide current measurements over some re-gions but they only operate for limited peri-ods of time and thus are not suitable foroperational models. There are now plans inprogress to deploy comprehensive oceanmeasurement networks, including currents,along the coastal areas of the U.S. under theaegis of programs such as the Coastal OceanObserving System (COOS; e.g., Seim,2003). When these programs are fully es-tablished and become operational, theywould be invaluable sources of data for as-similation into, and improvement of, oceanforecast models. In the meantime, satellitefeature tracking procedures could be usedto produce ocean surface currents from theAVHRR and ocean color imagery which isnow available from a number of operationalsatellites. The feasibility of producing suchinformation on an operational basis has al-ready been established (Breaker et al., 1996).Unfortunately, however, there is no ongo-ing effort to produce surface current infor-mation from these data sources.

The availability of salinity data from di-rect measurements would be extremely help-ful in near-coastal areas. But again, there arecurrently few, if any, observations of surfacesalinity available anywhere around the worldon a realtime basis. As a result, new ap-proaches to acquiring information on salin-ity are required. Remote sensing techniquesusing microwave sensors may offer at least apartial solution to this problem (Miller etal., 1998). A second possibility is throughthe use of Color Dissolved Organic Matter(CDOM), which can be derived from ocean

color satellite data and related to salinity (see,for example, Carder et al., 1993). Althoughsuch a relationship has only been verified incertain coastal regions, and will most likelybe location-specific, it may be possible touse ocean color from Sea Viewing WideField-of-View Sensor (SeaWiFS) to derive aproxy for salinity in areas where such rela-tionships can be established and validated.When the COOS is fully implemented, sa-linity data in coastal regions around the U.S.may become available for use in EC-ROFS.

Several mathematical techniques exist forassimilating data into ocean models but theyrequire information on the error statisticsand spatial covariance structures for themodel-minus-observation increments foreach ocean parameter of interest. Unfortu-nately, this information is poorly known formost models at the present time. As a result,parallel model runs need to be initiated todetermine the sensitivity of the model to vari-ants of the default values which are presentlybeing used to represent these statistics andwhich may lead to improvements in the ex-isting assimilation procedures. Finally, theGlobal Data Assimilation Experiment(GODAE) is a project intended to makebetter use of various remotely sensed and insitu data, and to develop effective data as-similation techniques which may be of ben-efit to operational coastal circulation mod-els such as EC-ROFS in the near future(http://www.bom.gov.au/bmrc/ocean/GODAE/).

(e) Reproducing a Realistic Gulf Stream:A problem in the GS separation occurs fre-quently in the EC-ROFS off Cape Hatteras.A persistent anticyclonic meander developsjust north of the Cape centered at approxi-mately 36°N and 74°W. This problem arisesin most ocean circulation models. AlthoughSST data assimilation appears to significantlyreduce this artifact, the unrealistic meandergradually reforms when SST data are notavailable in this region for several days. Sev-eral factors may contribute to this behavior(Dengg et al., 1996). Model speeds in thecore of the GS, and also elsewhere in theGS, are usually lower than observed (up to50% lower in some cases). In the region offCape Hatteras, the 10 km spatial resolution


of the model may not be fine enough tomaintain the necessary jetlike structure.Without sufficient resolution, there may bea tendency for the Gulf Stream to spread lat-erally which could contribute to the forma-tion of the anomalous meander. The GDEMclimatology used to spin up the model doesnot contain a realistic GS, which could alsocontribute to the separation problem. Thebathymetry is very complex near CapeHatteras, and higher resolution bathymetrymay be required locally to provide the cor-rect topographic influence in this region.

(f ) Shelf Circulation in the Mid-Atlan-tic Bight: Surface flow on the continentalshelf between Cape Hatteras and Long Is-land is generally to the South (e.g., Beardsleyand Boicourt, 1981). However, as indicatedearlier, the Coastal Marine DemonstrationProject showed that EC-ROFS-generatedsurface flows in this region were generally tothe North. There are several possible expla-nations for the general lack of equatorwardflow along the shelf between Cape Hatterasand Long Island in the model. The exist-ence of an alongshore pressure gradient haslong been postulated as the primary causeof southerly flow on the shelf along the U.S.East Coast. Because the source of this along-shore pressure gradient may lie outside themodel domain, the model itself may not beresponsible for producing incorrect flowalong the shelf. However, other factors maycontribute to this problem. Buoyancy fluxesalong the east coast may be too small. Weknow, for example, that several of the lesserrivers along the East Coast are missing fromthe model, and less fresh water on the shelfmay have an impact on the cross-shelf den-sity gradient. Circulation in the cyclonic gyrethat lies in the Slope Water region betweenthe continental shelf and the GS may influ-ence the flow on the shelf itself, and the ex-pected circulation in the Slope Water regionis poorly reproduced in the model. Also,when the anomalous meander just north ofCape Hatteras is well developed, it may actto block equatorward flow along the shelf.Finally, boundary forcing along the easternboundary of the model domain may be in-correctly specified resulting in flow along theshelf which is likewise incorrect.

Concluding RemarksSome successes and a certain number of

problems have occurred during the devel-opment of EC-ROFS. Model performancenear the coast, at least in terms of water level,was found to be good because of thebarotropic nature of water level variations.Observations have verified this expectation.For some of the problems which have beenidentified, solutions or at least partial solu-tions have been found or are close at hand.Problems related to the specification of thelateral boundary conditions along the twolarge open boundaries, for example, may besignificantly reduced by prescribing morerealistic boundary conditions provided byusing a basin scale model. Replacing theexisting monthly streamflow climatologywith daily observed streamflows from theUSGS should improve predicted salinitiesand currents near the coast. In this regard,better methods need to be developed to es-timate inflows into the domain from theconnecting rivers and estuaries. As a case inpoint, there is currently no simple way toestimate the outflow from the ChesapeakeBay based on the inputs from the major riv-ers which discharge waters into the bay.

Since the availability and distribution ofoceanographic data are poor compared tothe atmosphere, increased efforts are neededto develop effective ocean data assimilationtechniques. For real time applications, theonly data types that are routinely availableare SSTs, vertical temperature profiles fromXBTs and ARGO and PALACE type floats,and altimeter data. The availability of satel-lite-derived SSTs depends on cloud cover,and the number of XBTs that are availableare usually small in number and poorly dis-tributed. The utility of altimeter data forassimilation into EC-ROFS is still open toquestion with regard to how the anomaliesin surface elevation are defined, and thespace/time coverage that is presently avail-able. Salinity data to be used for assimila-tion are very sparse and the possibility ofextracting information on salinities fromocean color satellite data is exciting andshould be pursued. The newly-developedScanning Low Frequency Microwave Radi-ometer that infers surface salinity from low-

flying aircraft should be used routinely incoastal areas around the continental U.S.where the technique can be applied. Ad-vanced three-dimensional multivariateanalysis techniques must be developed to as-similate all types of available ocean observa-tions to improve the initial conditions forEC-ROFS and similar models.

