A Prolate Spheroidal Approach for Fish Target Strength Estimation: Modeling and Measurements

The prolate spheroidal model is reexamined to simulate the backscattered target strength by a fish through coherent treatment of the swimbladder (gas-filled spheroid) and fish body (liquid-filled spheroid). The wavelength/fish size applicability range of the model is expanded via implementation of non-traditional algorithms to calculate the prolate spheroidal radial functions. Results demonstrate the relevance of including the fish body backscatter contribution and the random nature of fish behavior to obtain good agreement between model predictions and measurements. The model was tested by comparison with direct measurements of acoustic backscattering target strength of caged fish (Percichthys trucha) using a 38 kHz split-beam echosounder. Reported values of measured maximum and averaged target strength (in the intensity domain) from gadoids (bladdered fish) and mackerel (bladderless fish) were also compared with model predictions. In all cases, a good agreement was obtained when comparing simulated and measured results.