Modeling low-frequency volume reverberation from fish for the February–March 1992 Gulf of Alaska surface scatter experiment

Abstract

Pelagic fish contribute to the overall level of reverberation in the near-surface ocean. At low sea states, biological reverberation can be greater than low grazing angle surface scattering and can impact the success of surface scattering experiments. This impact has been shown to occur both by model estimates of biological volume reverberation and direct measurements. Estimates of volume reverberation for the Gulf of Alaska during February–March were made using a model of swimbladder resonance applied to data on fish size, abundance, school characteristics, and vertical migratory behavior. The model reproduces features of low-frequency scattering, a characteristic resonant frequency for fish of different type, size, and depth, using parameters that influence swimbladder size and gas density. Knowledge of fish was derived from bioacoustic measurements made using fisheries sonar and information obtained from fisheries agencies. Results are compared with several direct measurements of near-surface scattering at low frequency and show that fish can impact surface scattering experiments. [Work supported by SPAWAR and ONR.]