Effects of time-reversing array deformation in an ocean waveguide

Abstract

Active acoustic time reversal is a technique for transmitting and focusing sounds recorded in complex unknown environments back to their remote point(s) of origin. It can be accomplished with a transducer array—a time-reversing array (TRA) or time-reversal mirror (TRM) that can both send and receive sound. Nearly all prior work on underwater TRA performance has involved stationary arrays. This presentation describes how random array deformation influences TRA retrofocusing in a shallow ocean environment. Both theory and simulation results are presented for frequencies of 250, 500, and 750 Hz. For harmonic signals, randomly drifting array elements degrade TRA performance by approximately 20% when the average horizontal wave number times the root-mean-square horizontal element displacement approaches one half. For randomly rising or sinking elements, TRA performance is similarly degraded when the average vertical wave number times the root-mean-square vertical displacement reaches four or five. [Work supported by ONR.]