Modeling acoustic time reversal in random shallow water sound channels

Abstract

The robust spatial and temporal focusing properties of time-reversing arrays (TRAs) are limited or lost when the environment is dynamic, acoustic absorption losses are prevalent, or noise contaminates the received signal(s). This talk presents theoretical and simulated performance results for TRAs deployed in shallow ocean sound channels containing a random linear superposition of internal waves or having a random rough bottom. In both cases, TRA retrofocusing is improved by random propagation and vertical linear TRAs are predicted to have significant azimuthal directivity. Scaling laws for this azimuthal directivity that include the signal frequency, the characteristics of the sound channel, the properties of the randomness, and the assumption of weak azimuthal coupling are presented. These scaling laws are found to successfully collapse results for a wide parametric range of N by 2-D parabolic equation simulations of TRA retrofocusing in shallow ocean sound channels with random propagation. As expected, the TRA retrofocusing improvements derived from random propagation are typically degraded and are eventually lost when the environmental randomness is time varying. However, the time scales of the oceanic fluctuations appear to be long enough to allow successful TRA operations in shallow ocean waters. [Work sponsored by ONR.]