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Numerical modelling of broadband acoustic signatures for two Argentinian swimbladdered fish species

This work presents the first results concerning the analysis in the frequency domain of measured acoustic signatures for two swimbladdered fish species (Merluccius hubbsi and Engraulis anchoita) from the South West Atlantic Ocean. Experimental at-sea data collected off the Argentine coast, onboard the research vessel BIP V. Angelescu, is compared with numerically simulated responses by using a model based on the Boundary Element Method (BEM). The physical situation involved in the measurements (broadband signals for a frequency band spanning from 36 kHz to 85 kHz) is mathematically related to the Helmholtz differential equation which can be solved using a BEM approach considering the swimbladder as the dominant contribution to the scattering. Numerical evaluation of the acoustic response requires integration on the scattering surface (the swimbladder) which is carried out using a discretized version (mesh) of that surface obtained from X-ray computerized tomography scans. The backscattering Target Strength (TS) for each species was computed for two types of scatterers, a non-penetrable soft scatterer and a penetrable fluid scatterer. Reported comparisons between numerical and measured results in the frequency domain provide an encouraging first set of results and reveal a broad spectrum of further work in the future.