The Effects of Horizontally Varying Internal Wave Fields on Multi-Path Interference of Refracted-Refracted Propagation about the Deep Sound Channel Axis

Abstract

Fluctuations of CW signals transmitted through real ocean paths are characterized by smooth slow variations in phase and rapid noise-like variations in amplitude. These variations are the result of internal waves, which perturb the sound-speed field and thereby produce time-varying multi-path interference. This study is concerned with modeling the effects of horizontal and vertical variations in the sound-speed field on multi-path interference of CW propagation for the particular case of refracted-refracted ray paths. The vertical sound-speed profile is approximated by two layers of linear gradient and arbitrary horizontal variations are introduced by numerical methods. The travel times along individual ray paths are influenced by fluctuations of the internal wave fields with horizontal scales which are (1) approximately equal to the cycle distance of the ray paths or (2) greater than several cycle distances of the ray. Both types of disturbances induce multi-path interference but the later also produces phase shifts for all ray paths. The model approximates fixed-system experiments on CW propagation between Eleuthera and Bermuda. We show that horizontally invariant internal tide cannot cause both phase and amplitude statistics which are consistant with experiment.