Improving direction-sensing by multibeam sonar

The complexity of multibeam sonar systems makes their beamforming susceptible to amplitude and phase distortion, e.g., due to environmental changes. A form of calibration is usually performed in situ over a flat area to ensure flatness in the resulting sonar image. However, lack of detailed knowledge of individual channel performance prevents application of an amplitude-weighting function such as the Blackman or Hamming type, which could otherwise be used to reduce the impact of sidelobes without damaging signal quality. Two radically different solutions are proposed: application of the Vernier principle [G. Llort-Pujol, Oceans 2006 MTS/IEEE Conf. Proc. (Quebec City, Canada, 2008); C. Sintes et al., Oceans 2011 MTS/IEEE Conf. Proc. (Waikoloa, HI, 2011)] to interferometry performed at low grazing angles, and performance of a standard-target calibration [K. G. Foote et al., J. Acoust. Soc. Am. 117, 2013 (2005)] to measure the two-way sensitivity of individual channels directly. The two methods, which are also applicable to sidescan sonar, are elaborated.