Raveau M, Feuillade C
Pontificia Universidad Católica de Chile, Avenida Vicuña Mackenna 4860, Santiago, Chile.
J Acoust Soc Am. 2016 Jan;139(1):163-75. doi: 10.1121/1.4939118.
The effective medium method is used to investigate resonance scattering from schools of fish with gas-filled swim bladders, as a function of frequency and azimuth. Calculations are also performed with a coupled differential equation model, which incorporates both multiple scattering between fish and wave interference interactions of their scattered fields [Feuillade, Nero, and Love, J. Acoust. Soc. Am. 99, 196-208 (1996)]. A theoretical comparison of the models for idealized spherical schools shows good agreement over the entire resonance region in the forward direction, where interference interactions have a minimal effect. Good agreement is also seen in back scattering at low frequencies, where the wavelength λ≥4s, and s is the average nearest neighbor fish separation. If λ<4s, the models diverge in back scattering, and the effective medium method fails. This can be critically important when migrations of schools to deeper water cause the collective resonance frequency to increase. Multiple scattering interactions are negligible when |4πnf(b)(2)/k|⪅0.01, where n is the fish number density, f(b) is the individual fish scattering amplitude, and k=2π/λ. A comparison with forward scattering data shows very good agreement for both models, and indicates a method for estimating fish abundance. For back scattering data, the effective medium method diverges strongly when λ<4s.
有效介质方法用于研究具有充气鱼鳔的鱼群的共振散射，作为频率和方位角的函数。还使用耦合微分方程模型进行了计算，该模型结合了鱼之间的多次散射及其散射场的波干涉相互作用[Feuillade, Nero, and Love, J. Acoust. Soc. Am. 99, 196 - 208 (1996)]。对理想化球形鱼群模型的理论比较表明，在正向整个共振区域内具有良好的一致性，在该区域干涉相互作用的影响最小。在低频后向散射中也观察到良好的一致性，其中波长λ≥4s，s是鱼的平均最近邻间距。如果λ<4s，模型在后向散射中会出现分歧，有效介质方法失效。当鱼群向更深水域迁移导致集体共振频率增加时，这可能至关重要。当|4πnf(b)(2)/k|⪅0.01时，多次散射相互作用可以忽略不计，其中n是鱼的数量密度，f(b)是单个鱼的散射幅度，k = 2π/λ。与正向散射数据的比较表明，两个模型的一致性都非常好，并表明了一种估计鱼群数量的方法。对于后向散射数据，当λ<4s时，有效介质方法会强烈发散。
