Identification of a resonant target buried in sediment using iterative, single channel, time reversal

Abstract

The presence of noise and clutter makes identification of targets buried beneath the seafloor a challenging problem. Iterative time reversal using a single-channel transducer is shown to enhance the signal-to-noise ratio of backscattered echo returns from a buried resonant target. Each iteration consists of: (1) Insonifying the target with a broadband pulse, (2) windowing a portion of the backscattered echo return, (3) reversing it in time, and (4) using this waveform as the source signal for the subsequent interrogation. Scaled laboratory experiments are performed with a broadband (rmQ∼2) transducer, operating between 500 kHz and 2 MHz, and a 6.35 mm diam hollow aluminum spherical shell target buried beneath a layer of simulated sediment. When the target is located within the time reversal window, there is a rapid convergence to a narrowband signal characteristic of a dominant mode of the target’s scattering response. Images are generated by scanning the transducer laterally in two dimensions above the buried target. The images reveal enhancement of different resonant modes of the target, depending on the transducer’s position. Results will also be reported from larger-scale experiments performed in a test pond at lower frequencies. [Work supported by Office of Naval Research Award No. N000140610044.]