The CMDP demonstrated that forecastproducts from EC-ROFS can be used by fore-casters by taking into account certain modeldeficiencies because these deficiencies areknown and systematic in nature. This situa-tion is very similar to the atmospheric casewhere forecasters generally use the model fore-casts (with their known biases and deficien-cies) together with observations that may nothave gotten into the model and their ownexperience in producing a final forecast. Thesame approach could be used by the marinecommunity in making ocean forecasts.

The development of EC-ROFS has beena truly collaborative effort involving numer-ous individuals, groups, and organizations.The path toward operational implementa-tion has been long and at times circuitous.Further improvements in ocean model de-velopment will most likely be slow and, attimes, painful, similar to the experience inatmospheric forecast model development.Just as in the case of the early days of Nu-merical Weather Prediction, “further im-provements will be a slow and generallyunspectacular process” (Thompson, 1983).The EC-ROFS development described hereis a first step in providing real-time forecastson the physical state of the coastal ocean andin the transfer of techniques from researchto operations. Future improvements to EC-COFS will include extension of its cover-age to include all U.S. coastal areas, runningthe model every 12 hours to support opera-tional estuarine circulation models, extend-ing the model forecasts out to longer timeperiods (up to several days), and interactivecoupling to other NWP models, wave mod-els, and sea ice models. In closing, althoughEC-ROFS is still a work in progress, it be-came fully operational in March 2002, andis the first forecast system of its type to be-come operational in the civil sector of theUnited States.


AcknowledgmentsWe thank George Mellor and his col-

leagues at Princeton University, and presentand former NCEP and NOS personnel fortheir contributions to EC-ROFS. In particu-lar, we are grateful to Dmitry Sheinin andLech Lobocki for their contributions inimplementing EC-ROFS at NCEP in theearly days of this activity. Finally, fundingfrom the National Ocean Partnership Pro-gram to conduct the CMDP has given usthe opportunity to demonstrate the presentcapability in forecasting the state of thecoastal ocean.

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A UVs, Autonomous Underwater Ve-hicles, are the cutting edge of technologyused to explore the world’s oceans. Today,AUVs can explore areas of the oceans sci-entists only dreamed about mere decadesago. These robots provide unprecedentedaccess to hydrothermal vents and othermysteries of the deep. AUVs can swim un-der the polar ice caps and venture into un-derwater canyons. But scientists are not theonly group benefiting from these machines.Once the exclusive purview of the UnitedStates Navy and academic institutions, re-cent advances are bringing AUVs into thecommercial sector. AUVs can search foroffshore oil and mineral deposits, lay sub-marine cables, and search for mines. Pri-vate individuals and corporations can nowpurchase AUVs for use in salvage opera-tions, underwater archaeology, or simpleexploration. The possibilities appear limit-less and the benefits incalculable.

Unlike tethered and remotely operatedvehicles which are a simple extension of theresearch vessel, AUVs are, and legally shouldbe, considered separate entities. AUVs, asthe name suggests, are designed to operatefreely in the vast oceans. Ideally, AUVs wouldbe released and tracked from shore, elimi-nating the need for a costly support vessel.The AUV’s autonomous nature, however,creates a regulatory gap. AUVs, as discussedin more detail below, may or may not bevessels as defined by U.S. maritime laws. Theuse of AUVs is virtually unregulated by thefederal government, mostly due to a combi-nation of the newness of the technology,difficulties with classification, and the un-willingness of overburdened federal agenciesto incur additional responsibilities.

No legal framework currently exists toregulate the use of AUVs. Permits and li-censes are only required in a few narrow cir-cumstances. While there is no indication thatthe oceans are in danger of being overrunby AUVs, their growing availability andpopularity warrant investigation into thepotential regulatory implications of thewidespread use of AUVs. This commentaryexamines the current legal status of AUVsunder U.S. law and suggests that a permit-ting regime may already exist.

Technology often outpaces regulatoryregimes, whose adaptability is hindered bythe legislative process and administrativeagency resources. In general, the interna-tional treaties and domestic law governingmarine activities apply only to vessels. WhileAUVs are autonomous vehicles that oper-ate on and below the service of the ocean,the application of U.S. maritime laws, in-cluding the International Regulations forPreventing Collisions at Sea (COLREG), isunclear because these machines may not beconsidered “vessels” under U.S. law.

A vessel “includes every description ofwatercraft or other artificial contrivance used,or capable of being used, as a means of trans-portation on water.” (1 U.S.C. § 3). The “ves-sel” test is simple: is the structure “fairly en-gaged in or suitable for, commerce or navi-gation and as a means of transportation onwater?” (Hitner Sons Co. v. U.S., 13 Ct. Cust.216, 222 (1922)). For a boat, barge, or otherfloating structure to be considered a vessel,“it must have some relation to commerce ornavigation, or at least some connection witha vessel employed in trade.” (Hitner at 222).

The current AUV models have no suchconnection to commerce or navigation.

AUVs are used to study and explore theocean environment. The majority, due totheir size and design, are unable to be usedas a means of transportation for goods orpeople on water. Small AUVs used for sci-entific purposes are probably not vessels sub-ject to U.S. maritime regulations and neednot comply with the COLREGs.

Some AUVs, however, could be consid-ered vessels and would be required to com-ply with the COLREGs and other maritimelaws. For example, research is underway todevelop cargo carrying AUVs to “deliverpayloads or cargoes [sonar arrays, underwa-ter cables, scientific instruments, etc.] toplaces that manned ships or submarines can-not operator cost-effectively or safely”(Griffiths, 2003). Already the CanadianDefense Research Establishment and theU.S. Office of Naval Research have provedthat AUVs can be used to lay cables. In thespring of 1996, during a cable laying mis-sion in the Artic, the Theseus AUV laid twofibre optic cables under the polar ice cap overa distance of 175 km. (Griffiths, 2003). Theability of certain classes of AUVs to operatein commercial activities, such as laying cablesand carrying cargo, significantly alters thelegal analysis of whether AUVs are vessels.If AUVs are used to carry cargo, a strongargument can be made that they are alsovessels capable of being used for transporta-tion on the water.

So let’s assume for a moment that AUVsare vessels. One class clearly would have toadhere to the COLREG provisions—thesemi-submersibles. A semi-submersible AUVis “designed to operate like a snorkeling sub-marine and consequently, is limited to op-erations near the sea surface” (Griffiths, 2003).

