The low‐frequency scattering action of fish schools
作者:
Joel Garrelick,
Miguel C. Junger,
Mary L. Lamberton,
期刊:
The Journal of the Acoustical Society of America
(AIP Available online 1994)
卷期:
Volume 95,
issue 5
页码: 3020-3020
ISSN:0001-4966
年代: 1994
DOI:10.1121/1.408780
出版商: Acoustical Society of America
关键词: FISHES;UNDERWATER;BACKSCATTERING;SOUND FIELDS;INHOMOGENEITY;ACOUSTIC RESONANCE;ACOUSTIC MEASUREMENTS
数据来源: AIP
摘要:
Enhanced low‐frequency scattering levels from a single fish at its swimbladder resonance and a frequency invariant return for an octave or so above have been predicted by simple monopole scattering models [Love (1977)]. These characteristics have also been measured, more or less, with fish schools [McCartney (1967)]. In this talk the ‘‘more or less’’ is explored by modeling the school as a number of monopole scatterers quasi‐randomly distributed within an ellipsoidal volume, with and without mutual scattering taken into account. The swimbladder natural frequencies themselves are also taken to be random with a uniform PDF over a finite band. For a given realization, overall returns are computed in both the frequency and time domains. Computed fluctuations in aspect are compared with those for a Gaussian amplitude distribution. The influence of mutual scattering is shown as a function of the mean free path among individual fish. Finally, it is noted that though swimbladder gas volume and bulk modulus indicate aP5/6hydrostatic pressure dependence, swimbladder natural frequencies typically vary asP1/2[Weston (1967)]. [Work sponsored by Naval Undersea Warfare Center, New London Detachment.]
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