Forward coupled-mode propagation modeling for coastal acoustic tomography

A coupled normal-mode approach for the prediction of pulse propagation in a complex coastal environment is presented. In this broadband approach, the received time-domain sound-pressure signal is generated by Fourier synthesis using the product of the source signal spectrum and the source-to-receiver ocean transfer function. For a given frequency, the basic formulation involves decomposing the acoustic pressure into slowly varying complex envelopes that modulate (mode by mode) analytic, rapidly varying, adiabatic-mode solutions. A coupled set of differential equations governing these complex modal envelopes is derived and the numerical solution techniques used are discussed. This coupled-mode approach has been used to model the modal arrival structure in the 1992 Barents Sea Coastal Acoustic Tomography Test. Model results and comparison to the data measured by a vertical hydrophone array are discussed. (C) 1996 Acoustical Society of America.