Measurement of multibeam sonar directivity patterns

Directivity patterns of the Simrad SM2000 multibeam echo sounder, with 90-kHz and 200-kHz operating frequencies, have been measured in a calibration sea well at the Woods Hole Oceanographic Institution. A new transducer-mounting and -rotating system was used to hold the transducer at a nominal 3-m depth. The sonar array attached to the rotator can be rotated over a 180-deg sector. By means of conventional beamforming algorithms, the azimuthal location of the calibration target was determined at different rotation angles. The incoherently averaged directivity patterns of the two multibeam systems were measured over an angular sector of -35 deg to 40 deg. The characteristics of the directivity and reverberation are discussed.