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Tidal and Geodetic Vertical Datums
[email protected] Geodetic Advisor,
NGSNational Ocean Service,
NOAASacramento, CA
October, 2005 Workshop
Vertical Control DatumsVertical Control Datums A set of fundamental elevations to which other elevations are A set of fundamental elevations to which other elevations are
referred.referred.
Vertical Datum TypesVertical Datum Types
AssumedAssumed – Self-explanatory – Self-explanatory
TidalTidal – Defined by observation of tidal variations over some period – Defined by observation of tidal variations over some period of time of time
(MSL, MLLW, MLW, MHW, MHHW, etc.)(MSL, MLLW, MLW, MHW, MHHW, etc.)
GeodeticGeodetic OrthometricOrthometric– Either directly or loosely based on Mean Sea – Either directly or loosely based on Mean Sea Level at one or more points at some tidal epochLevel at one or more points at some tidal epoch
(NGVD 29, NAVD 88, IGLD85, etc.)(NGVD 29, NAVD 88, IGLD85, etc.)
Types of TidesTypes of Tides
Mixed Tide
Semidiurnal Tide
Diurnal Tide
MHHMHHWW
RELATIVE SEA LEVEL CHANGE AT RELATIVE SEA LEVEL CHANGE AT SEVERAL LOCATIONS IN THE U.S.SEVERAL LOCATIONS IN THE U.S.
IDEALIZED CHANGE OF TIDAL EPOCHIDEALIZED CHANGE OF TIDAL EPOCH
1983-01 EPOCH
Tidal Datum Boundary JurisdictionsTidal Datum Boundary Jurisdictions
NAVD 88 PROGRAM DEFINITIONNAVD 88 PROGRAM DEFINITION
NAVD 88 was an initiative which combined NAVD 88 was an initiative which combined 1.1 million kilometers of leveling surveys 1.1 million kilometers of leveling surveys in the NGS National Spatial Reference in the NGS National Spatial Reference System (NSRS) database into a single least System (NSRS) database into a single least squares adjustment, to provide users with squares adjustment, to provide users with improved heights for over 500,000 vertical improved heights for over 500,000 vertical control points distributed throughout the control points distributed throughout the United States, on a common datum.United States, on a common datum.
RATIONALE FOR BASIS OF NAVD 88RATIONALE FOR BASIS OF NAVD 88
� IN ORDER TO MINIMIZE THE EFFECTS ON USGS NATIONAL IN ORDER TO MINIMIZE THE EFFECTS ON USGS NATIONAL MAPPING PRODUCTS (NMP), AS REQUESTED BY USERS, MAPPING PRODUCTS (NMP), AS REQUESTED BY USERS, NGS SELECTED THE NEW INTERNATIONAL GREAT LAKES NGS SELECTED THE NEW INTERNATIONAL GREAT LAKES DATUM OF 1985 (IGLD 85) LOCAL MEAN SEA LEVEL DATUM OF 1985 (IGLD 85) LOCAL MEAN SEA LEVEL HEIGHT VALUE AS the MINIMUM-CONSTRAINT CONTROL HEIGHT VALUE AS the MINIMUM-CONSTRAINT CONTROL POINT FOR NAVD 88. THE DATUM POINT IS LOCATED AT POINT FOR NAVD 88. THE DATUM POINT IS LOCATED AT THE MOUTH OF THE ST. LAWRENCE RIVER IN QUEBEC, THE MOUTH OF THE ST. LAWRENCE RIVER IN QUEBEC, CANADA.CANADA.
� USING FATHER POINT/RIMOUSKI AS THE DATUM POINT USING FATHER POINT/RIMOUSKI AS THE DATUM POINT FOR BOTH IGLD 85 AND NAVD 88 MINIMIZES THE IMPACT FOR BOTH IGLD 85 AND NAVD 88 MINIMIZES THE IMPACT ON NMP, AND ALLOWS NAVD 88 TO REPLACE BOTH NGVD ON NMP, AND ALLOWS NAVD 88 TO REPLACE BOTH NGVD 29 AND IGLD 55.29 AND IGLD 55.
