The effect of range dependence on acoustic propagation in a convergence zone environment

Abstract

The effect of a range-dependent environment, typified by fronts or eddies, or convergence zone intensities is investigated. An analytical approach is taken to examine vertical redistribution of acoustic energy resulting from explicit changes in sound channel structure and from implicit effects of horizontal sound-speed gradients. Under certain oceanographic conditions, such a redistribution is shown to lead to catastrophic signal losses at all ranges for receivers at fixed depths. A generalized Snell’s law in a range-dependent environment is derived and then utilized to identify regions where such losses may occur. It is shown that large changes in transmission result only when horizontal sound-speed changes evaluated over a ray path are not small compared with the amount of sound-speed depth excess. Several examples are presented illustrating the theory using parabolic equation numerical simulations. A method is also presented to predict expected signal losses as a function of source position in an eddy or front.