Time reversal experiments in the ocean

A time-reversal mirror (TRM) (or phase conjugate array) spatially and temporally refocuses an incident acoustic field back to its origin. Bill Kuperman and colleagues at the Marine Physical Laboratory of the Scripps Institution of Oceanography carried out a series of time reversal experiments 1996–2006 in collaboration with Tuncay Akal and colleagues at the NATO SACLANT Undersea Research Centre (now Center for Maritime Research and Experimentation) in La Spezia, Italy. The initial experiments were carried out in shallow water off the west coast of Italy. These utilized a 77 m aperture source-receiver array (SRA) along with a probe source deployed by the R/V Alliance and a 90 m aperture receive array for exploring the focal region from the SRA transmissions. These experiments demonstrated TRM focusing at ranges 5–30 km, explored temporal stability of the focus (hours to days), demonstrated moving the focus + /−10% range through shifting the center frequency of the received pulse, and impact of implementing an iterative time reversal process. In subsequent experiments, the SRA was redesigned to operate at high frequency (3.5 kHz) enabling exploring time reversal applications in acoustic communications and reverberation nulling. The presentation will show highlights from this series of time reversal experiments.