The ray-tracing code BELLHOP was used to determine the transfer function between a sound source and a field point.  The transfer function in the frequency domain obtained from BELLHOP was transformed into the time domain. 
BELLHOP
Underwater Sound Source Localization Based on Passive Time-Reversal Mirror and Ray Theory.This study investigates the performance of a passive time-reversal mirror (TRM) combined with acoustic ray theory in localizing underwater sound sources with high frequencies (3-7 kHz).  The TRM was installed on a floating buoy and comprised four hydrophones.  The pressure field was then obtained by taking the convolution of the transfer function in the time domain with the time-reversed signals that were received by the hydrophones in the TRM.  The aforementioned tests revealed that even when the distances between a source and the TRM were up to 1600 m, the distance deviations between estimated and actual source locations were mostly less than 2 m.  Errors originated mainly from inaccurate depth estimation, and the literature indicates that they can be reduced by increasing the number of TRM elements and their apertures.
TRM