© 2006 International Council for the Exploration of the Sea
Using multi-angle scattered sound to size fish swimbladders
Marine Physical Laboratory, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0238, USA
*Correspondence to J. S. Jaffe: tel: +1 858 5346101; fax: +1 858 5347641. e-mail: jules{at}mpl.ucsd.edu.
Common current practice in fisheries acoustics is to use sound that has been backscattered at 180° in order to infer parameters of individual or aggregations of animals. This article proposes that there is interesting information that can be obtained by processing scatter from other observation angles. Using a simple one-dimensional model of scatter from a fish swimbladder, an expression is derived that predicts the location of the nulls of the scattered sound as a function of transmit angle, observation angle, and tilt. The model was used retrospectively to compute the size of a swimbladder from an existing data set (that of Foote, K. G. 1985. Rather-high-frequency sound scattering by swimbladdered fish. Journal of the Acoustical Society of America, 78: 688–700), with good agreement. In order to pursue the development of a pragmatic collection system, a method is suggested that uses a single transmitter with multiple receivers. The locations of the receivers can be determined using a design methodology that considers bandwidth, centre frequency, and the size of the intended object. The method ensures that a spatially unaliased backscattered waveform can be measured over a specified sampling interval. The technique is illustrated with a practical example that uses a small number of receivers, placed in the backscattered hemisphere.
Keywords: acoustic diffraction, multi-angle sound, swimbladder estimation
Received 15 June 2005; accepted 25 April 2006.
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