Characterization of seafloor geo-acoustic properties from multibeam data

An algorithm for the determination of seafloor geo-acoustic properties critical to high frequency sonar performance is presented in this paper together with experimental results. Determination of geo-acoustic properties is performed using data from multibeam bathymetric sonar. The criteria for evaluating the geo-acoustic properties of the seafloor are based on the shape and/or level of the angular response (AR) of seafloor reverberation. AR curves are also used to evaluate the degree of similarity between various patches of the seafloor and to produce a segmentation map (with an algorithm called SESAM). The estimation of seafloor properties is obtained using a simple model-based geo-acoustic inversion scheme to be applied on AR. The proposed approach offers at the initial stage three inversion scenarios depending on the first guess of the impedance contrast of the seabed. The scenario suitable for "harder" and "softer" seabeds is illustrated in this paper by data acquired on medium sand, gravel and on fine clay using the EM3000 multibeam system. The model used as a basis for the inversion is BORIS-SSA as it is able to handle seabed interface anisotropy, discrete scatterers, specific beam patterns and measurement geometries. It produces the actual deterministic time series which can be directly compared to signals acquired by multibeam systems at very high frequencies. The optimization of the model input parameters converges to inverted geo-acoustic parameters close to those measured in situ, such as impedance contrast, RMS roughness and scattering inclusions density