Three-dimensional acoustic scattering models for elongated fluid-like zooplankton

Abstract

Accurate acoustic scattering models that correctly incorporate organism size, shape, material properties, and orientation are a critical component for the remote classification and detection of marine organisms, such as fish and zooplankton. Zooplankton that fall into the elongated fluid-like category are of particular importance, primarily due to their high natural abundances. In order to obtain a better understanding of the scattering properties of this class of organism, extensive laboratory measurements of the frequency (50 kHz to 1 MHz) and angular (all angles in two planes with 1-deg resolution) characteristics of the acoustic backscattering from live individual decapod shrimp (Palaemonetes vulgaris) have been performed. An acoustic scattering model based on the distorted wave Born approximation (DWBA) has been developed for these elongated fluid-like organisms. This model makes use of progressively more realistic and complex representations of the animal shape. The most sophisticated of these representations involves fully three-dimensional digitizations of the animal exterior, obtained using high-resolution computed tomography (CT). A primary focus of this study is to determine the practical conditions under which it is necessary to make use of such high-resolution, computer-intensive digitizations of animal shape.