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High Resolution Geophysical SurveyingHigh Resolution Geophysical Surveying

Swathe Bathymetry Performance for Mapping Swathe Bathymetry Performance for Mapping

Underwater Archaeological SitesUnderwater Archaeological Sites

Dissertation Title

bby James Williamsy James Williams

Thesis Submitted to Plymouth University in partial fulfilment of the Thesis Submitted to Plymouth University in partial fulfilment of the

requirementsrequirements for the degree offor the degree of

MScMSc HydrographyHydrography

(In collaboration with The SHIPS Project)(In collaboration with The SHIPS Project)

The objective of the dissertation was to determine which type of The objective of the dissertation was to determine which type of

acoustic swathe technology provides the best bathymetry acoustic swathe technology provides the best bathymetry

performance for mapping underwater archaeological sites.performance for mapping underwater archaeological sites.

It aimed to achieve this by:It aimed to achieve this by:

Aims & Objectives

considering the theoretical performance of two commercially considering the theoretical performance of two commercially

available systems; one for each type of technology,available systems; one for each type of technology,

comparing field acquired data against theoretical comparing field acquired data against theoretical

performance,performance,

comparing results against data previously acquired through comparing results against data previously acquired through

diver techniques.diver techniques.

1. Introduction to swathe bathymetry systems

used

2. Survey vessel setup and equipment used

3. Overview of survey location

Content

3. Overview of survey location

4. Presentation of results

5. Conclusion

Types of Swathe SystemsTypes of Swathe Systems

Multi-beam systems are called:

• Multi-beam

• Multi-beam Echo Sounder (MBES)

• Beam FormersDifferent type of

Types of System

• 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

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

MBES

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

TransducerThe returning acoustics wave reaches each piezoelectric

element only a fraction of a second apart.

Interferometry

Sea Bed

Piezoelectric Elements

Returning Acoustic Wave

Raw Data - MBES

Raw Data - Interferometry

Breakwater Fort

Images of structures around Plymouth Breakwater Fort (SONIC 2024 @400 kHz + POS MV)

Coverage

R2SONIC GS+

Data Density

High Data Density

Low Data Density

Positioning - Absolute

Positioning - Relative

Admiralty Salvage Pontoon

ASP

Images of structures around the base of Plymouth Breakwater Fort

(SONIC 2024 @400 kHz + POS MV + CNAV)GeoSwath Plus SONIC 2024

ASP

GeoSwath Plus SONIC 2024

ASP

Images of structures around the base of Plymouth Breakwater Fort

(SONIC 2024 @400 kHz + POS MV + CNAV)GeoSwath Plus x1 line GeoSwath Plus x3 Lines

ASP

GeoSwath Plus x1 line GeoSwath Plus x3 Lines

RAW GS+ Data

QLOUD Filtering

Manual Processing

DTM Comparison

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

Blocks & Tavy

Images of two hollow concrete blocks near the Plymouth Breakwater Fort

(SONIC 2024 @400 kHz + POS MV + CNAV)

Blocks

Images of two hollow concrete blocks near the Plymouth Breakwater Fort

(SONIC 2024 @400 kHz + POS MV + CNAV)

Images of the CSWIP structure near the Plymouth Breakwater Fort (SONIC

2024 @400 kHz + POS MV + CNAV)

CSWIP

Images of the CSWIP structure near the Plymouth Breakwater Fort (SONIC

2024 @400 kHz + POS MV + CNAV)

CSWIP

Glaucus & Task

Images of an old dive chamber and hollow tube

tripod near the base of the Plymouth Breakwater

Fort (SONIC 2024 @400 kHz + POS MV + CNAV)

Site Mapping

Site Mapping

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

Main Conclusions

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.

Thank you for your time.Thank you for your time.

Questions?Questions?Questions?Questions?

James WilliamsJames Williams