Proper environmental reduction for attenuation in multi-sector sonars

Multibeam backscatter data represent a major seabed discrimination tool. For seafloor characterization, however, one of the most significant limitations is the absolute calibration. There are many components of this and environmental and frequency controls on the backscatter level are two of the most important ones. As many multibeam backscatter data are reduced imperfectly for attenuation, this paper examines how important it is and how consequential it is. It introduces a precise and explicit method to properly compensate given a CTD and full knowledge of specific sector frequencies used, as long as the absorption coefficient already applied is preserved. Example cases are given for two different frequencies for historical data that were imperfectly compensated and the method is demonstrated.