Ocean acoustic models for low frequency propagation in 2D and 3D environments

In this paper we are mainly concerned with the development of efficient com puter models capable of accurately predicting the propagation of low-to-mid dle frequency sound in the sea, in axially symmetric (2D) and in fully 3D e nvironments. The major physical features of the problem, i.e. a variable bo ttom topography, elastic properties of the subbottom structure, volume atte nuation and other range inhomogeneities are efficiently treated. The comput er models presented are based on normal mode solutions of the Helmholtz equ ation on the one hand, and on various types of numerical schemes for parabo lic approximations of the Helmholtz equation on the other. A new coupled mo de code is introduced to model sound propagation in range-dependent ocean e nvironments with variable bottom topography, where the effects of an elasti c bottom, of volume attenuation, surface and bottom roughness are taken int o account. New computer models based on finite difference and finite elemen t techniques fur the numerical solution of parabolic approximations are als o presented. They include an efficient modeling of the bottom influence via impedance boundary conditions, they cover wide angle propagation, elastic bottom effects, variable bottom topography and reverberation effects. All t he models are validated on several benchmark problems and versus experiment al data. Results thus obtained were compared with analogous results from st andard codes in the literature.