30 July 2004USM 2004 Upper Pearl Survey1 Vertical Uncertainty Total Propagated Error –Error budget using Excel spreadsheets created for NAVOCEANO by Rob

30 July 2004 USM 2004 Upper Pearl Survey 1

Vertical Uncertainty

• Total Propagated Error– Error budget using Excel spreadsheets

created for NAVOCEANO by Rob Hare– TPE for every sounding using CARIS HIPS

v5.4

• Cross check analyses using Fledermaus– Multi-beam vs. Multi-beam– Single-beam vs. Single-beam– Multi-beam vs. Single-beam

• PPK/Heights



• Factors taken into account for error budget calculation– Depth variation: 1-25m– Sea state: 0– River bottom slope: 2o

– Water temperature: 28o C– Salinity: 0– Vessel roll/pitch < 1o

– Maximum swath angle for EM3000: 60o (113 out of 127 beams)



• Sounding error budget– Static and dynamic draft measurement

uncertainties – Offset measurement uncertainties– Refraction errors– Sounding system limitations– Vessel motion measurement

uncertainties– Tide and vertical datum uncertainties– And…



• Draft and Offset measurements

Standard Deviation/ RMS Values


Offset Measurement (m)

0.005 -

Draft Measurement (m)

0.037

Dynamic Draft (m) 0.0130.035

SkiffBertram

Vertical Uncertainty (at 95% C.I.)


0.010

0.069

-

0.072

0.025

Hare, R., Error budget analysis for NAVOCEANO hydrographic survey systems, MS, 2001.



• Refraction



At deepest depth (~25m)

At shallowest depth (~3m)



SV Measurement (m/s) 1.500 1.500

Temporal SV Variation (m/s)

2.000 2.000

Spatial SV Variation (m/s)

insignificant insignificant

0.030


SkiffBertram


0.090 0.040 insignificant

Post survey analysis.



• Sounder accuracy and vessel motions







Sounding System Accuracy (m)

0.100 0.110 0.120 0.010 0.010 0.010

Heave (fixed) (m) 0.050 - - -

Heave (% of amplitude) 5.000 - - -

Roll (degrees) 0.020 0.030 insignificant - - -

Pitch (degrees) 0.020 insignificant insignificant - - -

SkiffBertram


0.140 0.140


Manufacturer specifications



• Tide and sounding datum uncertainties (at 95% C.I.)

– Tide gauge measurements 0.02– Datum recovery 0.04– Use of old epoch 0.02– Tidal zoning 0.03



At 1 mAt 25 m

• IHO S-44 Order-1 requirement : 0.5 m 0.596 m

a=0.5m

b=0.013d=1 to 25m

• Total uncertainty: 0.096 m 0.221 m

22 )( dba

+ DATUM TRANSFER UNCERTAINTY



• Total Propagated Error– The Fourth Edition of S-44 [IHO, 1998] recommends

that: “All soundings should be attributed with a 95% statistical error estimate for both position and depth.”

– CARIS HIPS v5.4 uses the same approach as in previously mentioned Hare Error Model and propagates the error values to grid nodes of an uncertainty surface, using the actual vessel motion, depth and slope information instead of using average values.

– The same constant values used in spreadsheets were also used in HIPS.



• Total Propagated Error– 1m grid resolution used for this survey

– The resulting grid then was exported to an ASCII file

– HIPS doesn’t have a device model for Knudsen 320 (only some multi-beam systems are supported) so TPE could only be calculated for the multi-beam survey



• TPE



• PPK/GPS Heights– PPK/GPS data was collected both on

Bertram and Skiff throughout the survey.• Alternative to classical tide measurement for

reducing the soundings to chart datum• Tie the soundings directly to the ellipsoid for

a seamless datum

– Noisy due to obstruction of trees, especially for Skiff which ran lines across the river.



• PPK/GPS Heights needed filtering– Epochs that had height > 0.25m

filtered, then gaps interpolated,– Furthermore, epochs that had heights

> 1.5*mean(height) filtered iteratively until mean(height) < 1m



• PPK/GPS Heights

23 June 2004, PPK/GPS Heights, Skiff

-35

-30

-25

-20

-15

-10

25000 30000 35000 40000 45000 50000 55000

Time (GPS seconds)

He

igh

t (m

)

Raw

Filtered


-25

-24.5

-24

-23.5

-23

-22.5

-22

25000 30000 35000 40000 45000 50000 55000

Time (GPS seconds)

He

igh

t (m

)

Raw

Filtered


-24

-23.95

-23.9

-23.85

-23.8

-23.75

-23.7

-23.65

-23.6

-23.55

-23.5

30000 31000 32000 33000 34000 35000 36000 37000 38000 39000 40000

Time (GPS seconds)

He

igh

t (m

)

Raw

Filtered

Mean : -23.424 mMedian : -23.768 mSt.Dev. : 1.773 m

Mean : -23.77 mMedian : -23.786 mSt.Dev. : 0.11 m

0.5m



Range: 33 cm

Range: 5 cm

Range: 2 cm

23 June 2004, Bertram



• Cross check analysis– Due to relatively big size of Bertram it wasn’t

possible to run systematic multibeam cross check lines,

– Main singlebeam lines served as check lines for multibeam data => ~750 cross check lines, Order-1 requirement satisfied!

– Fledermaus Cross Check Analysis tool used for the analyses,

– All soundings used for the reference DTM instead of a decimated shoal/deep biased sounding set



• Multibeam vs.

Multibeam# of points compared 1859102Mean 0.003Median 0.005Std. Deviation 0.05695% 0.109Order 1 Error Limit 0.50 Order 1 - # Rejected 477(99.97% ACCEPTED)

Order 1 Survey ACCEPTED



• Singlebeam vs.

Singlebeam# of points compared 10603Mean 0.016Median 0.023Std. Deviation 0.25395% 0.496Order 1 Error Limit 0.51Order 1 - # Rejected 457(99.96% ACCEPTED)

Order 1 Survey ACCEPTED



• Multibeam vs.

Singlebeam# of points compared 716514Mean -0.013Median -0.048 Std. Deviation 0.25495% 0.498Order 1 Error Limit 0.51Order 1 - # Rejected 24375(96.6% ACCEPTED)

Order 1 Survey ACCEPTEDBUT…



• Cross check summary (Estimated max. error (95% C.I.): 22 cm)

– MB vs. MB : 11 cm– SB vs. SB : 50 cm

• Initial cross check analysis between MB and SB datasets showed a mean offset of 25cm (SB deeper) due to– Bad channels of EM3000 transducer– Accepted Bertram as it is, no ground truth of soundings

• Did not perform bar-check on Bertram• Did not measure static draft

• This could be seen only after applying the tides because PPK/GPS heights were noisy.



• On the other hand, Skiff was calibrated daily using bar check.

• Furthermore soundings from Skiff matched to lead line measurements within 10 cm (95%)

• As a result, mean difference between the two data sets was applied as static draft to MB data.



• Lessons learned– Make sure that you thoroughly know

the equipment/software you use.– Use every possible way to ground

truth your soundings; a simple lead line measurement may be as important as a complicated patch test.

Processing: Horizontal Uncertainty

Debbie Mabey

Documents

30 July 2004USM 2004 Upper Pearl Survey1 Vertical Uncertainty Total Propagated Error –Error budget using Excel spreadsheets created for NAVOCEANO by Rob