A U T H O RStephanie ShowalterDirector, National Sea Grant Law Center,University of Mississippi

C O M M E N T A R Y

The Legal Status of AutonomousUnderwater Vehicles


Rule 22 of the COLREGs requires incon-spicuous, partly submerged vessels to displaya white all-round light visible up to a mini-mum of three miles. Vessels are also requiredto carry equipment for sound signals whichvaries depending on the size of the vessel. Rule33 states that vessels less than twelve meterslong are not obliged to carry the whistles andbells required on larger vessels. However, ifthe vessel is not so equipped, it must be pro-vided with some other means of making anefficient sound signal. Semi-submersibleAUVs should, therefore, also be outfitted withsome type of sound signaling device.

Unlike the semi-submersible AUVs, themajority of AUVs are designed to operatecompletely under the water. It is importantto note that the COLREGs are only appli-cable to vessels operating on the water. Thereare no lighting and signal requirements forunderwater operations, unless a vessel on thesurface is engaged in underwater operations,such as fishing or laying cables. Submarinesonly have to display lights when operatingon the surface. There may be situations,however, when the AUV might operate onthe surface. It may need to surface to sendor retrieve data or as part of its emergencyabort system. Once on the surface, the AUVwould be subject to the COLREGs.

For vessels less than twelve meters inlength, Rule 22 requires a masthead light,sternlight, and towing light visible up to twomiles; a sidelight visible up to one mile; anda white, red, green, or yellow all-round lightvisible up to two miles. For vessels more thantwelve meters long but less than fifty meterslong, a masthead light, visible up to fivemiles, is required unless the vessel is less thantwenty meters long. For vessels betweentwelve and twenty meters long, the mast-head light need only be visible for three miles.A sidelight, sternlight, towing light, and awhite, red, green or yellow all-round lightmust also be visible for a range of two miles.

Although it is unclear whether AUVs aresubject to the maritime regulations for ves-sels, to reduce damage and liability concerns,it is advisable for AUV operators to adhereto the COLREG provisions dealing withlighting and signals when the AUV is onthe surface. While an AUV may not be able

to fully comply with these requirements dueto design limitations, comparable lightingshould be incorporated into the designwhenever possible. Failure to adhere to theinternational lighting and signal require-ments may result in a maximum civil pen-alty of $5,000 which can be assessed againstboth the vessel operator and the vessel itself.Proactive engineering may facilitate compli-ance with the COLREGs and actually elimi-nate the need to determine whether an AUVis a vessel.

In addition to classification problems,questions often arise regarding whether anAUV operator needs to secure permits priorto commencing research. To reduce user con-flicts and minimize environmental impacts,a permitting regime is necessary. The foun-dations of a regime are already in place. IfAUVs are to be used in foreign waters, au-thorizations must be obtained from the for-eign nation in accordance with Part XIII ofthe UNCLOS. Researchers may also be re-quired to secure temporary export licensesthrough the Departments of State and/orCommerce for research activities in foreignwaters. In addition, federal permits are cur-rently required for AUV activities impactingthe continental shelf, conducted within amarine sanctuary, or impacting endangeredspecies or marine mammals.

Activities on the outer continental shelfand in marine sanctuaries clearly require per-mits. The waters are much murkier, however,if a researcher intends to use an AUV to ex-plore U.S. waters outside a marine sanctuaryand without contacting the continental shelf.While a researcher can restrict an AUV to aparticular area of the ocean, a researcher hasno control over whether animals enter thedesignated area during data collection. Theocean is not a static environment. Endangeredspecies and marine mammals move freely,some over great distances.

The remainder of this Commentary fo-cuses on marine mammal interactions. Be-cause of the overwhelming number of legalquestions currently surrounding the use ofAUVs, I chose to limit my Comment to adiscrete area of the law. Marine mammal in-teractions, however, are not an AUV operator’smost serious concern. An AUV is much more

likely to collide with a surface vessel or be-come entangled in a net. A longer article,which will discuss a variety of AUV legal is-sues, including vessel collisions, net entangle-ment, salvage, and liability, is currently in thedraft stages.

AUV operators do need to be aware thata regulatory regime exists to protect marinemammals from noise and harassment. If theuse of an AUV will “take” an endangered spe-cies or a marine mammal, an incidental takepermit is required from the National Oce-anic and Atmospheric Administration(NOAA) within the Department of Com-merce. An incidental take permit may be au-thorized under either the Endangered Spe-cies Act (ESA) or the Marine Mammal Pro-tection Act (MMPA). The MMPA addressesall interactions with marine mammal stocks,regardless of their endangered status.

In theory, an AUV could result in thetake of a marine mammal in violation ofthe MMPA. The MMPA defines “take” as“to harass, hunt, capture, or kill, or attemptto harass, hunt, capture, or kill any marinemammal.” While a number of worst casescenarios can be imagined, such as a marinemammal–AUV collision, it is unlikely thatan AUV will kill or directly injury a marinemammal. Most AUVs travel rather slowly,averaging about three to eight knots, whichshould allow any marine mammal plenty oftime to avoid the robot. Rather, the ques-tion is whether the operation of an AUVwould be considered harassment.

Operational noise is the most likely trig-ger for a violation of the MMPA. While theactual AUV makes very little noise, AUVsare used as sensor platforms and can beequipped with a variety of scientific instru-ments, including multi-beam echo sound-ers, side-scan sonars, and sub-bottomprofilers (Griffiths, 2003). It is this sensoryequipment, not the AUV, which would trig-ger the application of the MMPA. The im-pact of anthropogenic (human-generated)noise on marine mammals is not well docu-mented, but some preliminary studies indi-cate that marine mammal “behavior re-sponses [to noise] range from subtle changesin surfacing and breathing patterns, to ces-sation of vocalizations, to active avoidance


or escape from the region of the highestsound levels.” (National Research Council,2003). On a basic level, therefore, the noisegenerated by the surveying equipment onan AUV could potentially disrupt the be-havioral patterns of marine mammals.

Fortunately, it is not enough to simplydisrupt the behavioral patterns of marinemammals or every marine activity wouldviolate the MMPA. To rise to the level of aviolation of the MMPA, the harassmentmust involve a direct and significant intru-sion on the normal behavioral patterns of amarine mammal. Unless an AUV generatesa significant amount of noise, it is unlikelythat the use of an AUV would rise to thelevel of a direct and significant intrusion.

Precedent does exists, however, for thedelay and/or prohibition of marine researchprojects based on noise. In 2002, the Dis-trict Court for the Northern District Courtof California in Center for Biological Diver-sity v. National Science Foundation enjoinedacoustical research by the National ScienceFoundation (NSF) due to concerns over thenoise that would be generated by air guns.The testing of sonar systems by the U.S.Navy has also been delayed based on con-cerns regarding noise.

