OS-CFAR detection of targets in the water column and on the seafloor with a multibeam echosounder

Ordered statistic constant false alarm rate (OS-CFAR) detection is applied to the beamformed output of a multibeam echosounder to obtain estimates of the signal-to-clutter ratio across all angles at each range increment or time slice. Assuming proper compensation for transmission losses due to spreading and absorption of acoustic energy in the water column, a threshold is chosen to detect echoes in the water column above and close to the bottom, with minimal masking due to bottom echoes appearing in the sidelobes of other beams at the same range. Results are demonstrated with a multibeam echosounder operating at a single frequency of 160 kHz for all beams. This technique obviates the need for more sophisticated multibeam echosounders that avoid sidelobe masking by transmitting and receiving at different acoustic frequencies in neighboring beams.