Abstract
Schools of fish can cause interference for long-range active sonars. The degree of interference depends heavily on the target strengths of the schools. However, there are few measurements and limited modeling of school target strengths in the frequency ranges of these sonars. During the summers of 2009 through 2013, a comprehensive set of measurements of the characteristics of Pacific sardine schools was collected off the west coast of the United States. This data set has enabled model estimates of the target strength distributions of these schools to be made at frequencies between 500 Hz and 10 kHz. This paper describes the sardine school data, its use in the modeling, the modeling procedures, and the target strength distributions obtained. The analysis indicates that, given the rates at which high target strengths occurred at all frequencies of interest, Pacific sardine schools could be a significant source of interference for long-range active sonars operating in their vicinity.
Highlights
Fish are efficient scatterers of sound and, as such, they represent a source of interference for long-range active sonars, which usually operate at frequencies below 10 kHz
Large schools can produce echoes that rival those of targets
The study presented in this paper provides a general picture of scattering from compact schools at frequencies of interest to long-range active sonars. It uses an extensive set of measured Pacific sardine individual and school parameters to develop estimates of the target strength distributions of sardine schools at frequencies near and well above swimbladder resonance
Summary
Fish are efficient scatterers of sound and, as such, they represent a source of interference for long-range active sonars, which usually operate at frequencies below 10 kHz. The study presented in this paper provides a general picture of scattering from compact schools at frequencies of interest to long-range active sonars It uses an extensive set of measured Pacific sardine individual and school parameters to develop estimates of the target strength distributions of sardine schools at frequencies near and well above swimbladder resonance. These estimates are combined with information on the sardine stock to predict the potential of Pacific sardines to cause clutter or false targets at different frequencies. The paper ends with a summary of conclusions from the work
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