While the lack of a regulatory structurefor AUVs operations may not be high onthe federal government’s priority list, itshould be. As increasing numbers of AUVsare utilized by the private sector and researchinstitutions, user conflicts and marine mam-mal interactions are inevitable. AUV opera-tors have a right to be concerned regardingtheir potential liability in the event of anAUV malfunction or collision. While notall operators will want to obtain permits ornotify NOAA of their activities, prudentoperators may want to consider obtainingan Incidental Harassment Authorizationfrom NOAA under the MMPA.

As a general rule under the MMPA, theSecretary of Commerce may issue permitsauthorizing the taking of marine mammals.Additionally, citizens of the United Stateswho engage in a specified activity other thancommercial fishing within a specific geo-graphical region may petition the Secretaryto authorize the incidental, but not inten-

tional, taking of small numbers of marinemammals within that region. “Small take”authorizations, also known as Letters ofAuthorization (LOA), may permit the di-rect taking of marine mammals throughdeath and/or serious injury. The process tosecure a “small take” authorization is ratherlengthy. Upon receiving an application,NOAA must provide notice and an oppor-tunity for public comment and issue regu-lations setting forth permissible methods oftaking and monitoring and reporting re-quirements. Recently, the United StatesNavy utilized this provision of the MMPAto obtain a “small take” authorization for itsoperation of SURTASS LFA sonar systems.

LOAs usually involve the direct takingof marine mammals through death or seri-ous injury, and for AUV operators, the con-cern is not death or injury. Initiating theLOA process for AUV operations is not ad-visable, therefore, due both to the consider-able amount of time involved and low riskof an actual taking. In fact, because of thelow risk of serious injury or mortality andthe fact that any potential for injury or mor-tality could most likely be mitigated, an LOAis not needed. Rather, an AUV operatorshould seek an Incidental Harassment Au-thorization or IHA.

An IHA allows the incidental, but notintentional, taking of small numbers ofmarine mammals of a species or populationstock. Incidental taking means an acciden-tal taking—those takings that are infrequentor unavoidable. The National Marine Fish-eries Service defines “specified activity” as“any activity, other than commercial fish-ing, that takes place in a specified geographi-cal region and potentially involves the tak-ing of small numbers of marine mammals”

The Secretary may issue an IHA only ifhe or she finds that the harassment will havea negligible impact on such species or stockand will not have an unmitigable adverseimpact on the availability of the species orstock for subsistence uses. A “negligible im-pact” is “an impact resulting from a speci-fied activity that cannot be reasonably ex-pected to, and is not reasonably likely to,adversely affect the species or stock througheffects on annual rates of recruitment or sur-

vival.” The authorization must prescribe thepermissible methods of taking by harass-ment, measures determined by the Secre-tary to be necessary to ensure no unmitigableimpact, and monitoring and reporting re-quirements. Most importantly for appli-cants, the approval process is extremelystreamlined. Within 45 days of receiving anapplication for an IHA, the Secretary mustprovide public notice and solicit commentsfor 30 days. The Secretary is then requiredto issue the authorization, with the appro-priate conditions, within 45 days of the clo-sure of the public comment period.

For the NMFS “to consider authorizingthe taking of marine mammals incidentalto a specified activity, or to make a findingthat an incidental take is unlikely to occur,”the applicant must submit a written requestto the Office of Protected Resources and theRegional Office where the specific activityis planned. It is the above italicized languagethat indicates the IHA process could easilybe used to determine whether AUV opera-tions need permits. To date, most IHAs haveauthorized the incidental harassment ofmarine mammals through activities involv-ing noise, including sonar and seismic test-ing. The potential application of the IHAprogram, however, is quite broad.

For example, in May 2003, NOAA is-sued an IHA for construction activities inMonterey, California. The United StatesCoast Guard applied for an IHA for thepossible harassment of small numbers ofCalifornia sea lions and Pacific harbor sealsincidental to the installation of a new float-ing dock. It was estimated that as many as600 California sea lions and 20 harbor sealscould be affected by the activities at the dock.The potential effects of the constructionactivities included a temporary shift in theanimals’ hearing threshold during pile driv-ing, behavior changes, and temporary ces-sation of normal activities, such as feeding.Several mitigation measures were imposedon the Coast Guard to reduce the potentialfor harassment, including time restrictionsfor pile driving. The NMFS concluded that“while behavioral modifications, includingtemporarily vacating the haulout, may bemade by these species to avoid the resultant


visual and acoustic disturbance, this actionis expected to have a negligible impact onthe animals.”

The IHA application process is an idealavenue to force the issue of AUV regulation.Government action is too often reactionary,with agencies waiting until the activities arealready firmly entrenched before taking stepsto regulate. The IHA process is an excellentopportunity for NOAA and the industry toinvestigate the potential impacts of AUV useon marine mammals and marine habitats.Researchers and private operators concernedabout the potential impacts of AUV use onmarine mammals should seriously considerapplying for an IHA prior to their next cruise.If the agency discovers, after processing a fewIHAs for AUV operations, that the risk ofharassment is so minute that permitting isnot necessary, AUV operations can continueunimpeded. Even if NOAA determines thatharassment is likely, the benefits of securingapproval should outweigh any costs associ-ated with the additional paperwork.

Once in possession of an IHA, an indi-vidual is no longer “subject to the penaltiesunder the [MMPA] for taking by harassmentthat occurs in compliance with such autho-

rization.” Besides immunizing an operatorfrom prosecution under the MMPA for ha-rassment, an IHA could be used to alleviatethe concerns of insurers and institutionsworried about liability and user conflicts.Through the application process, a researcheror operator should discover the frequencyin which other activities are conducted inthe area. Any potential user conflicts wouldthen be avoidable, through either the vol-untary actions of the operator or the miti-gation requirements imposed by the agency.

Although a regulatory gap currently ex-ists with regard to AUVs, options are avail-able to obtain permission for AUV operationsor at least notify the appropriate federal agen-cies. By working within existing regulatoryprograms, AUV operators can work with thefederal government to make the oceans a saferplace for both humans and animals. This pro-active approach may enable the industry topostpone and even prevent regulation in thefuture, saving research institutions and op-erators valuable time and money. The wealthof data that AUVs could collect is unfathom-able. Hopefully, the use of these little robotswill continue to grow and enrich the scien-tific knowledge of the world.

ReferencesGriffiths, G. 2003. Technology and Applica-

tions of Autonomous Underwater Vehicles.

London: Taylor & Francis. 342 pp.

National Research Council. 2003. Ocean

Noise and Marine Mammals. Washington,

D.C.: National Academies Press. 204 pp.


In November 1994, Tropical Storm Gor-don stalled over the Florida Keys, wreakinghavoc on land and at sea. On the evening ofNovember 14, the tug J.A. Orgeron, adriftnear Bethel Shoal near Fort Pierce, Floridaafter experiencing engine problems, signaledthe Coast Guard for assistance. When SkipStrong, captain of the 688-foot oil-tankerCherry Valley, answered the Orgeron’s distresscall he had no way of knowing that he wasabout to make maritime salvage history bysaving the $50 million external fuel tank ofthe space shuttle Atlantis.

