Realistic modeling of resonant scattering from fish swimbladders

Acoustical scattering from fish is an important issue for biologists, aquaculturalists, and the military community. Their physical characteristics, behavior, and abundance can be determined by coupling acoustical measurements with accurate mathematical formulations of the scattering problem. Generally, scattering from fish is enhanced at resonance frequencies. The resonances are due to excitation of vibrational motion of the fish bladders in much the same way that bubbles resonate. Scattering from fish bladders is the central issue in determining fish resonance properties. The aim of this work is to present a mathematical/physical formulation which couples acoustical signals with realistic biophysical properties to correctly describe the acoustical scattering from fishes. Fish bladders are usually elongated and contain viscous properties in the medium surrounding the bladder. Elongation increases the resonance frequency while viscosity decreases resonance effects. A complete formulation of the problem is given by combining descriptions of scattering from deformed bubbles with spherical swimbladder models. [Work supported by ONR Technology Directorate (Element 602435N) and by the Naval Research Laboratory 6.1 Program (Element 601153N). Technical management provided by NRL-SSC.]