Detection and identification of potential land mine hazards by waterjet use

The impact of a waterjet stream emits an acoustic signal when the jet strikes a buried target object. The structure of the sound emitted depends on the energy in the jet, the target which is struck, and the surrounding media. A high pressure (less than 5000 psi) waterjet of diameter 0.01 inches can penetrate into the ground to a depth of greater than 8 inches in less than 0.02 seconds and will generate a distinct acoustic signal from any obstruction it encounters as it makes that hole. By analyzing the sounds generated from a series of jets, located at 2 - 3 inch intervals over the path width of a remotely controlled detection unit, it is possible to identify the location of suspicious objects ahead of a vehicle. Flow rates for such a system, which can cover a path width of 36 inches at walking speeds, are anticipated to be around 5 gallons per minute. We have made initial measurements on acoustic signals generated by waterjet impact and found that the response from buried land mines appears to be Gaussian, thus allowing second order statistics to characterize the signals. We have shown that under laboratory conditions, the power spectrum can be used to discriminate land mines from other underground objects such as rocks and metal pipes.