LEVELED NETWORK FOR NAVD 88LEVELED NETWORK FOR NAVD 88
� ORIGINAL LEVELING 700,000 KMORIGINAL LEVELING 700,000 KM
� REPEAT LEVELING 200,000 KMREPEAT LEVELING 200,000 KM
� NEW NGS LEVELING 81,500 KMNEW NGS LEVELING 81,500 KM
� NEW OUTSIDE LEVELING 20,000 KMNEW OUTSIDE LEVELING 20,000 KM
� TOTAL FOR NAVD 88 1,001,500 KMTOTAL FOR NAVD 88 1,001,500 KM (620,000 MI)(620,000 MI)
NAVD 88 DATUM DEFINITIONNAVD 88 DATUM DEFINITION
� Vertical datum based upon an equipotential Vertical datum based upon an equipotential surfacesurface
� Minimally constrained adjustment held fixed Minimally constrained adjustment held fixed at Father Point (Point-au-Pere), in Rimouskiat Father Point (Point-au-Pere), in Rimouski
� 1.1 million km of leveling data used1.1 million km of leveling data used
� Heights of 585,000 permanent bench marks Heights of 585,000 permanent bench marks estimatedestimated
� Both orthometric heights and geopotential Both orthometric heights and geopotential numbers publishednumbers published
NGVD 29 TIDE CONTROLNGVD 29 TIDE CONTROL
COMPARISON OF VERTICAL COMPARISON OF VERTICAL DATUM ELEMENTSDATUM ELEMENTS
NGVD 29NGVD 29 NAVD88NAVD88
DATUM DEFINITIONDATUM DEFINITION 26 TIDE GAGES26 TIDE GAGES FATHER POINT FATHER POINT IN THE U.S. & CANADA IN THE U.S. & CANADA
QUEBEC, CANADAQUEBEC, CANADA
BENCH MARKSBENCH MARKS 100,000100,000 450,000450,000
LEVELING (Km)LEVELING (Km) 102,724102,724 1,001,500 1,001,500
GEOID FITTINGGEOID FITTING Distorted to Fit Distorted to Fit Best ContinentalBest Continental MSL GaugesMSL Gauges ModelModel
NGVD 29 versus NAVD NGVD 29 versus NAVD 8888
What is the GEOID?What is the GEOID?
• ““The The equipotential surfaceequipotential surface of the Earth’s of the Earth’s gravity field which best fits, in the least gravity field which best fits, in the least squares sense, mean sea level.”*squares sense, mean sea level.”*
• Its surface can’t be seen or measured Its surface can’t be seen or measured directlydirectly
• It is modeled from gravity dataIt is modeled from gravity data
*Definition from the Geodetic Glossary, September 1986*Definition from the Geodetic Glossary, September 1986
H
H = Orthometric Height (NAVD 88)
H = h - N
TOPOGRAPHIC SURFACE
h = Ellipsoidal Height (NAD 83)N = Geoid Height (GEOID 03)
h
EllipsoidGRS80
N
GeoidGEOID 03
EllipsoidEllipsoid,, GeoidGeoid,, andand Orthometric Orthometric HeightsHeights
Geodetic Geodetic Control Control NetworksNetworks
Northern California
CaltransObservationsLeveling Hwy 20
CaltransObservationsLeveling Hwy 20
A specific 19 year period that includes the longest periodic tidal variations caused by the astronomic tide-producing forces.
Averages out long term seasonal meteorological, hydrologic, and oceanographic fluctuations.
Provides a nationally consistent tidal datum network (bench marks) by accounting for seasonal and apparent environmental trends in sea level that affects the accuracy of tidal datums.
The NWLON provides the data required to maintain the epoch and make primary and secondary determinations of tidal datums.
