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  • Comparative Studies. Non-European Languages/Literatures  (4)
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  • Comparative Studies. Non-European Languages/Literatures  (4)
RVK
  • 1
    Online Resource
    Online Resource
    Spatial coherence in range-dependent shallow water environments
    Acoustical Society of America (ASA) ; 1998
    In:  The Journal of the Acoustical Society of America Vol. 103, No. 5_Supplement ( 1998-05-01), p. 2856-2856
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 103, No. 5_Supplement ( 1998-05-01), p. 2856-2856
    Abstract: In this presentation, effects of small random fluctuations on the spatial coherence of the sound field in shallow water with multilayered sediments will be examined. These fluctuations occur within the water volume and the sediment layers as well as at the layer interfaces. Most previous work has dealt with either range-independent or weakly range-dependent environments with random variabilities. However, strong range dependence often occurs in sound-speed profiles and at layer interfaces. For example, the region of the ACT III experimental series in the Straits of Korea shows range variability arising from sloping bathymetry and a coastal front. Consequently, spatial coherence for range-dependent waveguides with small random fluctuations will be treated. Numerical simulations of the coherence function will be presented. Results will be compared with coherence lengths of the field extracted from ACT III data.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.422003
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1998
    detail.hit.zdb_id: 1461063-2
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    Online Resource
  • 2
    Online Resource
    Online Resource
    Environmental effects on frequency behavior of modal attenuation coefficients for sandy bottoms
    Acoustical Society of America (ASA) ; 2008
    In:  The Journal of the Acoustical Society of America Vol. 123, No. 5_Supplement ( 2008-05-01), p. 3594-3594
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 123, No. 5_Supplement ( 2008-05-01), p. 3594-3594
    Abstract: The modal attenuation coefficients (MACs) can be determined using a recent simplification of Biot theory [A.D. Pierce et al., J. Acoust. Soc. Am. 114, 2345 (2003)]. Numerical calculations use sandy bottom sediments and isospeed, linear, and piecewise linear water profiles, which are simplifications that preserve key features of those obtained in experiments off the New Jersey Shelf. The calculations indicate the importance of downward refracting profiles and the strength of near-interface gradients for increasing energy loss. Principal characteristics of the MACs that are observed from the calculations include: increases with interface gradient, reordering of least attenuated modes, and variations of the frequency power-law exponents of the MACs from f-1 to f1 at frequencies up to 2 kHz. Evidence of the behavior observed in the calculations is in good agreement with previous analysis of results in Gulf of Mexico experiments [F. Ingenito, J. Acoust. Soc. Am. 53, 858--863 (1973)] , for profiles that were classified as weakly downward refracting or nearly isospeed. [Work partially supported by ONR.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.2934741
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2008
    detail.hit.zdb_id: 1461063-2
    Location Call Number Limitation Availability
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    Online Resource
  • 3
    Online Resource
    Online Resource
    Dependence of modal attenuation coefficient frequency variation on upper sediment attenuation
    Acoustical Society of America (ASA) ; 2005
    In:  The Journal of the Acoustical Society of America Vol. 117, No. 4_Supplement ( 2005-04-01), p. 2496-2496
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 117, No. 4_Supplement ( 2005-04-01), p. 2496-2496
    Abstract: The range-averaged transmission loss increase in shallow water propagation depends critically on the intrinsic attenuation of the upper sediment. The attenuation coefficients of low-frequency ( & lt;1 kHz) propagating modes determine the frequency dependence. Ingenito [J. Acoust. Soc. Am. 53, 858–863 (1973)] showed with measurements and theory that while individual mode attenuation coefficients decrease with frequency f, the sediment attenuation coefficient increases proportional to f1.75. When results from many other shallow-water transmission experiments (broadband and narrowband) over sandy-silty sediments are compared to numerical calculations, it is found that a nonlinear-frequency dependent attenuation is required with an exponent between 1.5 and 2. The question considered here is how the intrinsic upper-sediment attenuation produces such behavior. A recent simplification of the Biot model [A. D. Pierce et al., J. Acoust. Soc. Am. 114, 2345 (2003)] has a power-law exponent of two. With this frequency-dependent bottom attenuation, a two-layer Pekeris waveguide yields modal attenuation coefficients that decrease with frequency as observed by Ingenito. However, a depth-dependent attenuation profile or a third near-surface layer with requisite properties can reverse this behavior. This suggests why higher-frequency numerical computations may require nonlinear frequency-dependent sediment profiles to calculate sound transmission accurately. [Work partially supported by ONR.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4787986
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2005
    detail.hit.zdb_id: 1461063-2
    Location Call Number Limitation Availability
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    Online Resource
  • 4
    Online Resource
    Online Resource
    Frequency dependence of modal attenuation coefficients from a simplified Biot sediment model
    Acoustical Society of America (ASA) ; 2004
    In:  The Journal of the Acoustical Society of America Vol. 115, No. 5_Supplement ( 2004-05-01), p. 2400-2400
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 115, No. 5_Supplement ( 2004-05-01), p. 2400-2400
    Abstract: Determination of the frequency behavior of modal attenuation coefficients is essential for estimation of propagation influences of poro-elastic sediments. A recent simplification of the Biot model [Pierce et al., J. Acoust. Soc. Am. 114, 2345 (2003)] provides an approach for this determination. For plane compressional waves in a homogeneous medium, the simplified theory reproduces the frequency-squared behavior of the full Biot model. However, data from a variety of shallow water locations suggests power-law exponents that are less than two. Inhomogeneities, particularly in the upper sediment layer, influence the frequency behavior. For a normally consolidated sediment (one never subjected to pressures higher than the current overburden pressure), depth profiles of porosity and sound speed can be estimated [Cederberg et al., J. Acoust. Soc. Am. 97, 2754–2766 (1995)] . We use these profiles to investigate the frequency behavior of the modal attenuations. Comparisons are provided with observations as well as previous numerical studies. [Work supported by ONR.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4780822
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2004
    detail.hit.zdb_id: 1461063-2
    Location Call Number Limitation Availability
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    Online Resource
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