Fish stock assessment using a horizontally steered parametric sonar

Recent concerns of over fishing and fish population depletion in the Pacific Northwest and New England Maritimes has heightened the interest and need for more accurate fish stock assessment capabilities. A novel approach for commercial fish stock assessment has been studied which uses Navy parametric sonar technology. Results of analytical modeling predict that a near-bottom parametric sonar, operating at a difference frequency of 6 kHz and steered horizontally, yields appreciable volume reverberation from physically realizable densities of fish. In turn, volume reverberation signals received on the sonar can be processed for fish density using acoustic inversion techniques. Model results for the Gulf of Maine/George's Bank environment are presented. These results reveal that under summer propagation conditions, the technique effectively isolates reverberation emanating from near-bottom distributions of fish with minimal corruption from sea-bed and sea-surface scattering mechanisms. The horizontal looking, parametric sonar has numerous advantages over conventional acoustic estimation techniques including broader areal coverage and reduced sensitivity to larval fish and plankton scattering. A notional system concept is discussed based on an existing Navy towed sonar.