Vertical Uncertainty

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 USM 2004 Upper Pearl Survey

2. Vertical Uncertainty • 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) USM 2004 Upper Pearl Survey

3. Vertical Uncertainty • 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… USM 2004 Upper Pearl Survey

4. Vertical Uncertainty • Draft and Offset measurements Hare, R., Error budget analysis for NAVOCEANO hydrographic survey systems, MS, 2001. USM 2004 Upper Pearl Survey

5. Vertical Uncertainty • Refraction Post survey analysis. USM 2004 Upper Pearl Survey

6. Vertical Uncertainty • Sounder accuracy and vessel motions Manufacturer specifications USM 2004 Upper Pearl Survey

7. Vertical Uncertainty • 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 USM 2004 Upper Pearl Survey

8. Vertical Uncertainty At 1 mAt 25 m • IHO S-44 Order-1 requirement : 0.5 m 0.596 m a=0.5m b=0.013 d=1 to 25m • Total uncertainty: 0.096 m 0.221 m + DATUM TRANSFER UNCERTAINTY USM 2004 Upper Pearl Survey

9. Vertical 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. USM 2004 Upper Pearl Survey

10. Vertical Uncertainty • 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 USM 2004 Upper Pearl Survey

11. Vertical Uncertainty • TPE USM 2004 Upper Pearl Survey

12. Vertical Uncertainty • 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. USM 2004 Upper Pearl Survey

13. Vertical Uncertainty • PPK/GPS Heights needed filtering • Epochs that had sheight > 0.25m filtered, then gaps interpolated, • Furthermore, epochs that had heights > 1.5*mean(sheight) filtered iteratively until mean(sheight) < 1m USM 2004 Upper Pearl Survey

14. Vertical Uncertainty • PPK/GPS Heights Mean : -23.424 m Median : -23.768 m St.Dev. : 1.773 m Mean : -23.77 m Median : -23.786 m St.Dev. : 0.11 m 0.5m USM 2004 Upper Pearl Survey

15. Range: 5 cm Range: 2 cm Range: 33 cm Vertical Uncertainty 23 June 2004, Bertram USM 2004 Upper Pearl Survey

16. Vertical Uncertainty • 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 USM 2004 Upper Pearl Survey

17. Vertical Uncertainty • Multibeam vs. Multibeam # of points compared 1859102 Mean 0.003 Median 0.005 Std. Deviation 0.056 95% 0.109 Order 1 Error Limit 0.50 Order 1 - # Rejected 477 (99.97% ACCEPTED) Order 1 Survey ACCEPTED USM 2004 Upper Pearl Survey

18. Vertical Uncertainty • Singlebeam vs. Singlebeam # of points compared 10603 Mean 0.016 Median 0.023 Std. Deviation 0.253 95% 0.496 Order 1 Error Limit 0.51 Order 1 - # Rejected 457 (99.96% ACCEPTED) Order 1 Survey ACCEPTED USM 2004 Upper Pearl Survey

19. Vertical Uncertainty • Multibeam vs. Singlebeam # of points compared 716514 Mean -0.013 Median -0.048 Std. Deviation 0.254 95% 0.498 Order 1 Error Limit 0.51 Order 1 - # Rejected 24375 (96.6% ACCEPTED) Order 1 Survey ACCEPTED BUT… USM 2004 Upper Pearl Survey

20. Vertical Uncertainty • 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. USM 2004 Upper Pearl Survey

21. Vertical Uncertainty • 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. USM 2004 Upper Pearl Survey

22. Vertical Uncertainty • 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. USM 2004 Upper Pearl Survey

23. Processing: Horizontal Uncertainty Debbie Mabey