Inversion of ocean environmental variations via time-reversal acoustics

Abstract

Time-reversal (TR) processing is derived from the invariance of the wave equation for a lossless medium to change of the sign of the time variable. By retransmitting the TR version of the time-dispersed received signal propagated from a probe source (PS) to a source-receiver array (SRA), one can reacquire the probing pulse at the PS location (time compression and spatial focusing) when the waveguide environment is time invariant. However, if some environmental variations occur between the two transmissions, the retrofocusing signal will be defocused. This paper presents an inversion method of ocean environmental variations, which exploits the focusing/defocusing effect measured at the PS location in the presence of environmental perturbations between the PS transmission and the SRA retransmission. Specifically, inversion of the sound speed profile represented in terms of the empirical orthogonal functions is developed. Examples of the method applied to synthetic data are provided to demonstrate the method's feasibility.