The potential of inverting geo-technical and geo-acoustic sediment parameters from single-beam echo sounder returns

Abstract

Seafloor characterization is important in many fields including hydrography, marine geology, coastal engineering and habitat mapping. The advantage of non-invasive acoustic methods for sediment characterization over conventional bottom grabbing is the nearly continuous versus sparse sensing and the enormous reduction in survey time and costs. Among the various acoustic systems for seafloor characterization, the single-beam echo sounder is of particular interest due to its simplicity and versatility. Seafloor characterization algorithms can be roughly divided into two categories: model-based and empirical, where the latter simply relies on the observation that certain echo features, such as amplitude, duration and skewness of the echo, are correlated with sediment type. Here we apply the model-based approach where we compare the measured echo signal with theoretically modeled echo envelopes in the time domain. For modeling the received echo sounder signals use is made of a physical backscatter model that fully accounts for watersediment interface roughness and sediment volume scattering. We use differential evolution, a fast variant of a genetic algorithm, as the global optimization method to invert the model input parameters mean grain size, spectral strength of the interface roughness and volume scattering cross section. In the model grain size determines geo-acoustic parameters like sediment sound speed, density and attenuation. The analysis is applied to simulated data.