• Login
    About WHOAS
    View Item 
    •   WHOAS Home
    • Woods Hole Oceanographic Institution
    • Academic Programs
    • WHOI Theses
    • View Item
    •   WHOAS Home
    • Woods Hole Oceanographic Institution
    • Academic Programs
    • WHOI Theses
    • View Item
    JavaScript is disabled for your browser. Some features of this site may not work without it.

    Browse

    All of WHOASCommunities & CollectionsBy Issue DateAuthorsTitlesKeywordsThis CollectionBy Issue DateAuthorsTitlesKeywords

    My Account

    LoginRegister

    Statistics

    View Usage Statistics

    Analysis of modal evolution caused by a weakly range-dependent seabed in shallow water and its application to inversion for geoacoustic properties

    Thumbnail
    View/Open
    Ohta_thesis.pdf (38.89Mb)
    Date
    1993-09
    Author
    Ohta, Kazuhiko  Concept link
    Metadata
    Show full item record
    Citable URI
    https://hdl.handle.net/1912/5510
    Location
    Nantucket Sound
    Hudson Canyon
    DOI
    10.1575/1912/5510
    Keyword
     Marine sediments; Ocean bottom; Sound 
    Abstract
    In a shallow water ocean environment, the range-dependent variation of the geoacoustic properties of the seabed is one of the crucial factors affecting sound propagation. Since the local modes of propagation depend on the spatial changes in the bottom sediments, the local eigenvalues of these modes are useful as tools for examining the range dependence of the sediment properties. In order to extract the local eigenvalues from measurements of the pressure field in a laterally inhomogeneous waveguide, the zero-order asymptotic Hankel transform with a short sliding window is utilized. The local peak positions in the output spectra differ from the local eigenvalues due to both the range variation of the local modes and the interference of adjacent modes. The departure due to the former factor is evaluated analytically by using the stationary phase method. In order to reduce the error induced by the latter factor, mode filtering is utilized by incorporating data from a fixed vertical array of receivers. The use of the above zero-order Hankel transform in a three-dimensionally varying waveguide results in an underestimate of the local eigenvalues due to the effect of horizontal refraction. Thus a general asymptotic Hankel transform with a 2-D sliding window is used to correct for the underestimated amount. By expanding the latter transform with respect to the azimuthal angle, it can also be shown that the first term in the Taylor series corresponds to the former transform; the rest of the terms account for the value difference between the underestimated and actual local eigenvalues. In order to obtain the spatial variation of the sediment properties from the rangedependent variation of the extracted local eigenvalues, the analytical relationship between these two variations is derived by using a perturbation method in a horizontally varying, multi-layered bottom model. Upon use of the n2-linear profile in each layer, the relationship can be obtained in closed form. As a result, the range variation of the local eigenvalues may be separated into terms that depend on each geoacoustic parameter. Based on this relation, an inversion method for determining the range-dependent geoacoustic parameters is developed. The methods developed in this thesis are applied to simulated pressure field data as well as experimental field data. It is shown that the evolution with range of the local modes as well as the range-dependent geoacoustic properties can be successfully estimated.
    Description
    Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1993
    Collections
    • WHOI Theses
    • Applied Ocean Physics and Engineering (AOP&E)
    Suggested Citation
    Thesis: Ohta, Kazuhiko, "Analysis of modal evolution caused by a weakly range-dependent seabed in shallow water and its application to inversion for geoacoustic properties", 1993-09, DOI:10.1575/1912/5510, https://hdl.handle.net/1912/5510
     

    Related items

    Showing items related by title, author, creator and subject.

    • Thumbnail

      Ciliate micrograzer dynamics of the New England Shelf 

      Brownlee, Emily F. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2017-06)
      Protists play important roles in grazing and nutrient recycling, but quantifying these roles has been hindered by difficulties in collecting, culturing, and observing these often-delicate cells. During long-term deployments ...
    • Thumbnail

      Enabling human-robot cooperation in scientific exploration of bandwidth-limited environments 

      Jamieson, Stewart Christopher (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2020-05)
      Contemporary scientific exploration most often takes place in highly remote and dangerous environments, such as in the deep sea and on other planets. These environments are very hostile to humans, which makes robotic ...
    • Thumbnail

      Measurements and dynamics of multiple scale bedforms in tidally energetic environments 

      Jones, Katie R. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2018-06)
      The presence of superimposed bedforms, where smaller bedforms exist on larger bedforms, is ubiquitous to energetic tidal environments. Due to their wide range in scale, it is difficult to simultaneously observe these ...
    All Items in WHOAS are protected by original copyright, with all rights reserved, unless otherwise indicated. WHOAS also supports the use of the Creative Commons licenses for original content.
    A service of the MBLWHOI Library | About WHOAS
    Contact Us | Send Feedback | Privacy Policy
    Core Trust Logo