Correlation of sidescan backscatter with grain size distribution of surficial seabed sediments |
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| Institution: | 1. Department of Earth and Environmental Science, Vanderbilt University, PMB 351805, 2301 Vanderbilt Place, Nashville, TN 37235-1805, USA;2. Geological Survey of Bangladesh, 153 Pioneer Road, Segunbagicha, Dhaka 1000, Bangladesh;1. College of Harbour, Coastal and Offshore Engineering, Hohai University, Nanjing, China;2. Deltares, Delft, The Netherlands;3. Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, The Netherlands;4. MOE Key Laboratory for Coast and Island Development, Nanjing University, Nanjing, China;5. Nanjing Hydraulic Research Institute, Nanjing, China;6. State Key Laboratory for Estuarine and Coastal Studies, East China Normal University, Shanghai, China;1. GEOMAR Helmholtz Center for Ocean Research, 24148 Kiel, Germany;2. Acoustics Group, Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands;3. Deltares, Princetonlaan 6, 3584 CB Utrecht, The Netherlands |
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| Abstract: | The dependence of acoustic backscatter on sediment grain size distribution is examined using dual frequency (100 and 410 kHz) sidescan sonar and 22 sediment grab samples from the Loch Linnhe artificial reef site on the west coast of Scotland. The sidescan data were processed to remove an empirically estimated average grazing angle dependence on backscatter. The processed data were analysed by forming histograms of pixels extracted from a 20 m2 box around each ground truth site. A positive correlation (r=0.73) between mean backscatter intensity and mean grain size was obtained, i.e., the coarsest samples had the brightest backscatter. A positive correlation (r=0.59) was also found between the standard deviations of the backscatter and grain size distributions, i.e., poorly sorted sediments gave the most variable backscatter. The performance of the sidescan data was compared to results from a co-incident single-beam echo-sounder RoxAnn survey. The RoxAnn roughness index E1 compared well with the sidescan, whilst the RoxAnn hardness index E2 did not. This may be due to a physical link between the acoustic measures. The comparison showed the sidescan to have delivered a significantly higher-resolution image of the seabed for a similar amount of ship-time. Imaging of the artificial reef modules themselves was found to be frequency dependent. |
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