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- Title
Estimation and compensation models for the shadowing effect in dense fish aggregations.
- Authors
Zhao, Xianyong; Ona, Egil
- Abstract
This paper addresses the problem of acoustic “shadowing” (i.e. first-order scattering) using an heuristic approach. It is shown that the relationship between the shadow coefficient – the proportional reduction of the acoustic energy due to the shadowing effect of fish (Zhao et al., 1993) – and the apparent area backscattering coefficient of the fish is practically linear, and that the linear relationship will hold true even with inhomogeneous fish distributions. Based on this finding a simple linear model for the estimation of the σe/σ (extinction cross-section/acoustic cross-section) ratio is developed. The model applies the reference target method of Foote et al. (1992), which allows the shadow coefficient to be determined. A model is also developed for compensation of the shadowing effect. This model can also be used to deduce the maximum-detectable fish density when the σe/σ ratio is known; and the maximum-detected apparent fish density may, in turn, suggest an upper limit of the σe/σ ratio under the specific survey condition. A correction table is provided to serve as an approximate reference and a registration from a typical herring survey is shown as an example.
- Subjects
BACKSCATTERING; SCATTERING (Physics); SURVEYS; FISHES; AQUATIC animals
- Publication
ICES Journal of Marine Science / Journal du Conseil, 2003, Vol 60, Issue 1, p155
- ISSN
1054-3139
- Publication type
Article
- DOI
10.1006/jmsc.2002.1319