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Common Data Set Comparison: the GeoSwath Plus Interferometric Sonar vs Beamforming Multibeam Data

Common Data Set Comparison: the GeoSwath Plus Interferometric Sonar vs Beamforming Multibeam Data. Shallow Survey 2008 Tom Hiller, Advanced Products Manager, GeoAcoustics Ltd. James Baxter, Senior Engineer, GeoAcoustics Ltd. Presentation Overview: - Collecting the GeoSwath Dataset

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Common Data Set Comparison: the GeoSwath Plus Interferometric Sonar vs Beamforming Multibeam Data

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  1. Common Data Set Comparison: the GeoSwath Plus Interferometric Sonar vs Beamforming Multibeam Data Shallow Survey 2008 Tom Hiller, Advanced Products Manager, GeoAcoustics Ltd. James Baxter, Senior Engineer, GeoAcoustics Ltd. WORLD CLASS – through people, technology and dedication

  2. Presentation Overview: • - Collecting the GeoSwath Dataset • Data Processing • The GeoSwath Data Results • Comparison Areas • Conclusions

  3. Collecting the GeoSwath Dataset

  4. GeoSwath Plus Survey of Portsmouth Harbour Survey date: week of 20th July 2008 Sonar: GeoSwath Plus 500KHz Attitude and position: POS MV with RTK GPS

  5. Vessel and mount: R/V Coastal Surveyor - Captain Ben Smith Sonar on vessel’s bow mounted - including subsea POS-MV housing

  6. The GeoSwath interferometric sonar Side scan transmit geometry Simultaneous bathymetry and amplitude data products

  7. Sonar Geometry e d c b a

  8. The GeoAcoustics GeoSwath Plus

  9. Other Equipment Used: • Boat’s bow mount • 500kHz GeoSwath Plus • RTK positioning • POSMV Attitude • POSMV Heading • Valeport Mini-SVS • Valeport SVP sensor • Tritech Echosounder • 1PPS Timing • 50Hz attitude • 10Hz position • Local tide data

  10. Line Planning Depths: 4m to 25m Side-scan search pattern (= every object has a shadow). Used 45m range setting which gave 15 pps (=7pps/side) Survey speed ~6kts = average of 2.3 pings/m In>7m depth: Processed Bathy Swath Width: 80m (40m per side) Line spacing: alternate 30m/60m In<7m depth: Processed Bathy Swath width 70m (35m per side) Line spacing: alternate 25m/50m

  11. Run Lines in 3 areas; near shore, southern and northern

  12. GeoSwath Data Processing Amplitude filtering▼Statistical filtering▼Binning Key steps:

  13. Filtering data in the shallow areas Essentially a very simple methodology: use additional information (e.g. amplitude) and information from dense local data to flag non-matching points as outliers. Outliers will not contribute to gridded depths

  14. Filtering data in the deeper areas

  15. Every point shown (10-250 in each 1m bin) 1m Gridded data

  16. Some Notes on the Ancillary Data

  17. Typical motion data (500s of data shown below) Roll 8 deg Pitch 5 deg Heave 1m

  18. SV Dips Typical SV gives 50cm corrections at swath edges

  19. Three SV Dips in same area 1 hour apart

  20. Three near shore SV Dips

  21. Changes in Sound Velocity at the head Near-Coast Line CTS001 (N-S) 2m/s Sound Velocity at the head

  22. Line CTS005 (N-S) 2m/s Sound Velocity at the head

  23. Line CTS038 (N-S) 2m/s Sound Velocity at the head

  24. Cross-Line CTS060 (E-W) 5m/s Sound Velocity at the head

  25. Sound Velocity compared to dynamic transducer depth Roll Pitch Heave Blue: Pitch (range -2.7º to +2.4º) Black: miniSVS (range 1507.3m/s to 1510.1m/s) Heave range is -0.42m 0.46m, ~5s period 1 minute of data is shown from the middle of line CT038

  26. The Survey Results

  27. The Area Covered: ~4200m x ~1250mabout 20 hours of running lines

  28. Area covered in context

  29. Looking at the Southern Area in more Detail 2km

  30. 1m contours

  31. A profile from the 1m contour

  32. The rocky coastal areas 100m

  33. 100m Near-shore detail 5cm contours, 4m deep (NW corner) to 6m deep (SE)

  34. The GeoSwath Mosaic

  35. Lots of Lobster Pots

  36. Shoals and rocks

  37. A detailed look at part of one line: centre of CT038

  38. Profile along the line (A-B): N B A m

  39. Details of the rocky section

  40. Geology details and a drag mark

  41. Edge of rocks and a flatter section

  42. Small heave artefacts in the flat area 2cm 130m profile along a ~flat part of line CTS038

  43. m Resolving Objects

  44. 3D visualisation and georeferenced mosaic overlay

  45. Data Comparisons

  46. Three data sets with (some) overlap were available • EM3002D • Reson 7125 (to ellipsoid) • GeoSwath Plus 500kHz (to tide datum) • Note that not all the data were available for comparison, see next slide.

  47. GeoSwath and EM3002 overlap Dashed box shows overlap : overlap for available 7125 data was similar

  48. Overall differences of the overlap areas • GeoSwath – EM3002D: 20cm mean difference, 6cm SD • GeoSwath – 7125: 29.48m mean difference, 7cm SD • 7125 – EM3002D: 29.28m mean difference, 5.5cm SD

  49. Notes Processing paths for EM and 7125 data unknown: supplied as 1m xyz, probably smoothed & re-gridded? 7125 was referenced to the ellipsoid. The reason for the bust between EM and GS+ data has not been tracked down yet. The following comparison images have been made after offsetting data to the same mean, for clarity. Slight positioning differences of features in the 3 datsets: grid processing effects?

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