An experimental test of endfire synthetic aperture sonar for sediment characterisation

The validation of seafloor scattering models used for seabed characterisation requires quantifying the contributions from the sediment interface and volume to the total acoustic returns. At low-frequencies, direct measurements of sediment volume scattering have rarely been made, due to the bias in interface roughness scattering caused by large beamwidths of low-frequency sonars. Endfire Synthetic Aperture Sonar (EF-SAS) can achieve narrower beamwidths by forming a vertically oriented synthetic array as a transmitter and/or receiver and moving it through the water column. The narrower beamwidths achieved by EF-SAS allow for more accurate measurements of volume scattering by reducing interface scattering bias in acoustic returns. The application of EF-SAS for sediment characterisation is explored for the first time. The authors demonstrate that EF-SAS can be used to construct the angular response curve for both interface and volume scattering as well as to estimate the attenuation and reflection coefficients, which can be inverted for grain size.