The story behind the rescue of the J.A.Orgeron and the barge Poseidon, which car-ried NASA’s external fuel tank, and the sub-sequent salvage claim by the owner and crewof the Cherry Valley springs to life in the ca-pable hands of Skip Strong and TwainBraden. Unfortunately, after catching thereader’s attention quickly with a tense pre-trial scene, the first fifty pages of In Peril bogsdown with an extraordinary amount of spacedevoted to the construction of the externalfuel tank and the logistics of towing it fromLouisiana to Cape Canaveral, which did notseem all that relevant to the rescue itself. InPeril, however, regains its momentum in PartII and quickly carries the reader along to itshistoric conclusion.

Although the authors assume a high levelof familiarity with nautical terms and refer-ences, In Peril, with its simple style and at-tention to detail, places the reader right inthe middle of the action. The engineers onthe Cherry Valley operate at a frantic pace,the third mate is stationed in the chartroom

By Skip Strong and Twain BradenThe Lyons Press, 2003252 pp. $22.95

Reviewed by Stephanie Showalter, DirectorSea Grant Law Center,University of Mississippi

B O O K R E V I E W

In Peril: A Daring Decision, a Captain’s Resolve,and the Salvage that Made History

ensuring that the Cherry Valley does not runaground on Bethel Shoal, and the captainsof the Cherry Valley and the J.A. Orgeron at-tempt to attach lines without endangeringtheir vessels and men while struggling withthe darkness, wind, and waves. One memo-rable passage details the first attempt of theCherry Valley’s crew to attach lines to theOrgeron using a line-throwing gun called theSpeedline 250. When the first shot sendsthe rocket soaring into the clouds instead oftoward the tug, the second attempt is critical.

“I [Captain Strong] dash backout to the wing to check our posi-tion. We are sliding past the tug butstill in range of the Speedline. Jimis set up and ready to go with an-other Speedline after confirmingwith the tug that the first one didnot reach them. He aims just overthe tug, spreads open his feet, brac-ing himself, and then pulls the trig-ger. Nothing happens. I rememberthat the instructions say to hold ontoit for a minute after pulling the trig-ger to make sure it doesn’t fire late.I can see Jim give it a fast count –nothing – before tossing the wholething over the rail into the sea.”

The story of the rescue is excitingenough, but the events that take place oncethe vessels are safe and the attorneys get in-volved are fascinating. Keystone ShippingCompany sought salvage rights from theowner of the J.A. Orgeron and NASA. De-

spite the fact that the crew of the Cherry Valleysaved NASA upwards of $50 million, thefederal government vigorously fought thesalvage award. In the end, the Fifth CircuitCourt of Appeals awarded Keystone $4.125million—the largest maritime salvage awardin U.S. history. The crew received$1,752,642, what remained after payinginterest, costs, and Keystone’s 63% share.

In Peril contains eight pages of photo-graphs, illustrations, and maps, includingnautical charts identifying the position of theCherry Valley and the Orgeron during the res-cue and tow. One page of diagrams detailingthe actual rescue is especially helpful for land-lubbers unable to visualize the rescue maneu-vers from words alone. Thoroughly enjoy-able, In Peril is an excellent selection foradrenalin junkies, history buffs, maritimelawyers, and for anyone curious about whatreally goes on during daring sea rescues.


This unique book is a “must have” foranyone designing and building pressure re-sistant underwater structures or instruments,as well as anyone designing with acrylic as astructural material. While the focus of thisbook is on acrylic structures under pressure,this highly visual 1066 page book, with over500 graphs, drawings, and photographs,provides a wealth of information about thedesign of pressure tolerant structures in gen-eral, from submarines to aquaria. Engineers,designers, manufacturers, fabricators, opera-tors, and inspectors of acrylic windows willfind this book an essential reference.

This is a deeply practical, nuts and boltsvolume filled with both detailed informa-tion and over forty years engineering wis-dom and insight into the problem of build-ing stuff that works. For example, with abasis in theoretical principles, the authorresearched, designed, and then reduced topractice the acrylic hulls for the submersiblesNEMO and Johnson Sea Links 1&2, thefirst acrylic hull submarines. Dr. Stachiw hasalso made important contributions investi-gating the use of structural ceramics for highpressure applications (see his website atwww.hydroports.com), and also remainsactive in the field of pressure vessels for hu-man occupancy (ASME PVHO).

The book was a team effort, with a won-derful historical introduction, “The quest forpanoramic vision underwater,” written byDr. Joan Stachiw. Dr. Jerry Stachiw has arefreshingly unabashed, direct style and doesnot hesitate to offer clearly stated design

By Jerry D. StachiwBest Publishing Co., 2003,1066 pp. $195.00

Reviewed by Mark Olsson, PresidentDeepSea Power & Lightand Will FormanUndersea Vehicle Consultant

B O O K R E V I E W

Handbook of Acrylics for Submersibles,Hyperbaric Chambers and Aquaria

guidelines and criteria. For example: “Thecrack-free, cyclic fatigue life of acrylic win-dows and pressure hulls in manned divingsystems is considered to be adequate if itexceeds 1000 pressure cycles of 4-hour du-ration at design pressure and temperature.”The book is well organized with a detailedtable of contents and an extensive index, al-lowing the reader to easily drill down intothis large reference and find needed specificinformation. The book also includes numer-ous references and bibliographic citations inassociation with most sections.

In his references Stachiw generously in-cludes the significant works of others thathave contributed to acrylic research and itsstructural use. Examples include AugustePiccard’s work with conical viewports insome of the first deep submersibles. He alsorefers to the significant but little knownworks of von Mises, whose graphs for cylin-drical pressure hulls have been and are stillused but seldom credited, possibly becausethey were developed prior to WWI for sub-marine hulls.

Among his accomplishments, Stachiwcompleted the impossible dream of the earlypioneer in deep submergence, AugustePiccard. At the end of his brilliant career,Piccard fantasized about a submersible witha transparent hull made up of 12 sphericalsegments to provide a panoramic view ofthe undersea. This would permit better re-search than could be done with the limitedvistas from the small viewports that he haddeveloped. After artist Bruce Beasely dem-

onstrated to the acrylic manufacturers howto cast very thick, large pieces of acrylic with-out flaws in 1969, Stachiw upgraded the 12piece Nemo hulls into 2 hemispheres for thetwo Johnson Sea Links, thus establishing thestandard of spherical pressure hull fabrica-tion used currently by virtually all acrylicdeep submersibles. Until such time as thereis a major technical breakthrough in trans-parent structural materials, this handbookwill be the bible for the designing, fabricat-ing and maintenance of acrylic pressure ves-sels and structures for human use.

