Iterative time reversal in the ocean

The iterative time-reversal process focusing on the strongest scatterer in a multitarget medium has been described theoretically in terms of eigenvalues and eigenvectors of a time-reversal operator K*K in ultrasonics Prada et al., J. Acoust. Soc. Am. 97, 62–71 (1995). In this paper, we extend the concept of iterative time-reversal to waveguide propagation in the ocean. For a single target, the iterative time-reversal process results in a minor improvement in spatial focusing. However, data from a recent experiment in the Mediterranean Sea Kuperman et al., J. Acoust. Soc. Am. 103, 25–40 (1998) illustrates the importance of the waveguide and source transducer characteristics even in the single target case. When the ocean contains several reflectors, iterative time-reversal focuses on the target corresponding to the largest eigenvalue of the time-reversal operator, which depends not only on the reflectivity of the targets, but also on the complex propagation effects between the targets and time-reversal mirror. Analysis of the experimental data for a single target and simulation results with multiple targets in the ocean are presented.