Echo to reverberation enhancement with time-reversal methods in the ocean

Abstract

Reverberation from a rough ocean boundary often degrades the performance of active systems in shallow water. In this study, two time-reversal methods are investigated to enhance the echo-to-reverberation ratio by focusing more acoustic energy in the water column rather than on the ocean boundary. The first method is with a probe source in the middle of the water column. A time-reversal process with the probe signal realizes a focus at the probe signal position and shadows the boundaries below and above the focus resulting in reduced reverberation and increased target echo. The second method is without a probe source. An eigen-decomposition of the reverberation signal provides the transfer function information between the source and the scatterers where the reverberation is generated. The backprogation from a source array weighted by nondominant eigenvectors minimize the acoustic field incident on the corresponding boundary. Both of these methods place a notch in the returning reverberation signal. The results from numerical simulations as well as an ocean experiment will be discussed. [Work supported by ONR.]