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


Image of FIG. 1.
FIG. 1.

Coverage of the acoustic tripwire for only four acoustic elements spanning the whole water column on each side of the harbor entrance, for isovelocity (top) and two-layer (bottom) environments. Although the propagation structure is modified, the mesh of the net remains unchanged.

Image of FIG. 2.
FIG. 2.

Identification of the rays crossing a single target (top) and two targets (bottom). Both targets are diameter spheres, arbitrarily placed at range and depth, and at range and depth.

Image of FIG. 3.
FIG. 3.

Simulated ambiguity images for one (left) and two (center) targets for an isovelocity (top) and a two-layer (bottom) environment. The shading coefficient is arbitrarily set to 20% for each ray, and the contrast coefficient to 4.

Image of FIG. 4.
FIG. 4.

The experiment configuration, not drawn to scale. The water depth is . The 12 transducer array (SRA) spans of the water column. The 16 hydrophone VRA spanned of the water column. The two arrays were cabled to a common data acquisition point aboard a ship. The coverage (or acoustic “net”) of the tripwire is superimposed on the set-up, considering only the rays which have a total number of two bounces on the interfaces. The limited number of sources and receivers impacts the quality of the coverage.

Image of FIG. 5.
FIG. 5.

Experimental losses observed during the BARRIER04 sea trial. The losses are displayed for the 12 elements of the source array (left) and for the 16 elements of the receiver array (right), for direct path, bottom (“bot”), surface (“surf”), bottom then surface (“bs”) and surface then bottom (“sb”) bounced rays. The target was crossing the tripwire around . In each case, a loss of energy is clearly shown for some elements and some acoustic paths.

Image of FIG. 6.
FIG. 6.

The 6 above plots represent experimental and theoretical ambiguity images (in dB) obtained for the BARRIER04 sea trial set-up. The left column shows the simulated images. The right column corresponds to the real data. Each pair (theoretical and real in a row) corresponds to a specific range and depth combination of the target: depth and range (top), depth and range (middle), depth and range (bottom). The underwater target is a diameter sphere, and the contrast coefficient is chosen . The theoretical image has been calculated including a diameter surface buoy located at the same range, from which the target was suspended.


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