Superspheroidal modeling of resonance scattering from elongated air bubbles and fish swim bladders

Abstract

The extended boundary condition technique of Waterman [J. Acoust. Soc. Am. 45, 1417-1429 (1969)] has been used to make accurate studies of the frequency and azimuthal scattering distributions from extended axisymmetric acoustic objects. These objects are formed using the mathematical function for a "superellipse" [i.e., (x/a)(s) + z/b)(s) = 1, where s = 2n, n = 1,2,[ellipsis (horizontal)]], and revolving around the z-axis. For s = 2, the object is a spheroid with aspect ratio α = b/a. As s increases, the shape of the object approaches a right circular cylinder of diameter 2a and length 2b. The method is applied to the case of prolate (i.e., α > 1) air-filled objects in water, which has importance for the interpretation of acoustic scattering from oceanic objects such as air-bubbles, the swim bladders of some fish, and zooplankton. It is found that the resonance frequency increases with α, essentially as predicted using a different method by Weston, and increases in a relatively minor way with s. The resonance peak amplitude, and Q, are also more sensitive to changes in α, than s. The method shows that the monopole resonance continues to dominate low frequency scattering, leading to an almost spherically symmetric azimuthal scattering distribution, even for elongated, cylindrical, air-filled, objects with an aspect ratio up to α = 20, and s = 32.

Sound extinction by fish schools: Forward scattering theory and data analysis

“…25 The shape of swim bladders typically approximates that of a prolate spheroid, which is a 3-D object generated by rotating an ellipse 180 around its major axis. Assuming it is a prolate spheroid, Weston 16 proposed a correction factor for the resonance frequency due to nonsphericity.…”

“…Scattering due to a single fish The use of spherical "bubble-like" models has been a popular approach for describing resonance scattering from swim bladder bearing fish, 24 since the monopole action dominates the low-frequency scattering response, and the scattered field distribution has a strong spherical symmetry, even for highly elongated swimbladders. 25 This has lead to the extensive use of a theory for scattering from bubbles 26,27 in which the resonance response of the bubble is obtained by solving the "mass-spring" secondorder differential equation…”

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)

“…Metode akustik sangat efisien dan efektif digunakan dalam survei hidrografi, baik untuk keperluan eksplorasi sumberdaya laut maupun pencarian target tertentu (Manik 2012;Feuillade 2012;Baik 2013). Salah satu penggunaan metode akustik yang sering dilakukan adalah untuk mengestimasi densitas atau stok ikan yang ada di suatu perairan (Manik 2013).…”

Rayleigh scattering of a cylindrical sound wave by an infinite cylinder

“…[1][2][3][4][5] However, knowledge of the full Green's functions is necessary for many problems of current interest for which the physical spacing between the scatterers themselves or the scatterers' separation from a source or boundary is comparable to their size. In underwater acoustics, such problems can arise in dense multi-scatterer configurations, 6 radiation by finite sources, [7][8][9][10] target classification, [11][12][13] source localization, 14 scattering suppression, 15,16 and when calculating the radiation and scattering of sound due to objects located near the ocean surface 17,18 or the seafloor. [19][20][21] No simple analytic solutions are readily available for such problems, and numerical methods have to be used.…”