Comparisons among ten models of acoustic backscattering used in aquatic ecosystem research

Abstract

Analytical and numerical scattering models with accompanying digital representations are used increasingly to predict acoustic backscatter by fish and zooplankton in research and ecosystem monitoring applications. Ten such models were applied to targets with simple geometric shapes and parameterized (e.g., size and material properties) to represent biological organisms such as zooplankton and fish, and their predictions of acoustic backscatter were compared to those from exact or approximate analytical models, i.e., benchmarks. These comparisons were made for a sphere, spherical shell, prolate spheroid, and finite cylinder, each with homogeneous composition. For each shape, four target boundary conditions were considered: rigid-fixed, pressure-release, gas-filled, and weakly scattering. Target strength (dB re 1 m(2)) was calculated as a function of insonifying frequency (f = 12 to 400 kHz) and angle of incidence (θ = 0° to 90°). In general, the numerical models (i.e., boundary- and finite-element) matched the benchmarks over the full range of simulation parameters. While inherent errors associated with the approximate analytical models were illustrated, so were the advantages as they are computationally efficient and in certain cases, outperformed the numerical models under conditions where the numerical models did not converge.

Acoustic Target Strength of the Endangered Chinese Sturgeon (Acipenser sinensis) by Ex Situ Measurements and Theoretical Calculations

“…The TS of zooplankton is generally modeled as fluid-filled spheres or cylinders, while that of teleost fish has been modeled using gas-filled bubbles or cylinders [9,25]. Some models replicate anatomical details of the swimbladder and body or generalize animal morphology using combinations of regular shapes such as gas-filled and fluid-filled cylinders.…”

“…In general, the TS has been estimated using three techniques: (1) in situ measurements of free swimming in the natural habitat (i.e., in situ TS); (2) ex situ measurements of dead or live fish in a controlled environment such as a net cage (i.e., ex situ TS); and (3) theoretical or numerical backscattering models based on fish anatomy (i.e., TS model) [9,25]. The TS from a theoretical or numerical backscattering model can be examined to determine how variables such as species, body length, frequency, and orientation influence the TS values of an individual fish.…”

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)

“…Gema seperti itu dapat ditekan menggunakan single echo detector. Single echo detector merupakan alat untuk mendeteksi target tunggal dengan menguji echo-pulse dengan kriteria SED (Simmonds dan MacLennan 2005;Manik 2014;Jech 2015). Keuntungan penggunaan SED adalah dapat mengetahui lebih akurat jenis ikan yang terdeteksi oleh instrumen echosounder atau sonar.…”

Target strength of skipjack tuna (Katsuwanus pelamis) associated with fish aggregating devices (FADs)

“…Convergence was assessed with !20 nodes per wavelength. Evaluations at higher frequencies required more computer memory than was available (Jech et al, 2015).…”

“…To have a better understanding of the factors that contribute to the TS of bladderless species in general and skipjack tuna in particular, finite element models (FEM) (Jech et al, 2015) were run to predict in situ TS measurements of skipjack tuna. However, due to the paucity of published material properties for this species, the simulations were run in comparison with Atlantic mackerel, a more studied bladderless fish (Gorska et al, 2005) that was taken as a reference.…”