Physics-based inversion of multi-beam echo sounder data for seafloor properties

Abstract

This is an extension of work on physics-based seafloor inversion for seafloor properties, pioneered by Pouliquen and Lurton and by Sternlicht and De Moustier. This approach fits model time series for backscattered intensity to data, with the best-fit model parameters constituting the inversion output. In the present case, use of multi-beam sonar provides a large number of time series and consequent stronger constraints on model parameters. The method has been tested at two experiment sites, one with sandy and shelly areas and one with a thin layer of mud over sand. Ground truth data were gathered on seafloor roughness using a laser line scanner, on layering using a conductivity probe, on grain-size distribution using diver cores, and on sediment sound-speed and attenuation using acoustic probes. The inversion process involves three stages. First, a sonar-equation model is used to generate echo intensity time series including scattering by both seafloor roughness and volume heterogeneity. Model-data fit provide estimates of acoustic attenuation, volume scattering strength, and interface scattering strength. Next, physics-based models are fitted to the interface and volume scattering strengths, and finally, regression relations are used to provide a set of geoacoustic parameters sufficient to constrain standard reverberation simulations. [Work supported by SERDP.]