Target detection in a shallow water environment using a two‐dimensional array.

The detection and tracking of targets in cluttered, shallow water locations have become increasingly important for both maritime security and coastal environmental monitoring. Ambient noise contributions from snapping shrimp, as well as recreational and commercial ship traffic, can limit target detection performance. Few studies have investigated the possibility of enhanced passive acoustic detection in these locations using multiple arrays. Two synchronized 24 element arrays with 300 Hz–50 kHz bandwidth were deployed at the Kilo Nalu Nearshore Reef Observatory (University of Hawaii, Honolulu, HI) in an “L” shape configuration with a vertical array within the 12 m water column and horizontal array orthogonally aligned on the seafloor. This subtropical site is located between Honolulu Harbor and a recreational boating and diving area. Broadband snapping shrimp noise, which dominates the background levels, has a diurnal variation. A series of experiments examined the feasibility of passive acoustic monitoring with array beamforming of a variety of targets including small craft, open circuit scuba divers, and a REMUS autonomous underwater vehicle. The relative performance of narrowband versus broadband beamforming techniques for detection and tracking was quantified for these targets. Moreover, the applicability of nearfield techniques, such as wavefront curvature, was also investigated. [Work supported by the DHS.]