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Evaluating uncertainty in measurements of fish shoal aggregate backscattering cross-section caused by small shoal size relative to beam width

Published online by Cambridge University Press:  25 July 2007

Noël Diner
Noël Diner*
Affiliation:
Ifremer Centre de Brest, BP 70, 29280 Plouzané, France
*
Verena.Trenkel@ifremer.fr
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Abstract

The aggregate backscattering cross-section, σag is the sum of backscattering cross-sections of all fish in a shoal. It is a basic acoustical parameter used for shoal description and biomass estimation. Simulations were undertaken for evaluating the impact of horizontal dimension, density, depth and beam width on measurements of σag for shoals with constant abundance. The important factor determining measurement bias is the ratio of shoal size expressed as along cross-section length relative to along ship beam width at mean shoal depth. The results show that 10 log10(σag) is underestimated by about 8 dB for a 5 m long shoal located at 200 m depth if detected by a 7° beam. A formula for correcting σag estimates for shoal sizes bigger than 1.3 times the beam width is proposed. The negative measurement bias can also be reduced by using transducers with narrower beam widths.

Keywords

BiasAccuracyAcoustic measurementsSingle beam echosounderShoal energyShoal dimension
Type
Research Article
Information
Aquatic Living Resources , Volume 20 , Issue 2 , April 2007 , pp. 117 - 121
Copyright
© EDP Sciences, IFREMER, IRD, 2007

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References

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