Resolution Estimation for Imaging and Time Reversal in Scattering Media

An array of transducers receives the signals emitted by a localized source in a scattering acoustic medium. The recorded signals can be used either in a time-reversal (TR) process in order to refocus acoustic energy back onto the source, or in a matched field imaging (MF) process in order to estimate the source location. In TR the signals are time-reversed and emitted into the physical medium whereas in MF they are time-reversed and back-propagated numerically in a fictitious homogeneous medium. Given the range (distance from the array) of the active source we study here the cross-range resolution in these two processes. As expected, multiple-scattering enhances the refocusing resolution in TR but it degrades resolution in the estimation of the source location with MF. We introduce a robust procedure for estimating the resolution gain (resp. loss) in TR (resp. MF), in weakly scattering random media. Direct numerical simulations in the ultrasound regime show that our estimation method is accurate and effective.