Experimental implementation and assessment of two polarimetric calibration approaches applied for a fully polarimetric borehole radar

A fully polarimetric borehole radar system with four combinations of dipole and cylindrical slot antennas was developed to acquire fully polarimetric datasets in drilled boreholes. This system in conjunction with several radar polarimetry techniques has proved to be a good alternative to physical subsurface fracture characterization. Furthermore, such polarimetry techniques, namely Pauli decomposition, eigenvector-based decomposition, Durden-Freeman decomposition and polarimetric anisotropy parameter methods, can provide comparable performances in terms of fracture characterization and classification. Polarimetric calibration to determine a scattering matrix (Sinclare matrix) is the foremost procedure in the radar polarimetry processing chain. In this paper, we experimentally implement and evaluate two polarimetric calibration approaches, namely (1) cross-hole polarimetric calibration and (2) single-hole polarimetric calibration, utilizing fully polarimetric datasets acquired at a specific borehole test site. Both polarimetric calibration approaches can guarantee the further implementation of radar polarimetry techniques, and especially, the single-hole polarimetric calibration will be very meaningful to practical applications.