The book focuses on several aspects ofacrylic window usage. The main topics cov-ered in the book are the design, fabrication,quality assurance, installation, service inspec-tion, and maintenance of pressure resistantwindows in service. Major attention is devotedto design procedure. Simple guidelines are pre-sented that facilitate the conversion of previ-ously published test data into maximum work-ing pressures by application of conversion fac-tors. For non-standard window configura-tions, a set of design stresses for service in dif-ferent ambient temperatures is suggested.

An interesting feature of the section onthe design of different window configurationsis the figures depicting the mechanism andpropagation of fracture under over-pressur-ization or pressure cycling, and the locationson the window where cracks generated bydifferent loading conditions originate. Dis-tinction is made between critical and non-critical crack locations and magnitudes.


Although traditionally acrylic compo-nents of aquaria do not fall into the categoryof pressure resistant windows, their designis very challenging, particularly for sub-merged tunnels and domes. Aquaria havecome a long way from being simple flat win-dows set in concrete. Underwater observa-tion chambers accessible by tunnels fabri-cated from plane and thermoformed acrylicplates now complement the sheer expanseof acrylic walls. Guidelines for the design,fabrication, and installation of acrylic pan-els are presented. A specification for procure-ment of acrylic castings concludes this veryinformative section.

An interesting feature of the section onfabrication is the presentation of techniquesfor the detection of residual stresses, the resultof incomplete annealing. The included tablescover the whole gamut of thermal treatmentsavailable for reduction of residual stresses in-troduced into the acrylic component by thecasting and machining procedures.

Of great help to the operator of any ves-sel equipped with acrylic windows is thedescription of environmental conditions thatcause acrylic to deteriorate. Particularly use-ful is an extensive listing of chemical com-pounds whose contact with the acrylic maybe detrimental to the optical and structuralperformance of the windows. The effect ofsubmersion in water and weathering on thedeterioration of acrylic is also noted and theireffect quantified.

One of the features of a pressure vesselfor human occupancy that generally is notcovered in other publications is the tech-niques for the illumination of the hyperbaricchamber’s interior for the benefit of occu-pants undergoing treatment. Designs oflights for illumination of the interior throughacrylic light pipes or windows are shown andtheir salient features discussed.

No book on acrylic would be completewithout a description of bonding processes.What makes the description of bonding pro-cedures in this book unusual is that it ad-dresses not only procedures for achievinggood bonds but also how to repair bad ones.

The Section on optical performance ofacrylic serves as a good introduction to op-tical effects one can expect from different

window configurations. Particular empha-sis is given to the optical effects generatedby spherical sector windows.

The book concludes with a very infor-mative description of the ANSI ASME/PVHO-1 Safety Standard covering acryliccomponents of pressure vessels. In the dis-cussion one is introduced to the origins ofthe Standard as well as its objectives and themajor technical areas it addresses. Since theauthor was one of the co-authors of the Stan-dard, his opinions expressed in this Sectionprovide a valuable insight into some of thefundamental concepts, such as design life,service life, minimum safety margin, andothers promulgated by the Standard.

It was hard in this short review to presentan account that does real justice to the con-tents and presentation of this large volume.Between the covers of this book the authorattempted to cover all facets of acrylic mate-rial, procurement, design, fabrication, instal-lation, testing, and in service inspection. Inthis endeavor he was quite successful, pre-senting the reader with both the empiricaldesign criteria and the test data from whichthey were derived.

The Marine Technology Society chosethe right publication to sponsor.


“I went aloft, and I saw in a momentsomething which I knew was the topgallantsails of a vessel. We bore away and made allthe sail we could. The wind was light, it didnot exceed a six knot breeze. I kept aloft untilI saw the topsails of the ship, and she wasseen off deck. At twelve o’clock, meridian,we was alongside of her. After we boardedher we found by her bills a cargo of £50,000sterling. She was called the Lovely Lass. Inone hour we put a Prize Master on boardher by the name of Thompson, and sent herto New Bedford, as the safest port she couldgo to.”

This sort of matter of fact, first personrecount of events during the American Revo-lutionary War by Captain Thomas Princetells the story of New England marinersduring this important chapter of our nation’shistory. This is not the story of a famousnational hero, but the story of one of themany Americans who struggled to find theirplace in the conflict, contributed to the causeand survived to tell the story. That is whatmakes this book somewhat unique. CaptainPrince’s “brief sketch of my life,” according toeditor Michael J. Crawford, is one of only adozen full autobiographical narratives bymen that served on government warshipsor privateers during the war.

Many of us have listened to the storiesand adventures of relatives and friends andhave thought that they (or we) should writedown their experiences for future generationsto experience. Captain Prince did not havechildren of his own, but his nieces and neph-ews must have listened to his stories and

Michael J. Crawford (Editor)Brassey’s, Inc., 2002223 pp. plus appendices $26.95

Reviewed by Jonathan Michael PrinceUNOLS Office, Moss Landing MarineLaboratories

B O O K R E V I E W

The Autobiography of a Yankee Mariner:Christopher Prince and the American Revolution

asked questions which most likely motivatedhim to write his memoirs. His writings werepassed down through his brother’s family fora number of generations before being tran-scribed and eventually donated to the NavalHistorical Foundation and subsequently theLibrary of Congress. The original manuscripthas been lost and the story itself might haveremained in the archives, except for the workof naval historian, Michael J. Crawford,Ph.D., the head of the Early History Branchof the Naval Historical Center. Dr. Crawfordwas drawn to Prince’s autobiography and de-cided it should be published not just becauseit was a first hand account of some impor-tant military and naval actions of the War ofIndependence, but also because it reveals theimpacts of the war on an ordinary Ameri-can. Not only does he describe the events,but also how he felt, why he made some dif-ficult choices and how these events affectedthe remainder of his life.

Crawford gives us the text of Prince’stranscribed manuscript word for word, withjust a few modifications. The manuscriptconsisted of around sixty thousand words,largely unbroken by chapter divisions orparagraph breaks. The Editor broke the workinto chapters, provided headings and intro-duced additional paragraphing along withremoving redundant and crossed out words,modernizing some spelling and punctuationand inserting explanations when needed tomake the autobiography more readable.

In addition he has made his own contri-bution to the story by providing factual in-troductions to the book and to each chap-

ter, which allows the reader to follow Prince’snarrative in the historical context. Throughthe liberal use of footnotes, Crawford pro-vides corroborating evidence for some partsof the story and corrections to others. As henotes in the introduction, a story writtenfrom memory will often include events thatare authentic, but perhaps not completelyaccurate when it comes to rememberingwhen in the sequence of events it occurredor with regards to details such as dates ornames. The Editor also provides us withnumerous maps and illustrations that en-hance the authenticity of Prince’s story. Theseare indexed just after the table of contents.A final contribution by the Editor are ap-pendices that include Captain Prince’s obitu-ary, a narrative by Ethan Allen of his captiv-ity on one of the vessels in which CaptainPrince sailed, other historical references, anda useful glossary of sailing terms.

