Scaling of time-reversing array performance in the presence of ambient noise

Abstract

Time-reversing arrays (TRA) have the capability to exploit unknown multipath environments to retrofocus acoustic waves, in both time and space, back to their original source location. Although TRA retrofocusing may be robust, it is degraded by ambient noise. The noise received by the array and the noise existing locally in the focal region cause a reduction in the focal-point signal-to-noise ratio and simultaneous waste of the useful power output of the array. A vertical TRA operating in simple environments containing an isotropic noise field is considered. A focal probability criteria is developed to quantify the retrofocusing performance of the TRA. This approach leads to a simple scaling law that incorporates the ambient noise level, the original source level, the array element level, the array element number, and the acoustic environment parameters. Results for free space and a shallow-water sound channel will be presented. Operating regimes strongly influenced by original source level and TRA element power level are clearly defined by this effort. [Work sponsored by the Office of Naval Research, Ocean Acoustics.]