Multibeam sonar calibration: target localization in azimuth

Multibeam sonar requires calibration for use in absolute backscattering measurements of water-column targets. In an initial study, a least-squares method has been developed to locate a standard calibration target in the sonar transmit plane from the individual transducer element receive signals. By enabling the target position to be specified in azimuth, the overall transmit and receive sensitivity may be measured simultaneously for a number of beams, considerably rationalizing the amount of work required for calibration by standard target. The localization technique has been applied to data derived from test measurements with the Simrad SM2000 Multibeam Echo Sounder, operating at 200 kHz, with 128 receive beams of nominal beamwidth 1.5/spl times/20 deg. The approximate root-mean-square phase mismatch is about 0.1 rad, and the resultant error of the predicted azimuth angle is less than 0.1 deg.