During the course of Prince’s story weare presented with the pre-RevolutionaryWar life of a New England youth with astrong desire to follow the sea like many ofhis relatives. Succeeding in that vocation, hemoves from being a Grand Banks fishermanto being an accomplished merchant seamanin the employ of his uncle by the time thewar begins. He soon finds himself caughtup in the war as a crewmember of the sloopPolly, which was commissioned to take themembers of loyalist families from Boston toHalifax. In Halifax the ship and crew be-come prisoners of the British and are madepart of a fleet of guard ships on the St.Lawrence River. From this vantage point he


becomes personally involved in the war andwitnesses the American invasion of Canada,the imprisonment of Ethan Allen, and afterhis release from captivity, the retreat of theAmerican Army down Lake Champlain andthe Hudson River.

The American Army had been deci-mated by smallpox and, during the retreat,Captain Prince contracted the disease, butwas fortunate enough to be in New YorkCity when the effects hit him. He receivedbetter than normal care, survived and recov-ered in time to participate in attempts toprepare for the defense of New York. Hedescribes the efforts to obstruct passage upthe Hudson River by sinking several vessels.He then goes on to serve in vessels of theConnecticut Navy and finally in several pri-vateers sailing from New London. There areseveral exciting descriptions of action at seaand narrow escapes from danger.

Captain Prince concludes his story withdescriptions of his postwar life as a merchantvessel master and his growing religious con-victions—a typical Yankee mariner.

I recommend this book for anyone whohas an interest in maritime history, historyof the American Revolution or historical bi-ographies in general. It is a good and some-times exciting story that puts this importantpart of our history into the perspective of anordinary American involved in extraordinarytimes.

For me, this story brings to life the expe-riences of my ancestors. Captain Prince andI share the same emigrant ancestor; I am adirect descendant of his great, great grandfa-ther. I have seen the records of many of theseancestors that show date of birth, date ofdeath and perhaps a short sentence aboutserving on board one or more vessels, but nodetails, no insight into what their lives werelike. This volume provides that richness ofdetail for me and for many others whoseancestors made their living as seafarers in theearly years of our country. The Autobiogra-phy of a Yankee Mariner brings history to lifeand at the same time, through the efforts ofthe editor, keeps the history accurate.


J O U R N A L SHuman-generated Ocean Sound and

the Effects on Marine Life ........................... $20Ocean Observing Systems ................................ $20Science, Technology and Management in the

National Marine Sanctuary Program ............ $20Ocean Energy—an Overview of the State of

the Art ........................................................ $20Marine Archaeology and Technology—

A New Direction in Deep Sea Exploration ... $20Technology in Marine Biology ......................... $20Ocean Mapping—A Focus of Shallow

Water Environment .................................... $20Oceanographic Research Vessels ....................... $20Technology as a Driving Force in the Changing Roles

of Aquariums in the New Millennium ......... $20Submarine Telecoms Cable Installation

Technologies ............................................... $20Deep Ocean Frontiers ...................................... $20

A Formula for Bycatch Reduction .................... $16Marine Science and Technology in the Asia Region,

Part 2 ......................................................... $16Marine Science and Technology in the Asia Region,

Part 1 ......................................................... $16Major U.S Oceanographic Research Programs:

Impacts, Legacies and the Future ................. $16Marine Animal Telemetry Tags: What We Learn and

How We Learn It ........................................ $16Scientific Sampling Systems for Underwater

Vehicles ...................................................... $16U.S. Naval Operational Oceanography ............ $16Innovation and Partnerships for Marine Science and

Technology in the 21st Century .................. $16Marine Science and Technology in Russia ........ $16Public-Private Partnerships For Marine Science &

Technology (1995) ...................................... $16Oceanographic Ships (1994–95) ...................... $16Military Assets for Environmental Research

(1993–94) .................................................. $16Oceanic and Atmospheric Nowcasting and

Forecasting (1992) ...................................... $12Education and Training in Ocean Engineering

(1992) ........................................................ $12Global Change, Part II (1991–92) ................... $10Global Change, Part 1 (1991) .......................... $10

M A R I N E E D U C A T I O NEducation and Training Programs In Oceanography

and Related Fields (1995) ....................... $6Operational Effectiveness of Unmanned Underwater

Systems .................................................. $99State of Technology Report—Ocean and Coastal

Engineering (2001) ................................ $7 dom............................................................. $9For.

State of Technology Report—Marine Policy andEducation (2002) ................................... $7 dom............................................................. $9 For.

P R O C E E D I N G SOceans 2003 MTS/IEEE (CDROM) .............. $50Oceans 2002 MTS/IEEE (CDROM) .............. $50Oceans 2001 MTS/IEEE (CDROM) .............. $50

Artificial Reef Conference ................................ $25Oceans 2000 MTS/IEEE CD-ROM ............... $50Oceans 1999 MTS/IEEE ‘99 Paper Copy ........ $80Oceans 1999 MTS/IEEE CDROM ................. $40Ocean Community Conference ‘98 ............... $100Underwater Intervention 2002 ........................ $50Underwater Intervention 2000 ........................ $50Underwater Intervention ‘99 ........................... $50Underwater Intervention ‘98 ........................... $50500 Years of Ocean Exploration

(Oceans ‘97) ............................................. $130Underwater Intervention ‘97 ........................... $50The Coastal Ocean—Prospects for

The 21st Century (Oceans ‘96) ................. $145Underwater Intervention ‘96 ........................... $50Challenges of Our Changing Global

Environment (Oceans ‘95) ........................ $145Underwater Intervention ‘95 ........................... $75Underwater Intervention ‘94 ........................... $95Underwater Intervention ‘93 ........................... $95MTS ‘92 ....................................................... $140ROV ‘92 ....................................................... $105MTS ‘91 ....................................................... $130ROV ‘91 ......................................................... $951991–1992 Review of Developments in Marine

Living Resources, Engineering andTechnology ................................................. $15

ROV ‘90 ......................................................... $90The Global Ocean (Oceans ‘89) ...................... $75ROV ‘89 ......................................................... $65Partnership of Marine Interest (Oceans ‘88) ..... $65The Oceans–An International Workplace

(Oceans ‘87) ............................................... $65Organotin Symposium (Oceans ‘87, Vol. 4) ..... $10ROV ‘87 ......................................................... $40Technology Update–An International

Perspective (ROV ‘85) ................................. $35Ocean Engineering and the Environment

(Oceans ‘85) ............................................... $45Ocean Data: Sensor-to-User (1985) ................. $33Arctic Engineering for the 21st Century (1984) ..... $20Marine Salvage: Proceedings of the 3rd

International Symposium (1984) ................. $21

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UPCOMING MTS JOURNAL ISSUES

Summer 2004Innovations in Ocean Research Infrastructure toAdvance High Priority Science

Alexandra Isern—National Science Foundation

Fall 2004Environmental Threats from Submerged Vessels

Lisa Symons—NOAA

Winter 2004/2005U.S. Commission on Ocean Policy: Implicationsand Opportunities

Terry Schaff—U.S. Commission on Ocean Policy,and Dan Walker—National Research Council andOcean Studies Board

Spring 2005Acoustic Tracking of Marine Fishes: Implications forthe Design of Marine Protected Areas

James Lindholm—Pfleger Institute of EnvironmentalResearch

Summer 2005General Issue


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C O R P O R A T E M E M B E R SAlstom Power Conversion, Inc.

