An active acoustic tripwire for simultaneous detection and localization of multiple underwater intruders

Abstract

An algorithm allowing simultaneous detection and localization of multiple submerged targets crossing an acoustic tripwire based on forward scattering is described and then evaluated based upon data collected at sea. This paper quantifies the agreement between the theoretical performance and the results obtained from processing data gathered at sea for crossings at several depths and ranges. Targets crossing the acoustic field produce shadows on each side of the barrier, for specific sensors and for specific acoustic paths. In post-processing, a model is invoked to associate expected paths with the observed shadows. This process allows triangulation of the target's position inside the acoustic field. Precise localization is achieved by taking advantage of the multipath propagation structure of the received signal, together with the diversity of the source and receiver locations. Environmental robustness is demonstrated using simulations and can be explained by the use of an array of sources spatially distributed through the water column.

Analysis of the arriving-angle structure of the forward scattered wave on a vertical array in shallow water

“…Numerical experiments are conducted in a Pekeris waveguide, which consists of a layer of water 100 m deep with constant sound speed of 1500 m/s overlying a half-space bottom: muddy sand, with density q b ¼ 1.806 g/cm 3 , sound speed c b ¼ 1668 m/s, and attenuation coefficient a ¼ 0.692 dB/(mÁkHz). 13 A broadband impulse with central frequency 0.5 kHz and bandwidth 0.1 kHz, is emitted by the point source.…”

“…By exploiting the time reversal mirror technique, Song et al 2 set up a high-frequency underwater acoustic barrier, which was able to detect an intruder in the quiescent region because of the acoustic energy enhancement. Folegot et al 3 proposed a ray model-based algorithm that allowed simultaneous detection and localization of multiple submerged targets crossing a short acoustic barrier. In addition, they conducted a verification experiment by using the data collected at sea.…”

Target detection and localization in shallow water: An experimental demonstration of the acoustic barrier problem at the laboratory scale

“…Recently, some studies on target detection and localization have been published using a beamforming technique on a receiver array placed in front of some acoustic sources (Folegot et al, 2008). The presence of the target was detected through the shadowing effects observed on a set of beamformed beams.…”

Forward acoustic scattering by moving objects: Theory and experiment

“…Forward scattering from an intrusive object could cause aberration in the waveguide response, providing an advantage in quietobject detection [5][6][7][8]. Transient aberration results from interference between the incident and scattered fields from an object [9], and its features can be actually difficult to be predicted in a multipath environment.…”

“…A detection and localization algorithm based on the same techniques was described and evaluated based upon the experiment in a harbor environment [7]. Song et al [8] proposed an active time reversal approach, where variations caused by a crossing target were observed as rising levels in the side-lobes near the focal zone.…”