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    Anisotropy in high-frequency broadband acoustic backscattering in the presence of turbulent microstructure and zooplankton

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    JAS000670.pdf (1.948Mb)
    Date
    2012-08
    Author
    Leong, Doris  Concept link
    Ross, Tetjana  Concept link
    Lavery, Andone C.  Concept link
    Metadata
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    Citable URI
    https://hdl.handle.net/1912/5483
    As published
    https://doi.org/10.1121/1.4730904
    DOI
    10.1121/1.4730904
    Keyword
     Acoustic wave scattering; Bioacoustics; Microorganisms; Underwater sound 
    Abstract
    High-frequency broadband (120–600 kHz) acoustic backscattering measurements have been made in the vicinity of energetic internal waves. The transducers on the backscattering system could be adjusted so as to insonify the water-column either vertically or horizontally. The broadband capabilities of the system allowed spectral classification of the backscattering. The distribution of spectral shapes is significantly different for scattering measurements made with the transducers oriented horizontally versus vertically, indicating that scattering anisotropy is present. However, the scattering anisotropy could not be unequivocally explained by either turbulent microstructure or zooplankton, the two primary sources of scattering expected in internal waves. Daytime net samples indicate a predominance of short-aspect-ratio zooplankton. Using zooplankton acoustic scattering models, a preferential orientation of the observed zooplankton cannot explain the measured anisotropy. Yet model predictions of scattering from anisotropic turbulent microstructure, with inputs from coincident microstructure measurements, were not consistent with the observations. Possible explanations include bandwidth limitations that result in many spectra that cannot be unambiguously attributed to turbulence or zooplankton based on spectral shape. Extending the acoustic bandwidth to cover the range from 50 kHz to 2 MHz could help improve identification of the dominant sources of backscattering anisotropy.
    Description
    Author Posting. © Acoustical Society of America, 2012. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 132 (2012): 670-679, doi:10.1121/1.4730904.
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    • Applied Ocean Physics and Engineering (AOP&E)
    Suggested Citation
    Journal of the Acoustical Society of America 132 (2012): 670-679
     

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