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Target strengths of Antarctic krill (Euphausia superba) at 38 and 120 kHz

Foote, Kenneth G.; Everson, Inigo; Watkins, Jonathan L.; Bone, Douglas G.
Journal article, Peer reviewed
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URI
http://hdl.handle.net/11250/108164
Date
1990
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Original version
http://dx.doi.org/10.1121/1.399282
Abstract
Encaged aggregations of live krill in good to pristine condition have been ensonified at 38 and 120 kHz. Concurrent underwater television observations of behavior resemble those made by underwater divers in naturally occurring swarms, with comparably high densities of the order of 104 animals/m3 . Mean, single-animal target strengths have been inferred from measurements of echo energy. For aggregations with mean lengths in the range [30,39] mm, the mean single-krill target strengths are in the range [–88,–83] dB at 38 kHz and [–81,–74] dB at 120 kHz. Collateral measurements on some of the same encaged specimens determined a density contrast of 1.0357±0.0067 and sound-speed contrast of 1.0279±0.0024, relative to seawater. These numbers have been used with the fluid-sphere model as stated by Greenlaw [Limnol. Oceanogr. 24, 226–242 (1979)] . Computed backscattering cross sections have been averaged over the length distributions of each measured aggregation, resulting in target strength predictions in the range [–86,–80] dB at 38 kHz and [–79,–76] dB at 120 kHz.
Description
Journal home page: http://scitation.aip.org/jasa/
Journal
The Journal of the Acoustical Society of America

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