Acoustic characterization of the seabed with a single-element time-reversal mirror

Motivated by the 2012 Florida Straits Noise Interferometry Experiment, this paper investigates a time-reversal-based approach to acoustic remote sensing of the ocean. The signal processing mimics operation of a physical time-reversal mirror. The input data for the simulated time-reversal mirror can be obtained using either a compact, broadband sound source or cross-correlation of the diffuse noise recorded by spatially separated receivers. Low-frequency sound propagation is considered over ranges that are large compared to the water depth. The approach exploits the notion that the “best” focusing of the backpropagated time-reversed signal occurs at the “right point,” when the backpropagation takes place in the same propagation medium as the one, where the data have been acquired. Various metrics of the focusing quality are considered. A combination of spatial and temporal characteristics of the focus is proposed that leads to a robust and unique solution of the geoacoustic inverse problems considered for a single-element passive time-reversal mirror. Inputs with rather low signal-to-noise ratio prove acceptable, which is particularly important in the passive remote sensing context.