Subsurface fracture measurement with polarimetric borehole radar

In this paper, a full-polarimetric borehole radar system is presented with combinations of dipole antennas and axial slot antennas and is applied to s ubsurface fracture measurement, First, to determine a scattering matrix fro m measurements with antennas having different antenna transfer functions be tween orthogonal polarizations, we present an antenna compensation algorith m that is achieved by an inverse filtering method with the antenna transfer functions experimentally determined by crosshole measurements. The results of crosshole and single-hole measurements carried out in granite at the Ka maishi Mine are shown to verify the proposed method. In the crosshole measu rement, we find that the used dipole and slot antennas have almost the same radiation pattern and frequency dependency from 50 to 120 MHz. The transmi ssion matrices through the host rock are the unit matrix for most paths, wh ile depolarization is observed in some sections. Reflections from subsurfac e fractures show significant depolarization in the polarimetric single-hole reflection measurements. Using the scattering matrix, it is evaluated that subsurface fractures have a randomly isotropic rough surface for wavelengt hs between 1 and 2 m on the rotation of polarization basis.