This paper presents a detailed analysis of the effects of noise (reverberation) on the focusing performance of de-composition of the time reversal operator (DORT) in a noise-limited case and in a reverberation-limited case, respectively. Quantitative results obtained from simulations and experiments are presented. The results show the DORT method can be effi-ciently applied to target detection with enough source level to yield significant backscatter. For a target placed on the bottom, the influence of the reverberation on the focusing performance is slight. However, distinguishing between a target and constant backscattering returning from strong local clutter on the bottom (false alarms) needs further research.
With the spatial-temporal focusing of acoustic energy,time reversal processing(TRP) shows the potential application for active target detection in shallow water.To turn the ‘potential’ into a reality,the TRP based on a model source(MS) instead of a physical probe source(PS) is investigated.For uncertain ocean environments,the robustness of TRP is discussed for the narrowband and broadband signal respectively.The channel transfer function matrix is first constructed in the acoustic perturbation space.Then a steering vector for time reversal transmission is obtained by singular value decomposition(SVD) of the matrix.For verification of the robust TRP,the tank experiments of time reversal transmission focusing and its application for active target detection are undertaken.The experimental results have shown that the robust TRP can effectively detect and locate a small bottom target.
