Target strength of some standard, and so me not - so - standard, targets in fisheries acoustics using the finite element method

The finite element method (FEM) is used to calculate target strength of standard targets in fisheries acoustics as a function of frequency and incident sound angle. These targets include spheres, spheroids, and cylinders using different boundary conditions, representing different physical properties of the scatterer. Target strength is also calculated for swimbladder models, chilean jack mackerel (Trachurus symmetricus murphyi), obtained from magnetic resonance imaging.

The target strength estimated using FEM is compared with results from other scattering models, results from the swimbladder calculations are also compared within situ measurement data. Some of the greatest advantages using numerical methods like FEM that they can be used at both low and high acoustic frequencies, can handle wide-band pulses, and with no constraints on incidence sound angle relative to the scattering object. It can also in
theory handle scattering from all parts of a fish, like its swimbladder, flesh, and bone (fluid-structure interaction). The full potential of accurate fish models from imaging techniques like MRI may be exploited using these numerical methods. The largest downside is that these types of methods are computing expensive. Comparison between the results obtained using FEM and other models shows in general good agreement.

 

Chapter 7.4