The Effects of Horizontally Varying Internal Wave Fields on Multipath Interference for Propagation through the Deep Sound Channel

Fluctuations of CW signals transmitted through real ocean paths are characterized by smooth slow variations in phase and rapid noise-like variations in transmission loss. The variations are thought to be the results of internal waves, which perturb the sound speed field and thereby produce time-varying multipath interference. This study is concerned with modeling the effects of large-scale horizontal and vertical perturbation of the sound speed field on multi-path interference of CW transmission, for the particular case of long-range propagation through the deep sound channel. The vertical profile is approximated by two layers of linear sound speed gradient and arbitrary horizontal variations are introduced by numerical methods. Propagation is modeled for internal wave field which is invariant, coherent, or random in the horizontal. The travel times along individual ray paths are shown to be influenced by fluctuations of the internal wave field with horizontal scales which are (1) approximately equal to the cycle distance of the ray or (2) greater than several cycle distances of the ray. Both scales of disturbance induced multipath interference but the latter also induces temporally correlated phase shifts for all rays.