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Point-source violations: split-beam tracking of fish at close range

Published online by Cambridge University Press:  15 September 2000

James J. Dawson ,
Daniel Wiggins ,
Donald Degan ,
Harold Geiger ,
Deborah Hart  and
Barbara Adams
James J. Dawson
Affiliation:
BioSonics Inc., 4027 Leary Way NW, Seattle, WA 98107, USA
Daniel Wiggins
Affiliation:
BioSonics Inc., 4027 Leary Way NW, Seattle, WA 98107, USA
Donald Degan
Affiliation:
Aquacoustics Inc., 112 Charter Place, Mooresville, NC 28117, USA
Harold Geiger
Affiliation:
Alaska Department of Fish and Game, 1255 West 8 Street, P.O. Box 25526, Juneau, AK 99802-5526, USA
Deborah Hart
Affiliation:
Alaska Department of Fish and Game, 1255 West 8 Street, P.O. Box 25526, Juneau, AK 99802-5526, USA
Barbara Adams
Affiliation:
University of Alaska, Fairbanks, Department of Mathematics, Fairbanks, AK 99775-7220 USA
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Abstract

Split-beam positional estimates of fish detected in a river at close range often do not correspond to the actual position of the target. These inaccuracies create problems in determining whether a fish is moving upstream or downstream. We hypothesize that these positional estimates are degraded by two factors: size of target relative to beam diameter, and the complex scattering of the fish. These parameters create a near-field effect, within which the phase measurements of the returning echoes are corrupted. Examples of fish tracks from near and far range fish detected by a split-beam echo sounder are provided to illustrate these inaccuracies. Experimental data from tethered spheres and complex targets show increasing distortion with target complexity and proximity to the transducer.

Keywords

split-beampoint-sourcefish trackingpositional estimates
Type
Research Article
Information
Aquatic Living Resources , Volume 13 , Issue 5: Shallow Water Fisheries Sonar , September 2000 , pp. 291 - 295
Copyright
© Elsevier, Inra, Ifremer, Cemagref, Ird, Cnrs, 2000

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