Over the past three years a system has been under development at Georgia Tech that utilizes a seismic interrogation signal in combination with a non-surface-contacting, radar-based displacement sensor for the detection of buried landmines. Initial work on this system investigated the workability of the system concept. Pragmatic issues regarding the refinement of the current experimental laboratory system into a system which is suitable for field testing and, in turn, one which would be suited to field operations have been largely ignored until recently. Both field operations and realistic field testing require a system that is different from the original laboratory system in two crucial ways. One of these is that a field system needs a sensor standoff from the ground surface larger than the original 1 to 2 cm. This is necessary in order to account for small-scale topography, to avoid ground cover such as grass, and to minimize the risk to the operator. A second difference is that the scanning speed of a field system must be substantially greater than that of the original laboratory system, which takes several hours to image 1 m2 of ground surface. From an operational standpoint, the reason for this is obvious. From an experimental standpoint, it is also important because ambient conditions are difficult to control on long time scales outdoors. Both of these new requirements must be met within the design parameters that were established empirically during the development of the laboratory system. One of these is that the system must be capable of measuring peak displacements as small as 1 nm with a 1 Hz resolution band in the low audio frequency range (30 Hz to 2 KHz). This is necessary because of limits placed by the medium on the amplitude of seismic signals that can be generated. Another parameter is that the measurement must be integrated over a region with a diameter of about 2 cm to 5 cm on the ground surface. This is necessary in order to preserve spatial structure of interest for the imaging of small mines. An array of radar-based displacement sensors configured with focused antennas meets all these requirements. A sensor was designed to test this concept. The new sensor was equipped with an antenna consisting of a conical corrugated horn and a bifocal dielectric lens that permitted a 20-cm surface-standoff distance. The sensor was tested in a laboratory experimental model in scenarios similar to those used to evaluate the original system sensor and was found to satisfy all of the new system requirements.
Use of high-frequency seismic waves for the detection of buried land mines
2001
10 Seiten, 9 Quellen
Conference paper
English
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