A model for four-dimensional coastal internal waves with applications to acoustics.
James F. Lynch, Timothy F. Duda, Ying-Tsong Lin, Arthur E. Newhall, and Pierre F. J. Lermusiaux

         Acousticians need a fully four-dimensional (4-D) coastal oceanography model that can provide the soundspeed field down to the internal wave scale. While mesoscale ocean models exist, given the complexities of a full primitive equation (i.e., nonlinear), non-hydrostatic, fine-scale model including internal waves, it may be a decade or more before such a model is available from the mainstream oceanographic community. We pose the possibility of creating a usable approximate 4-D ocean model based on a combination of powerful acoustics techniques, the Weinberg-Burridge vertical modes and horizontal ray solution to the wave equation, and existing primitive-equation ocean models and two-dimensional nonlinear wave equations. In our technique, the local ocean internal wave modes are found, creating a horizontal index of refraction grid for internal-tide ray tracing from identified source points. Broadband internal waves are propagated along the trajectories using the KdV or other appropriate nonlinear wave equation, with internal-tide initialization and interpolation between trajectories. An ocean numerical model with good bathymetry provides the source distribution as well as bouancy frequency profiles and current profiles, necessary inputs for the internal wave modes and propagation. The initial design for this model as well as examples of its usages for ocean acoustics are presented.

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