Effects of an Undulating Bottom on the Propagation of Sound in Shallow Water

Abstract

Experiments are described that show that the transmission loss over various paths in shallow water is highly variable. Known factors that influence the transmission loss are the temperature profile, the bottom type, the water depth, and fish. In this paper, we consider the effect of an undulating bottom. A computer simulation of shallow water sound propagation—using ray theory, empirical bottom reflection coefficients, and random phase shifts to represent the effect of the undulating bottom—indicates that there should be several decibels' variation in the transmission losses over equidistant paths differing slightly in bearing. The rms variation in transmission loss is predicted to increase with range and frequency and decrease with increasing bottom loss. The undulating bottom reduces the “quality” of the waveguide consisting of the surface and bottom and thereby reduces mode structure and reduces the transmission loss caused by phase effects.