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1 Swathe Services our results speak for themselves

2 Who we are Swathe Services offers: Equipment Sales Equipment Rental Experience Hydrographic Surveyors Turn-key survey support

3 Dissertation Title High Resolution Geophysical Surveying Swathe Bathymetry Performance for Mapping Underwater Archaeological Sites by James Williams Thesis Submitted to Plymouth University in partial fulfilment of the requirementsfor the degree of MSc Hydrography (In collaboration with The SHIPS Project)

4 Aims & Objectives The objective of the dissertation was to determine which type of acoustic swathe technology provides the best bathymetry performance for mapping underwater archaeological sites. It aimed to achieve this by: considering the theoretical performance of two commercially available systems; one for each type of technology, comparing field acquired data against theoretical performance, comparing results against data previously acquired through diver techniques.

5 Content 1. Introduction to swathe bathymetry systems used 2. Survey vessel setup and equipment used 3. Overview of survey location 4. Presentation of results 5. Conclusion

6 Types of System Types of Swathe Systems Multi-beam systems are called: Multi-beam Multi-beam Echo Sounder (MBES) Beam Formers Swath(e)? systems are called: Phase Measuring Bathymetric Sonar Phase Differencing Bathymetric Sonar Interferometric Multi-beam Bathymetric Side-Scan Vernier Interferometer Wide Swathe Sonar Different type of technology

7 MBES Points to remember Multi-beam manufacturers often quote a system as a 1x0.5 degree but this is only representative at NADIR. The foot print size can be calculated at any give angle by considering the: angular resolution of the system frequency of the sonar operational water depth swathe sector angle number of beams

8 Interferometry Transducer The returning acoustics wave reaches each piezoelectric element only a fraction of a second apart. Piezoelectric Elements Returning Acoustic Wave Sea Bed

9 Raw Data -MBES

10 Raw Data - Interferometry

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17 Breakwater Fort Images of structures around Plymouth Breakwater Fort (SONIC khz + POS MV)

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21 Coverage R2SONIC GS+

22 Data Density High Data Density Low Data Density

23 Positioning - Absolute

24 Positioning - Relative

25 Admiralty Salvage Pontoon

26 ASP Images GeoSwath of structures around the Plus base of Plymouth Breakwater Fort SONIC 2024 (SONIC khz + POS MV + CNAV)

27 ASP GeoSwath Plus SONIC 2024

28 ASP GeoSwath Images of structures Plus around the x1 base of line Plymouth Breakwater Fort (SONIC khz + POS MV + CNAV) GeoSwath Plus x3 Lines

29 ASP GeoSwath Plus x1 line GeoSwath Plus x3 Lines

30 RAW GS+ Data

31 QLOUD Filtering

32 Manual Processing

33 DTM Comparison GS+ (Left) vs. R2SONIC 2024 (Right) 1m DTM cell comparison

34 Blocks & Tavy Images of two hollow concrete blocks near the Plymouth Breakwater Fort (SONIC khz + POS MV + CNAV)

35 Blocks Images of two hollow concrete blocks near the Plymouth Breakwater Fort (SONIC khz + POS MV + CNAV)

36 CSWIP Images of the CSWIP structure near the Plymouth Breakwater Fort (SONIC khz + POS MV + CNAV)

37 CSWIP Images of the CSWIP structure near the Plymouth Breakwater Fort (SONIC khz + POS MV + CNAV)

38 Glaucus & Task Images of an old dive chamber and hollow tube tripod near the base of the Plymouth Breakwater Fort (SONIC khz + POS MV + CNAV)

39 Site Mapping

40 Site Mapping

41 Main Conclusions 1. The data density of the GS+ is far greater than the SONIC system, however the spread of data around the statistical mean reduces its imagery capability. 2. The SONIC system proved much better at imaging the structures around the Breakwater Fort. 3. Most of the SONIC rendered images added an extra dimension to the visualisation, with the exception of the CSWIP which lost detail in the DTM production due to the presence of more than one vertical data point at the same horizontal position. 4. The GeoSwath produced improved imaging capability when additional lines were run over the same structure. 5. The SONIC obtained 100% coverage at a 10cm cell resolution whereas the GS+ exhibited many data gaps mainly at NADIR. 6. Both systems proved capable of mapping the entire Breakwater Fort site proving their effectiveness for wide area underwater archaeological mapping to put objects on the seabed in context.

42 Thank you for your time. Questions? James Williams