Time reversal matched field

Abstract

Time reversal techniques obtain increased resolution by exploiting scattering and multipath in propagation through inhomogeneous channels. Fink and collaborators has used time reversal to achieve super-resolution focusing in acoustics with controlled ultrasonic experiments in water tanks. More recently large-scale acoustics experiments in the ocean have confirmed the resolution ability of time reversal. In this paper, matched field detection with time reversal (TR-MFP) is considered. In classical matched field processing (MFP), detailed modeling of the channel is used to predict the field as received by an array of sensors, after the wavefield propagates through an inhomogenous channel. MFP, in simple terms, solves an inverse problem (source detection or location) by stepping through a sequence of forward problems, where in each forward problem the unknown location of the source is postulated at each one of potential positions. Practical implementation of MFP implies the solution of the wave equation for each forward problem assuming a given channel velocity propagation profile and given boundary conditions. Time reversal provides a very good alternative to MFP, and provides the potential gain from matching to the propagated field, rather than matching to the original transmitted wavefield. The actual channel Greens' function, in contrast with MFP where the channel Greens' function is computed from the model.