Borehole radar performance characteristics and applications for underground change detection

Low-frequency borehole radars have proven useful in recent years as tools for locating underground features, such as rock fissures and voids. In fact, these radar systems are now commercially available at multiple operating frequencies. Most of the borehole radar applications to date have utilized the systems in a tomographic mode because of its capability to locate a target between two boreholes. In this paper, we focus on the use of a borehole radar system in a reflective mode because of its capability to detect a target anywhere in the vicinity of the radar. As expected, the detection range of the system is severely limited due to two-way attenuation through the earth. Nonetheless, we show that it is possible to form a roughly focused range-vs.-depth image of the region surrounding the borehole. More importantly, by developing and implementing some straightforward signal processing techniques, we are able to detect the introduction of a target into an adjacent borehole in both the focused and the unfocused imagery.