Experimental investigation of bottom target detection by single channel iterative time reversal

Abstract

Iterative time reversal process will gradually lead echo waves to converge to a dominant narrowband resonant mode of the target and enhance the return level in noisy and reverberant environment. This technique is used in bottom target detection and an experiment has been performed in the Yellow Sea, China. The experiment is in a monostatic configuration, and the target, which is a 53 cm external diameter and 260 cm long stainless steel cylindrical shell with concrete in interior, is resting on the sea floor, and the directional transceiver, which is a transmitter and receiver couple, is located right above the target. Firstly, a broadband interrogation pulse is launched, and the echo is measured and a bandpass filter is applied to avoid transceiver response peak, then the signal is time reversed and retransmitted, and repeat above procedures iteratively. The bottom reverberation will gradually be suppressed, and the center frequency of converged signal corresponds to a target resonance mode, which is different from inhomogeneous bottom response in no target case. The existence of target is determined by this important acoustic signature, and the results illustrate the feasibility of this method.