Houston, TexasC-Mar America, Inc.

Houston, TexasCompass Publications

Arlington, VirginiaCortland Cable Company

Cortland, New YorkDynacon, Inc.

Bryan, TexasExxonMobil Upstream Research Company

Houston, TexasFMC SOFEC Floating Inc.

Houston, TexasFugro Chance, Inc.

Lafayette, LouisianaFugro Geoservices, Inc.

Houston, TexasFugro-McClelland Marine Geosciences

Houston, TexasFugro Pelagos, Inc.

San Diego, CAGeneral Dynamics/ATS

Herndon, VirginiaGeospace Offshore Cables

Houston, TexasInnerspace Corporation

Covina, CaliforniaJ. P. Kenny, Inc.

Houston, TexasJDR Cable Systems, Inc.

Houston, TexasKlein Associations, Inc.

Salem, New HampshireKongsberg Simrad, Inc.

Houston, TexasKvaerner Oilfield Products

Houston, TexasMaritime Communication Services

Melbourne, FloridaMitsui Engineering and Shipbuilding Co. Ltd.

Tokyo, JapanMohr Engineering & Testing

Houston, TexasNautronix, Inc.

Houston, TexasNavatek, Ltd.

Honolulu, HawaiiNeptune Sciences, Inc.

Slidell, LouisianaOcean Design, Inc.

Ormond Beach, FloridaOceaneering International, Inc.

Houston, TexasOceaneering Technologies

Upper Marlboro, MarylandOil States Industries, Inc.

Arlington, TexasOrincon Hawaii, Inc.

Kailua, HawaiiPegasus International, Inc.

Houston, TexasPerry Slingsby Systems, Inc.

Jupiter, FloridaPhoenix International, Inc.

Landover, MarylandPlanning Systems, Inc.

Reston, Virginia

RD InstrumentsSan Diego, California

Reson, Inc.Goleta, California

SBM-IMODCO, INC.Houston, Texas

Schilling Robotics, LLCDavis, California

Science Applications International Corp.San Diego, California

SeaCon Brantner and Associates, Inc.El Cajon, California

Sippican, Inc.Marion, Massachusetts

Sonsub, Inc.Houston, Texas

SonTek/YSI, Inc.San Diego, California

South Bay Cable Corp.Idyllwild, California

SubConn, Inc.Burwell, Nebraska

Subsea SevenHouston, Texas

TechnipHouston, Texas

Thales Geosolutions, Inc.Houston, Texas

The Tsurumi-Seiki Co., Ltd.Yokohama, Japan

Tyco Telecommunications (US) Inc.Morristown, New Jersey

B U S I N E S S M E M B E R S4 Controlled Solutions

Houston, TexasAanderaa Instruments, Inc.

S. Attleboro, MassachusettsApplied Subsea Technologies, Inc.

Providence, Rhode IslandAshtead Technology, Inc.

Houston, TexasBennex Subsea, Houston

Houston, TexasBluewater Offshore Production Systems USA, Inc.

Houston, TexasC.A. Richards and Associates

Houston, TexasC & C Technologies, Inc.

Lafayette, LouisianaDeep Marine Technology, Inc.

Houston, TexasDeepsea Power and Light

San Diego, CaliforniaDTC International, Inc.

Houston, TexasFalmat, Inc.

San Marcos, CaliforniaGilman Corporation

Gilman, ConnecticutImpulse Enterprise

San Diego, CaliforniaInterOcean Systems, Inc.

San Diego, CaliforniaMakai Ocean Engineering, Inc.

Kailua, HawaiiMarine Desalination Systems, L.L.C.

Washington, DC

Matthews-Daniel CompanyHouston, Texas

Natural Resources CanadaDartmouth, Nova Scotia, Canada

Oceanic Imaging Consultants, Inc.Honolulu, Hawaii

OceanWorks InternationalHouston, Texas

Prizm Advanced Communication Electronics, Inc.Baltimore, Maryland

Pro Staff EngineeringHouston, Texas

Reel In, Inc.College Station Texas

Remote Ocean Systems, Inc.San Diego, California

Saipem, Inc.Houston, Texas

Sonardyne, Inc.Houston, Texas

Sound Ocean Systems, Inc.Redmond, Washington

Tension Member TechnologyHuntington Beach, California

TSC Holdings Group, Inc.Palm City, Florida

Videoray, LLCExton, Pennsylvania

Weatherguy.com, LPKailua, Hawaii

I N S T I T U T I O N A L M E M B E R SBritish Embassy

Washington, DCCEROS

Kailua-Kona, HawaiiConsortium for Oceanographic Research and Education

Washington, DCHarbor Branch Oceanographic Institution, Inc.

Fort Pierce, FloridaMBARI

Moss Landing, CaliforniaMitretek Systems

Falls Church, VirginiaNational Ocean Industries Association

Washington, D.C.NOAA/PMEL

Seattle, WashingtonNaval Facilities Engineering Service Center

Port Hueneme, CaliforniaNaval Meteorology and Oceanography Command

Stennis Space Center, MississippiScripps Institution of Oceanography

La Jolla, CaliforniaService Argos, Inc.

Largo, MarylandSW Research Institute

San Antonio, TexasU.S. Coast Guard

Washington, DCU.S. Naval Academy

Annapolis, MarylandUniversity of British Columbia Library

BC, CanadaUniversity of California Library

Berkeley, California

Marine Technology Society Member Organizations

The Marine Technology Society gratefully acknowledges the critical support of the Corporate, Business, and Institutional members listed.Member organizations have aided the Society substantially in attaining its objectives since its inception in 1963.

Marine Technology Society5565 Sterrett Place, Suite 108Columbia, Maryland 21044

Postage for periodicalsis paid at Columbia, MD,and additional mailing offices.

Documents

Marine Technology Society Journal