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  • Acoustic scattering  (2)
  • Cross sections  (2)
  • 1
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    Sound scattering by spherical and elongated shelled bodies (2008)
    Acoustical Society of America
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Acoustical Society of America, 1990. 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 88 (1990): 1619-1633, doi:10.1121/1.400321.
    Description: Describing the scattering of sound by elongated objects with high aspect ratios (ratio of length to diameter) usually involves great numerical difficulties. The recently developed deformed cylinder solution was shown to be increasingly accurate in the limit of very high aspect ratios (≥5:1) while requiring relatively low computation times and was applied to objects of constant composition [T. K. Stanton, ``Sound scattering by cylinders of finite length. III. Deformed cylinders,'' J. Acoust. Soc. Am. 86, 691–705 (1989)]. In this article, the approximate formulation is used to describe scattering by prolate spheroids, straight finite cylinders, and uniformly bent cylinders where the objects are composed of an elastic shell surrounded by fluid and filled with either a fluid or gas. The calculations are compared with those involving spherical shells based on the formulation derived in Goodman and Stern [J. Acoust. Soc. Am. 34, 338–344 (1962)]. The calculations are made over a wide range of frequencies and shell thicknesses (ranging from solid elastic objects to thin-shelled objects). Since the deformed cylinder formulation is most accurate for angles of incidence normal or near normal to the lengthwise axis, the calculations are limited to broadside incidence. The simulations show significant variations in the modal interference structure as the shell thickness and shape are varied. Comparisons are also made between predictions and laboratory data involving straight and bent finite-length cylindrical shells (stainless steel) with 3:1 aspect ratios and 52% shell thicknesses. The study not only shows reasonable agreement between the predictions and data, but also illustrates the dramatic change in scattering cross section due to the bend of the object (12 dB in this case).
    Description: This work was supported in part by the U.S. Office of Naval Research
    Keywords: Scattering ; Sound waves ; Shells ; Cylindrical configuration ; Spherical configuration ; Cross sections
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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    New broadband methods for resonance classification and high-resolution imagery of fish with swimbladders using a modified commercial broadband echosounder (2010)
    Oxford University Press
    Details
    Publication Date: 2022-05-25
    Description: © 2010 The Authors. This article is distributed under the terms of the Creative Commons Attribution-Noncommercial License. The definitive version was published in ICES Journal of Marine Science: Journal du Conseil 67 (2010): 365-378, doi:10.1093/icesjms/fsp262.
    Description: A commercial acoustic system, originally designed for seafloor applications, has been adapted for studying fish with swimbladders. The towed system contains broadband acoustic channels collectively spanning the frequency range 1.7–100 kHz, with some gaps. Using a pulse-compression technique, the range resolution of the echoes is ~20 and 3 cm in the lower and upper ranges of the frequencies, respectively, allowing high-resolution imaging of patches and resolving fish near the seafloor. Measuring the swimbladder resonance at the lower frequencies eliminates major ambiguities normally associated with the interpretation of fish echo data: (i) the resonance frequency can be used to estimate the volume of the swimbladder (inferring the size of fish), and (ii) signals at the lower frequencies do not depend strongly on the orientation of the fish. At-sea studies of Atlantic herring demonstrate the potential for routine measurements of fish size and density, with significant improvements in accuracy over traditional high-frequency narrowband echosounders. The system also detected patches of scatterers, presumably zooplankton, at the higher frequencies. New techniques for quantitative use of broadband systems are presented, including broadband calibration and relating target strength and volume-scattering strength to quantities associated with broadband signal processing.
    Description: The research was supported by the US Office of Naval Research, grants number N00014-04-1-0440 and N00014-04-1-0475, NOAA/CICOR cooperative agreement NA17RJ1223, NOAA/ National Marine Fisheries Service, and the J. Seward Johnson Chair of the WHOI Academic Programs Office.
    Keywords: Acoustic scattering ; Broadband ; Echosounder ; Fish ; Resonance
    Repository Name: Woods Hole Open Access Server
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  • 3
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    Sound scattering by live zooplankton and micronekton : empirical studies with a dual-beam acoustical system (2008)
    Acoustical Society of America
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Acoustical Society of America, 1990. 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 88 (1990): 2346-2360, doi:10.1121/1.400077.
    Description: Measurements and analyses are presented of the backscattering of 420-kHz sound by 43 individual animals of representative zooplanktonic and micronektonic taxa. Direct measurements of an individual's target strength were made with a commercial dual-beam sonar system in an enclosure filled with filtered seawater deployed off a dock at Friday Harbor, Washington. The dependence of target stengths upon individual length, wet weight, and dry weight was investigated. In addition, the ``target strength'' and statistical variations of echo amplitude due to variations in shape and orientation of the organism were compared with acoustic scattering models involving different shapes (the general shapes of the sphere, and straight and uniformly bent finite cylinders were used along with attempts to take into account roughness). It was found that: (1) backscattering cross sections are proportional to volume of the organisms rather than area as would be predicted by a sphere scattering model, (2) mean target strength based on average backscattering crossection is best described by the bent cylinder model whose modal series solution is truncated, and (3) the fluctuations of the echo amplitudes are well described by the Rice probability density function whose shape parameter is related to the randomly rough straight cylinder model. These extensive studies showed conclusively that the elongated animals scattered sound more like elongated targets than spherical ones, thus demonstrating the need for models more sophisticated than the spherical ones routinely used to date. The data and model analyses provide a basis for devising future acoustical data acquisition and processing techniques for bioacoustical field studies.
    Description: This research was supported by the Oceanic Biology and Ocean Acoustics Programs of the Office of Naval Research Contract Nos. N00014-87-K-007 and N00014-89-J-1729, respectively and the National Science Foundation Grant No. OCE-8709962.
    Keywords: Sound waves ; Backscattering ; Khz range 100–1000 ; Zooplankton ; Cross sections ; Sonar ; Remote sensing
    Repository Name: Woods Hole Open Access Server
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  • 4
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    Non-Rayleigh acoustic scattering characteristics of individual fish and zooplankton (2006)
    IEEE
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © IEEE, 2004. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 29 (2004): 260-268, doi:10.1109/JOE.2004.828208.
    Description: It has long been known that the statistical properties of acoustic echoes from individual fish can have non-Rayleigh characteristics. The statistical properties of echoes from zooplankton are generally less understood. In this study, echoes from individual fish and zooplankton from a series of laboratory measurements from the past decade are investigated. In the experiments, acoustic echoes from various individual organisms were measured over a wide range of frequencies and orientations, typically in 1/spl deg/-3/spl deg/ increments. In the analysis in this paper, the echoes from most of those measurements are grouped according to ranges of orientation, which correspond to typical orientation distributions of these organisms in the natural ocean environment. This grouping provides a distribution of echo values for each range of orientation. This approach, in essence, emulates a field experiment whereby distributions of echoes would be recorded for different distributions of orientations of the organisms. For both the fish and zooplankton data, there are conditions under which the echoes are strongly non-Rayleigh distributed. In some cases, the distribution is quantitatively connected to the physics of the scattering process while, in other cases, the connection is described qualitatively. Exploitation of the animal-specific statistics for classification purposes is suggested.
    Keywords: Acoustic scattering ; Echo statistics ; Fish ; Zooplankton
    Repository Name: Woods Hole Open Access Server
    Type: Article
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