Orientation dependence of broadband acoustic backscattering from live squid

Abstract

A controlled laboratory experiment of broadband acoustic backscattering from live squid (Loligo pealeii) was conducted using linear chirp signals (60-103 kHz) with data collected over the full 360 of orientation in the lateral plane, in <1 increments. The acoustic measurements were compared with an analytical prolate spheroid model and a three-dimensional numerical model with randomized squid shape, both based on the distorted-wave Born approximation formulation. The data were consistent with the hypothesized fluid-like scattering properties of squid. The contributions from the front and back interfaces of the squid were found to dominate the scattering at normal incidence, while the arms had a significant effect at other angles. The three-dimensional numerical model predictions out-performed the prolate spheroid model over a wide range of orientations. The predictions were found to be sensitive to the shape parameters, including the arms and the fins. Accurate predictions require setting these shape parameters to best describe the most probable squid shape for different applications. The understanding developed here serves as a basis for the accurate interpretation of in situ acoustic scattering measurements of squid.

Hydroacoustic studies on the commercially important squid Sthenoteuthis oualaniensis in the South China Sea

“…While length is often the main factor in TS regressions, the influence of orientation and frequency on TS is greater than that of length per-unit-change (Hazen and Horne, 2003). Wide distribution in squid TS has been observed and attributed to changes in the angle of squid orientation (Kang et al, 2005;Benoit-Bird et al, 2008;Madsen et al, 2007;Lee et al, 2012). Variable purpleback flying squid behaviour may have influenced our TS values, especially given we operated with lights.…”

“…The feasibility of estimating squid stock abundance by acoustic means has been previously established (Mishima, 1951;Jefferts et al, 1987;Starr and Thorne, 1998;Goss et al, 2001;Thomas et al, 2002;Foote et al, 2006;Pecl et al, 2006;Chen et al, 2013), but information on target strength (TS) of squid is limited (Kang et al, 2005;Zhang, 2005;Madsen et al, 2007;Benoit-Bird et al, 2008;Lee et al, 2012). Zhang (2005) reported in situ TS of S. oualaniensis in the South China Sea at 38 kHz using an EK500 scientific echosounder, with squid collected by jig and a nonlinear constrained Searching Scaling Factor (SSF) algorithm used to estimate the logarithm-linear relationships between in situ TS and squid mantle length (ML).…”

“…the practical limits from experimental results; it has been widely adopted for estimating the TS of fish and zooplankton (Clay, 1992;Lavery et al, 2002). Modelling approaches have been used to derive squid TS (Mukai et al, 2000;Jones et al, 2009;Lee et al, 2012). The in situ measurements of TS provide good estimates of TS to scale integrator output, which would be directly applicable to acoustic surveys of wild populations, because in situ methods do not disturb squid or their natural behaviour (Foote et al, 1986).…”

PENGUKURAN TARGET STRENGTH DAN STOK IKAN DI PERAIRAN PULAU PARI MENGGUNAKAN METODE SINGLE ECHO DETECTOR (Measurement of Target Strength and Fish Stock in Pari Islands Seawaters Using Single Echo Detector Method)

“…Salah satu penggunaan metode akustik yang sering dilakukan adalah untuk mengestimasi densitas atau stok ikan yang ada di suatu perairan (Manik 2013). Prinsip dasar metode akustik adalah penggunaan gelombang suara yang dapat merambat jauh hingga ke dasar laut dan beberapa lapisan di bawahnya untuk mendeteksi target (Balk 2011;Lee at al. 2012;Balk dan Lindem 2014).…”

Broadband and statistical characterization of echoes from random scatterers : application to acoustic scattering by marine organisms

“…Variation of the shape of the echo pdf formed by echoes collected from different ranges of angle of orientation was also examined, and the observations were explained based on the identified backscattering mechanisms with reference to the features of the statistics of echoes from a randomly-rough prolate spheroid (Bhatia et al, submitted). The majority of material in Chapter 2, excluding the statistical analysis of squid echoes, has been published in Lee et al (2012), but additional figures are included to demonstrate consistent results from more than one experimental animal.…”