HIGH-RESOLUTION ADAPTIVE BEAMFORMING FOR 3-DIMENSIONAL ACOUSTIC IMAGING OF ZOOPLANKTON

This paper investigates the use of adaptive beamforming techniques to increase the performance of a sonar imaging system developed at the Sc ripps Institution of Oceanography to monitor the migration of zooplank ton. The original system, known as Fish Television (FTV), images a vol ume using an 8 x 8 grid of beams in elevation and azimuth. Imaging cur rently performed with the FTV system is limited by a 2-deg resolution in both azimuth and elevation. In this paper, both a conventional dela y-and-sum beamformer and a minimum variance adaptive beamformer are ev aluated for use with the FTV sonar system to increase resolution and r educe sidelobe interference. Through simulation it is shown that by us ing adaptive beamforming, the image resolution can be improved to 1/4 deg in azimuth and elevation for targets with signal-to-noise ratios o f at least 20 dB. Results using acoustic data from the Gulf of Eilat a re compared to the original images of the FTV sonar system to illustra te the improvement in resolution, accuracy, and dynamic range achieved by adaptive beamforming. (C) 1996 Acoustical Society of America.