Review of numerical models in underwater acoustics including recently developed fast-field program

Abstract

Two papers given by SACLANTCEN personnel at the NATO Advanced Research Workshop on Hybrid Formulation of Wave Propagation and Scattering at Castel Gandolfo, Rome, Italy on 30 August to 3 September 1983 are published as a review of SACLANTCEN's recent programme in underwater-acoustic modelling. The first briefly reviews the physics of sound propagation in the ocean. In it the mathematical foundations of the most widely used acoustic models (ray, mode, fast field, parabolic equation) are presented and the areas of applicability of the various models are indicated. A few numerical examples are included to show the consistency among the different computer models in overlapping regimes of validity. A series of computational examples is given to demonstrate the applicability of these models to a wide range of general wave-propagation problems. The second paper presents a new numerical model, of the fast field type, where the depth-separated wave equation is solved by a numerical technique very similar to that used in finite-element programs. The speed improvement over existing models of the same type is considerable, especially in cases with many sources and receivers. The model has been used for studying both seismic pulse propagation in shallow water and reflection of pulsed ultrasonic beams from a fluid/solid interface.