Abstract:

A system has been designed for the detection of buried landmines. The system uses a stationary seismic source in conjunction with a movable displacement sensor that is based on an 8 GHz CW radar. The sensor measures the surface displacement by analog demodulation of the radar signal, which is reflected from the soil surface and modulated by the surface motion. The sensor is not in direct contact with the soil surface and is, therefore, capable of interrogating surface motion immediately above a buried mine. This configuration provides the dual advantage of removing half the seismic propagation path that would be encountered with a classical pulsed echo technique and detecting localized fields that would not propagate to a remote receiver. The system has been used in the laboratory to image inert antipersonnel mines and simulated antitank mines buried in damp compacted sand. Signal processing in the wave number domain provides significant improvement in the contrast between mine-related and background motion. The simplest detection cue for antipersonnel mines was found to be low-frequency resonances of their trigger mechanisms. These responded to seismic excitations with substantial local displacement. The resonances made these mines easily discernable from buried clutter such as rocks and sticks. [Work supported by ARO.]