NATIONAL TIDAL DATUM EPOCH
http://www.co-ops.nos.noaa.gov
Comparison of NAVD88 ‘datum’ Comparison of NAVD88 ‘datum’ from Geodetic and Tidal from Geodetic and Tidal viewpointsviewpoints
BM NAVD88 (DS) MLLW (TS) NAVD88 (TS) Geod-Tid Diff[MLLW+.043]
TIDAL 2 4.679 4.638 4.681 -0.002B 21 1919 6.619 6.578 6.621 -0.002NO 3 1933 3.724 3.682 3.725 -0.001TIDAL BM 9 7.67 7.621 7.664 0.0063450 K 1976 5.416 5.373 5.416 03450 M 1983 3.565 3.52 3.563 0.0023450 TIDAL 7 5.125 5.082 5.125 0
http://www.co-ops.nos.noaa.gov
-0.50
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
5.00
MONTEREY MOSS LANDING ENT BRIDGE MARI DOCK AT ELKHORN KIRBY PARK RR BRIDGE
Fee
t ab
ove
NA
VD
88
MSL
MHW
MLLW
0.00
SUMMARYSUMMARY
• TIDAL DATUMS are based on a phase of the tide TIDAL DATUMS are based on a phase of the tide (eg, MHW, MLLW).(eg, MHW, MLLW).
• Station datums are based on a 19 year mean Station datums are based on a 19 year mean called an National Tidal Datum Epoch (NTDE).called an National Tidal Datum Epoch (NTDE).
• Tide stations are referenced to a bench mark Tide stations are referenced to a bench mark system (NAVD 88) for stability checks & long system (NAVD 88) for stability checks & long term maintenance.term maintenance.
• Datum applications: PORTS, chart depths , Datum applications: PORTS, chart depths , marine boundaries, hydrographic surveys, marine boundaries, hydrographic surveys, nautical charting, dredging, storm surge, nautical charting, dredging, storm surge, modeling, wetland restoration, etc.modeling, wetland restoration, etc.
APPLICATIONS SUPPORTED BY APPLICATIONS SUPPORTED BY THE NATIONAL WATER LEVEL AND TIDAL THE NATIONAL WATER LEVEL AND TIDAL
CURRENT PROGRAMSCURRENT PROGRAMSFunctionFunction ApplicationApplicationNavigation/SafetyNavigation/Safety Real-Time Navigation,Real-Time Navigation,
Hydrographic Surveys, Hydrographic Surveys, Airborne Hydrography, Airborne Hydrography, HAZMAT Response ...etc.HAZMAT Response ...etc.
Environmental Assessment/Environmental Assessment/ Wetland Delineation, CoastalWetland Delineation, CoastalMonitoringMonitoring Zone Management, Enforcement, Zone Management, Enforcement,
Insurance, Storm Surge, Insurance, Storm Surge, Tsunami Warning…etc.Tsunami Warning…etc.
Basic & Applied ResearchBasic & Applied Research Modeling, Wetland Studies, Modeling, Wetland Studies, Global Warming Studies, Global Warming Studies, Sea Level Change, Estuarine/Sea Level Change, Estuarine/Hydrodynamic Studies…etc.Hydrodynamic Studies…etc.
TIDES SUPPORT TO NAUTICAL CHARTINGTIDES SUPPORT TO NAUTICAL CHARTINGHYDROGRAPHY APPLICATIONSHYDROGRAPHY APPLICATIONS
HEIGHTS HEIGHTS ARE ARE
REFERRED REFERRED TO MHWTO MHW
SOUNDINGS SOUNDINGS ARE ARE
REFERRED REFERRED TO MLLWTO MLLW
Importance of defining Importance of defining shorelineshoreline• 95,000 miles in US95,000 miles in US• Marine territorial limits, incl EEZMarine territorial limits, incl EEZ• Law passed by US Congress in 1998 Law passed by US Congress in 1998
gave NOAA explicit authoritygave NOAA explicit authority• Nautical/navigation charts demarcate Nautical/navigation charts demarcate
MHWMHW
• NGS’ shoreline products depict MLLWNGS’ shoreline products depict MLLW• Broader adoption of NOAA’s shorelines is Broader adoption of NOAA’s shorelines is
encouraged to alleviate some confusionencouraged to alleviate some confusion
Thank you for attending!Thank you for attending!
NOS, NOAANOS, NOAA
