Detection and localization of a target in shallow water between two source-receive ultrasonic arrays: A small-scale experiment demonstration.

Abstract

We experimentally demonstrate the detection and localization of a wavelength‐size target in a shallow ultrasonic waveguide between two source‐receive arrays. The waveguide represents a 1.5‐km‐long, 50‐m‐deep ocean acoustic channel at the 1/1000 scale, in which two coplanar arrays would record the broadband transfer matrix around 3 kHz. Invoking reciprocity principle, we perform a time‐domain double beamforming algorithm simultaneously on the source and receive array. This array processing projects the multi‐reverberated acoustic signals recorded between each source and each receiver into an equivalent set of eigenrays defined by their launch and receive angles. Comparison is made between the intensity of each eigenray with and without the target in the ultrasonic waveguide. When detection is achieved, localization is performed through the back projection of each eigenray into the acoustic waveguide weighted by the intensity fluctuation induced by the target. The use of the diffraction‐based sensitivity kernel for each eigenray improves the localization of the target. Detection and localization experimental results will be shown in the presence of surface waves for ultrasonic arrays at 1 and 3 MHz.