Journal of Microwave Power and Electromagnetic Energy (JMPEE)
TITLE	Radio-Frequency Imaging in Geophysical Applications [PDF]
AUTHORS	C. A. Balanis, R. D. Radcliff and H. W. Hill 1983 18 1 83-94
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Abstract X-ray reconstructive imaging (tomography) has found an incredible range of applications, from microscopy to astrophysics. Radio-frequency imaging has a similar potential which has not yet been fully realized: geophysical uses alone include exploration, mining, and underground process monitoring. Reconstructive imaging to date has been largely based on the explicit assumption of straight line propagation between source and receiver. This is much more valid for X-rays than for radio waves in an underground environment, and the relative lack of success of RF imaging can be largely attributed to this simplification. In this paper, a geophysical imaging technique is being proposed which reconstructs the unknown environment from cross-borehole measurements of RF electromagnetic wave transmission. Unlike some previous methods which assume straight-ray transmission, the technique explicitly accounts for refraction and first-order reflection in the reconstruction process. Several examples of images of underground structures are presented to demonstrate the accuracy and resolution of the method.