Refracted, Bottom-Reflected Ray Propagation in a Shallow-Water Channel with Slowly Time-Varying Stratification

Abstract

The shallow-water regions of the ocean are subject to low-frequency fluctuations in stratification spacially coherent over long distances. Internal tides, which are now considered a permanent feature of many coastal areas, are an example. The present study is a preliminary investigation of the influence of these fluctuations on RBR (Refracted, Bottom-Reflected) ray propagation in a shallow water channel. The principal assumptions are that the spatial scale of the stratification fluctuations in the channel is long compared to the distance between source and receiver, and that the fluctuation time scale is long compared to the ray travel time. In addition to general relationships, a particular case with realistic channel parameters in terms of continental shelf conditions is discussed in detail. In the detailed study, it is shown that both the amplitude and phase angle of a CW signal associated with any given ray are modulated at the fluctuation frequency of the channel stratification. The amplitude modulation, however, is negligibly small so that the resultant multipath signal at the receiver is a sum of several signals nearby, constant in amplitude but phase-angle modulated.