Chapter 19: Fracture Imaging and Saline Tracer Monitoring by Crosshole Borehole Radar
Crosshole electromagnetic techniques have been studied for detection and imaging subsurface anomalies. The use of higher frequency, i.e., radar, has high resolution, and has been used for imaging anomalies having high contrasts with the host rock. For example, Litle et al. (1979) and Lee et al. (1989) used crosshole radar to detect voids or tunnels, Lager and Lytle (1977) used tomography to visualize trace flow, and Park et al. (1998) used tomography for imaging voids. Borehole radar tomographic analysis has been applied to various other fields (Olsson et al., 1992; Mathisen et al., 1995; Lane et al., 1996; Wright et al., 1998). In most cases, crosshole tomography enables us to characterize subsurface media between two boreholes very well.
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Near-surface geophysics uses the investigational methods of geophysics to study the nature of the very outermost part of the earth’s crust. Man interacts with this part of the earth’s crust: he walks on it; he drills and excavates into it; he constructs structures on and in it; he utilizes its water and mineral resources; and his wastes are stored on and in it and seep into it. The very outermost part of the Earth’s crust is extremely dynamic-in both technical (physical properties) and nontechnical (political, social, legal) terms-which leads to both technical and nontechnical challenges that are much different than the challenges faced by “traditional” applications of geophysics for regional geologic mapping and for oil and gas exploration (see Chapter 2).