Modeling considerations for acoustic scattering by fluidlike elongated zooplankton: Model intercomparisons and recommendations for euphausiids and copepods

Abstract

Predictions of acoustic scattering by fluidlike elongated zooplankton are made using the deformed cylinder model and Distorted Wave Born Approximation over a wide range of animal size, shape, material property inhomogeneities, and orientation, as well as acoustic frequency. Each shape represents a digitized form of the shape of a euphausiid or copepod at low-, medium-, and high-resolution sampling of the shape (e.g., at low resolution, a straight smooth finite cylinder is used and at high resolution, a rough tapered bent finite cylinder is used). The results are analyzed in order to determine the conditions under which the various degrees of complexity in modeling the scattering are required. For example, the predictions illustrate that for modeling the scattering for animals near broadside incidence, relatively simple models can be used (smooth homogeneous bodies). However, for animals off broadside, which can be the case for downward-looking echosounders insonifying euphausiids and cope- pods, roughness and sometimes inhomogeneities must be used to model the scattering accurately (roughness effects dominate scattering well off broadside). Comparisons are made with laboratory data involving euphausiids, shrimp, and copepods. [Work supported by ONR.]