Robust time-reversal is combined with distributed multiple-input multiple-output sonar for detection of small targets in shallow water environments

The distributed multiple-input multiple-output (MIMO) system exploits the spatial diversity for enhancement of target detection. Time reversal processing (TRP) is based on the acoustic reciprocity to enhance target echoes and suppress reverberation. This paper presents an attempt of combining TRP with the distributed MIMO processing for detection of small targets in shallow water environments. For improvement of robustness of the distributed TR-MIMO sonar system, we consider the iterative time reversal mechanism in the processing framework. A probing signal is firstly transmitted to sense the environment and observe echoes of the likely targets. Then, the target of interest is simultaneously illuminated from different angles by time-reversal beams in the second transmission. With a broadband spatial-temporal model, we analyze the time-reversal gain in the distributed MIMO processing and design a MIMO detector in the Neyman-Pearson sense. Results of numerical simulation have shown that the distributed TR-MIMO sonar system outperforms the TR sonar system in the high SNR regime. Due to benefits of robust time-reversal focusing, the distributed TR-MIMO sonar system performs well in localization of a small target in at-lake experiments.