ANALYSIS OF A BOREHOLE RADAR IN CROSS-HOLE MODE

We present a theoretical approach to the cross-hole radar measurements. An approximate analytical form for the current distribution on an antenna in a borehole is derived and the theoretical receiving signal of borehole radar in the cross-hole measurement is calculated. Theory is compared in the time-domain with the measured borehole radar signal obtained in a salt deposit. The radiation pattern of a borehole radar excited by a pulse is discussed. The accuracy of tomographic analysis, which is often applied to the cross-hole radar measurements, is strongly governed by this radiation pattern. We found that in practice, most borehole radars have a pattern of a lambda/2 dipole antenna. However, we pointed out that the radiation pattern can be deformed by short pulse excitation, loading by the surrounding media, and coupling to the logging cable.