Accuracy of the Kirchhoff-Approximation and Kirchhoff-Ray-Mode Fish Swimbladder Acoustic Scattering Models

Abstract

The acoustic backscatter from pressure release prolate spheroids and a three-dimensional representation of a fish swimbladder (Chilean jack mackerel, Trachurus symmetricus murphyi) was calculated using four target strength models (Kirchhoff-approximation, Kirchhoff-ray-mode, finite element solution of the Helmholtz equation, and prolate-spheroid-modal-series). Smoothly varying errors were found in the Kirchhoff-approximation and Kirchhoff-ray-mode model results when compared to the other models, and provide objective criteria for constraining the use of the KA and KRM models. A generic correction technique is also proposed for the prolate spheroid estimates and tentatively tested on a jack mackerel swimbladder, resulting in improvements to the target strength estimates from the Kirchhoff-approximation and Kirchhoff-ray-mode models.

Wideband (15–260 kHz) acoustic volume backscattering spectra of Northern krill (Meganyctiphanes norvegica) and butterfish (Peprilus triacanthus)

“…Francis and Foote, 2003) or finite element method (e.g. Macaulay et al, 2013). Selection of appropriate analytical or numerical models depends on a number of factors, such as computing power, availability of 3D digital representations of anatomical features, and material properties (Jech et al, 2016), but scattering models are necessary for understanding the empirical spectral patterns as well as improving predictive capability for a wide variety of environmental and biological conditions that may be encountered throughout resource surveys.…”

Target strength estimates of red emperor (Lutjanus sebae) with Bayesian parameter calibration

“…Whilst this is applicable for the acoustic frequencies and species investigated here, other body parts or fine-scale details of the swimbladder or the fish shape may have a greater influence on backscatter. Model choice can have a significant effect on TS estimates (Macaulay et al 2013). Backscatter modelling remains a trade-off between computational power and model complexity.…”

Two mechanical rigs for field calibration of multi-beam fishery sonars

“…Numerous methods for computing the directivity pattern of a gas-filled swim bladder have been described in the scientific literature. Here are a few examples: Boundary Element (Cunefare et al, 1989;Fischer et al, 2004;Śmigaj et al, 2015), Kirchoff Ray -method (Clay & Horne, 1994;Peña & Foote, 2008;Horne et al, 2009;Macaulay et al, 2013), Prolate-spheroid modal -series (Stanton & Chu, 2000;Gorska & Ona, 2003;, and the Straight Cylinder (Gorska et al, 2007;.…”