The application of coupled-mode theory to propagation in shallow water with randomly varying sound speed
Sound propagation in the Baltic Sea cannot be described correctly by range independent propagationmodels, even for areas with more or less constant water depths. The reason is the inability of suchmodels to take account of the effect of forward scattering of sound produced by horizontal variationsin the speed of the sound. Schneider and Sellschopp have simulated the forward-scattering effect byapplying a parabolic equation method in conjunction with a Monte Carlo ray tracing program (MOCASSIN). This paper treats forward scattering in the normal mode concept, using the mode coupling formulation given by S.T. McDaniel. The mode coupling was added to the SUPERSNAP normal-mode code. Comparisons are made with the Schneider-Sellschopp calculations and with real data.