Focusing and Polarization Fusion Imaging in VTI and HTI Anisotropic Media With Dual-Polarimetric GPR Antennas

Uniaxial anisotropy and its dependence on the polarization of electromagnetic (EM) waves have been observed in several types of media within the frequency band of ground-penetrating radar (GPR). However, the specific GPR imaging method in uniaxial anisotropic media has not been well developed. This article proposes a focusing and polarization fusion imaging (FPFI) method for two kinds of the most common uniaxial anisotropic media, i.e., vertical transverse isotropy (VTI) media and horizontal transverse isotropy (HTI). Based on the propagation features of horizontal (H) and vertical (V) polarized waves, we first derive the focusing formulas for signals acquired by HH and VV polarimetric antennas. Subsequently, the stacking path shift (SPS) method incorporating a depth compensation increment (DCI) is proposed to suppress the distortions caused by the discrepancy between velocities in the real media and the correct velocity for the signals on the radargrams. Finally, different polarization fusion (PF) methods for VTI and HTI media are proposed to extract the similarity signals in the focusing imaging results of HH and VV data and suppress the clutter interference. These new theories constitute the proposed FPFI method. Three numerical examples with different complexities and a real experiment verify the effectiveness of the proposed FPFI method. This technology is significant in the detection of textured materials like wood or layered media like ice or vadose zones in the soil.