New model of resonant acoustic scattering by swimbladder-bearing fish

Abstract

A new model of a swimbladder-bearing fish has been developed in order to provide improved predictions of the resonant frequency and acoustic cross section of such a fish. The model consists of a small spherical shell in water, enclosing an air cavity which supports a surface tension. The shell is a viscous, heat-conducting Newtonian fluid, with the physical properties of fish flesh. A comparison of the results obtained with the new model to experimental data indicates that the new model constitutes a definite improvement over previous models. The new model can predict the high values of damping and elevated resonant frequencies that previous models could not. The model appears to be most accurate for fish in which tension in the swim-bladder wall has a minor effect on resonant scattering. This includes the fish which are of interest in studies of volume reverberation and therefore, the new model should be of considerable value in such studies.

Feasibility of Acoustic Remote Sensing of Large Herring Shoals and Seafloor by Baleen Whales

“…The expected target strength of a single herring in a vertical layer is determined by parameters such as mean layer depth, shoal thickness, neutral buoyancy depth, and herring length. With mean and standard deviation of the parameters empirically determined in Reference [24] (Table 2), TS is determined using a swimbladder resonance model [31] for deep shoals as described in Appendix A. Similar analysis is performed for shallow shoals given measured constraints.…”

“…Herring target strength was determined by empirical fit to a resonance model [31] over multi-frequencies in ranges relevant to this study [24]. Thousands of baleen whale vocalizations were passively recorded and localized in the vicinity of large herring shoals and call parameters, as shown in Table 1, were determined [1,2].…”

“…Using a fish swimbladder resonance model [23,31], the expected target strength TS of a single herring in a uniform vertical layer of herring is determined from:…”

Measuring the acoustic scattering response of small groups of live fish in a laboratory tank

“…(3). This leads to a matrix equation which may be written Mv = p ; where v = {v 1 , ..., v n , ..., v N } and p = {−P 1 e iφ 1 , · · · P n e iφn , ..., P N e iφ N } are column vectors containing the steady state volume oscillation amplitudes and external fields respectively for the individual bladders, and M is an N × N matrix with elements:…”

“…In the theory of acoustic resonance scattering of a fish swim bladder developed by Love [3], a frequency dependent function for δ was introduced, to describe the damping of the acoustic resonance response due to radiative, viscous, and thermal effects.…”