Image amplitude calibration and processing for seafloor mapping sonars

In seafloor-mapping applications, the measurement of backscattering strength is an important issue for sediment type identification. Unfortunately sonar systems (sidescan sonars and multibeam echosounders) usually do not feature such a functionality at the expected level of accuracy; it is then the user´s responsibility to apply corrective post-processing in order to retrieve exploitable values. In this paper are first recalled the various causes of echo level biasing bound to the sonar characteristics (directivity patterns, TVG law). Then we present the processing steps needed to retrieve accurate backscattering strength values. Finally results of innovating image filtering are presented, making clear that after appropriate processing, amplitude resolutions better than 1 dB can be expected.