Polarimetric borehole radar information can be obtained from a combination of co-polarization and cross-polarization reflection measurements in a borehole. Most conventional borehole radars use axially-oriented electric dipole antennas for transmission and reception, resulting in a response only to the co-polarized signal component of the a reflected wave. However, more information can be obtained if the cross-polarized component of the reflected wave is also measured. Cross-polarization borehole radar measurements are presented in which an axiallyoriented slot antenna is used as the receiving antenna and an electric dipole is used as the transmitting antenna. The antenna was excited by a short DC pulse to obtain broadband pulse-echo operation. Measured signals were transmitted through a broad-band optical signal link. Field measurement using the prototype radar sonde was carried out in granite rock. The measured signals showed that detection of the short-range reflections can be improved with crosspolarization measurements since direct coupling between the transmitting and receiving antennas is considerably reduced. We also observed the polarization dependency of a reflectivity of a water containing fracture. For instance, reflection from a layer containing gravels showed significant depolarization. This additional information obtained from the polarimetric borehole radar measurement will give us more knowledge of cracks such as surface roughness and water contaminant.


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