ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

2aAO4. Analysis of rather high-frequency sound echoes from ensembles of fish.

C. S. Clay

Dept. of Geology and Geophys., Univ. of Wisconsin-Madison, 1215 W. Dayton St., Madison, WI 53706

John K. Horne

State Univ. of New York at Buffalo, Buffalo, NY 14222-1095

At rather high fequencies, fish length/wavelength ratios are in the range 1 to 20 and the majority of scattered sound originates at the swimbladder. The sonar frequency, shape, and tilt of the swimbladder affect echo amplitudes. Echo amplitudes also depend on the position of a fish in the sonar beam. Echo emplitudes can be corrected for range and position in the sonar beam, but are still dependent on sonar frequency and swimbladder orientation relative to the soundwave front. Acounstic fish models were used to examine the dependence of echo amplitudes on frequency and swimbladder orientation [C. S. Clay and J. K. Horne, J. Acoust. Soc. Am. 96, 1661--1669 (1994)]. Probability density functions (PDF) of echo amplitudes were computed for sets of fish orientation angles. The PDFs of single and ensembles of fish were sensitive to sonar frequency and fish orientation. These PDFs are more interesting than those of Rayleigh and Rice and give additional data to characterize fish targets. [Work supported in part by the NSF (OCE-8817171, OCE-9115740) and Office of Naval Research (N-00014-89-J-1515).]