Experimental demonstration of iterative time-reversed reverberation focusing in a rough waveguide. Application to target detection

For most shallow water waveguides, the backscattered energy measured in a monostatic configuration is dominated by ocean bottom reverberation. A selected time-gated portion of the measured reverberation signal is used to provide a transfer function between a time-reversal array and a corresponding range interval on the bottom. Ultrasonic and at-sea experiments demonstrate the focusing capabilities of a time-reversal array along the rough bottom interface using these reverberation signals only. The iterative time-reversal technique facilitates robust focusing along the ocean bottom, with little signal processing effort involved and a priori information of the environment. This allows for enhanced detection and localization of proud or buried targets in complex shallow water environments. A passive implementation of the iterative time-reversal processing is used to construct reflectivity maps, similar to a sonar map, but with an enhanced contrast for the strongest reflectors (or scatterers), at the water-bottom interface. Ultrasonic and at-sea experiments show that targets on the seafloor located up to 400 wavelengths from a time-reversal array are detectable in the presence of bottom reverberation. (c) 2006 Acoustical Society of America.