Time-Reversal Mirror-Virtual Source Array Method for Acoustic Imaging of Proud and Buried Targets

This paper addresses the problem of proud and buried targets detection and localization without the need of a probe source (PS) at the target's location or the need of accurate environmental knowledge. There are three novel features in this paper. First, although the combination of time-reversal mirror (TRM) and virtual source array (VSA) method has been applied to remote imaging in previous literature, this paper further analyzes the mode leakage effect which causes the failure of some VSA implementations. Based on the analytical result, the effective deploying region for the VSA is derived. Second, to coherently focus on a buried target, the effect of sound refraction through the boundary of the water and sediment layers must be considered. The sound speeds of water and sediment layers are taken into account to correct the time-delay steering of the VSA. Since time-reversal processing (TRP) with a PS at the target location provides the best performance bound (TRB), we can quantitatively evaluate the performance improvement of our proposed modified TRM-VSA method in comparison with the conventional one according to their relationship with the TRB. This paper demonstrates that the performance of the TRM-VSA method with or without the knowledge of refraction at the boundary of different layers can differ significantly. Third, after we have successfully achieved active focusing on proud and buried targets with the modified TRM-VSA method, model-based algorithms such as matched-field processing (MFP) can extract array steering vectors from the active focusing method and achieve the task of target detection and localization. Results of simulations and tank experiments are presented as demonstrations of the three novel features of this paper.