Potential of a Dual-polarization Ground Penetrating Radar for Underground Cylinder Diameter Estimation

Ground Penetrating Radar (GPR), as a recognized non-destructive testing (NDT) technique, has been widely used in civil engineering due to its advantage of high efficiency and good resolution. Polarimetric GPR has been proved to possess an improved ability to detect and characterize the properties of underground cylinder than the conventional single-channel GPR. This study investigates the potential of a dual-polarization GPR system to estimate the diameter of underground cylinder through analytical analysis and a laboratory experiment. Using a plane wave source, we derived analytical solutions for signals scattered from a cylinder. Subsequently, we calculated the backscattering coefficients for both the perpendicular broadside mode (HH) and parallel broadside mode (VV) from these solutions. We observed that both the relative scattering coefficient and the phase difference decrease with the diameter-to-wavelength ratio, particularly in the 0–0.35 range. Building on this insight, we propose a method to estimate the diameter of underground cylindrical bodies based on the phase difference. Laboratory experiments conducted with a commercial dual-polarization GPR system demonstrated that the diameter estimation error is less than 1.6mm. This study provides preliminary evidence that the phase difference in dual-polarization radar signals can effectively determine the diameter of buried rebars in underground cylinders.