Effects of ocean turbulence on multipath beamforming

Abstract

In this report, effects of ocean environments on a sonar array pattern is evaluated by a theoretical approach, the path integral technique, and a numerical simulation method, the split-step method. The contributions of turbulence and deterministic sound-speed distribution in the ocean are considered. The former contribution broadens the synthesized beamwidth and the latter one interferes with the array pattern through the existence of multipath. It is found that turbulence can also smooth the pattern interference. Both the cases of temperature fine structures and a Gaussian spectrum are used to model the fluctuation of the sound-speed distribution. The result shows that the former model has stronger smoothing effect when they have the same fluctuation strength. In the numerical simulation, the average array pattern is shown to be similar to the theoretical one. It is illustrated that both the normalized beamwidth and its variance of the array pattern are increased as sound-speed fluctuation strength increases or the scale length of turbulence decreases.