2023_programme: Coupled-mode field computations for underwater canyons and ridges

• Session: 07. Modeling techniques for underwater acoustic scattering and propagation (including 3D effects)
  Organiser(s): Boris Katsnelson and Pavel S. Petrov
• Lecture: Coupled-mode field computations for underwater canyons and ridges [invited]
  Paper ID: 1912
  Author(s): Ivansson Sven
  Presenter: Ivansson Sven
  Abstract: Coupled-mode methods have been used in underwater acoustics to compute 3D sound propagation and scattering. Significant computational simplifications are possible for media with lateral variation restricted to cylindrical symmetry, and also for media which are invariant in one of the horizontal directions. The present paper explores the similarities between these two cases. For discrete coupled-modes with a reflection- (or scattering-) matrix formulation for modes, the equations for the latter case are derived as limits of the equations for the former case when the symmetry axis of the medium tends to infinity. This derivation directly provides suitable basis functions to inherit reflection-matrix symmetry, and it emphasizes the usefulness of proposed Bessel/Hankel-function scalings. The paper also includes mathematically exact field decompositions with partial waves having a natural physical interpretation. Such decompositions should be of interest for analysis of continuous-wave and broad-band results, as a complement to approximate ray methods. Reverberation operators for selected parts of the medium are expanded in terms of elementary reflection/transmission matrices for the modes. The implementation is surprisingly convenient, using reflection-matrix recursions involving selected restarts with vanishing reflection matrices. Examples for underwater canyons and ridges are given, including comparisons to previous approximate parabolic-equation results.
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• Corresponding author: Dr Sven Ivansson
  Affiliation: -2146826259
  Country: Sweden
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