A comparison of multibeam backscatter from the SS2012 Common Dataset

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1 A comparison of multibeam backscatter from the SS2012 Common Dataset

2 Everyone wants backscatter Always there but never been used Now specified in everything Hydrographic Survey, Renewable Surveys, Oil & Gas Site Surveys They know what they want but can we deliver it? Never has there been a more frustrating technology

3 Market segments & Clients Oil & Gas -Pipeline route survey -Site survey -Pipeline inspections Renewables -Wind park surveys -Site surveys wave & tidal energy Hydrographical -Large scale IHO mapping Enviromental -Environmental impact assessment -Habitat mapping -Species Assessment Cables -Power cable route survey -Telecommunication cable survey

4 The Purpose What can each sonar provide? Backscatter Mosaic For sediment type discrimination and object detection Angular Range Analysis For sediment type characterisation Backscatter Statistics To help the process

5 Common Dataset Issues Data collection was synonymous with current general industry knowledge and practice. Where they could, all sonar data was collected at the highest frequency, even though the ARA model is known to only work up to 300 khz Power and getting settings were geared to good bathymetry, i.e. max power No ground truth data Not all areas covered by the same sonars

6 Corrections for Receiver Gain Transmit Power Transmit pulse width Spherical Spreading Attenuation in the water column Area of ensonification Beam pattern Speckle noise If it is not there then it can t be corrected!

7 Sonars Compared EM 2040 EM 3002 GeoSwath Seabat 7125 Seabat 7101 Sonic 2024 Fledermaus FMGT Processing Software

8 Previous Studies Kongsberg EM3002D - Geocoder

9 Previous Studies Kongsberg EM3002D - Geocoder

10 Differences between same model sonars Kongsberg EM3002D

11 Differences between same model sonars Kongsberg EM3002D

12 Overview

13 Kongsberg Geoswath Recorded raw data was in proprietary RDF format No full density open format data format available Sidescan type backscatter but married with the bathymetry Needing to use GeoTexture to get full benefit

14 Kongsberg Geoswath Sites Investigated HMNZS Wellington wreck site Wellington Dock

15 Kongsberg Geoswath

16 Kongsberg Geoswath HMNZS Wellington

17 Kongsberg Geoswath Barretts Reef

18 RESON Seabat 7125 Recorded raw data was in proprietary S7K format Data converted to GSF format that has correct fields for the RESON Seabat 7125 RESON systems do not output db but amplitude and the conversion between the two doesn t work very well. RESON TVG curves are non-liner so what impact this has on the steps in the grain size is not known. 35db offset applied to the data to view mosaic and create ARA values

19 RESON Seabat 7125 Sites Investigated Fresh Water Seeps HMNZS Wellington wreck site Barretts Reef

20 RESON Seabat 7125 Initial Mosaic

21 RESON Seabat 7125 Histogram showing db values after -35db offset applied

22 RESON Seabat cm Mosaic showing nadir artefact

23 RESON Seabat 7125 Statistics for mean grain size

24 RESON Seabat 7125 Initial ARA Results

25 RESON Seabat 7125 After db offset showing believable values

26 RESON Seabat 7101 Recorded raw data was in proprietary S7K format but written as a 7125 This has a fundamental affect on the processing pipeline 35db offset applied to the data to view mosaic and create ARA values

27 RESON Seabat 7101 Sites Investigated HMNZS Wellington wreck site

28 RESON Seabat 7101 Initial beam pattern view

29 RESON Seabat cm Mosaic showing nadir artefact

30 RESON Seabat m statistics Mean Grain size over HMNZS Wellington wreck

31 RESON Seabat 7101 ARA results After -25 db offset

32 R2Sonic 2024 Raw data was recorded in QINSy Latest version of QINSy now stores backscatter correctly Original DB files re-exported to correct XTF and GSF Mosaics worked fine but acoustic response curves were wrong and ARA values didn t work at all It s up to research to come up with sonar models, it should be the sonar manufacturer.

33 R2Sonic 2024 Sites Investigated Seabed Sediment area HMNZS Wellington wreck site Barretts Reef

34 R2Sonic 2024

35 R2Sonic 2024 R2Sonic 10cm Mosaic

36 R2Sonic 2024 Power or gain steps

37 R2Sonic 2024 Seabed Sediment Area

38 ARA Results HMNZS Wellington Wreck R2Sonic 2024

39 Kongsberg EM2040 Recorded raw data was recorded in Kongsberg SiS and stored in their *.all file format Dual ping capability not ready yet so not used but for other Kongsberg multi-ping sonars, the second ping has issues. *.all format contains xyz and backscatter so can be used in realtime, though tidal issues affect the slope compensation Pages and pages of documented corrections

40 Kongsberg EM2040 Sites Investigated Seabed Sediment area HMNZS Wellington wreck site Barretts Reef

41 Kongsberg EM2040 HMNZS Wellington Wreck 10cm mosaic

42 Kongsberg EM2040 HMNZS Wellington Wreck ARA results

43 Kongsberg EM2040 Seabed Sediment Area

44 Kongsberg EM2040 Fine Sand computed correctly

45 Kongsberg EM2040 Rocky areas not discerned

46 Conclusions Kongsberg GeoSwath Hard to compare as no GeoTexture over overlapping areas GeoTexture is an unknown process It does produce results though but in this presentation there is no way of verify them

47 Conclusions RESON Seabat 7125 & 7101 Much, much more work to be done TVGs are not linear, making correction difficult Ensuring correct data recorded needs much more talking with software companies

48 Conclusions R2Sonic 2024 Promises much but comes up short ARA does not work at all Ensuring correct data recorded needs much more talking with software companies

49 Conclusions Kongsberg EM2040 Excellent results ARA works for all of the Kongsberg range of sonars All the correct information is always recorded in the *.all files

50 Thank you Any questions MEASURE THE DIFFERENCE! Duncan Mallace