Loss tangent estimation from ground-penetrating radar data using Ricker wavelet centroid-frequency shift analysis

A novel method to estimate the loss tangent using ground-penetrating radar (GPR) data and assuming a Ricker wavelet as the transmitted radar signal is presented. This method proposes a new relation between centroid frequency and loss tangent, which allows retrieval of the loss tangent of a material through a probabilistic inversion approach. The reliability of the results is carefully evaluated by performing an uncertainty analysis that accounts for the white Gaussian noise affecting the radar data. The method is validated in low- and high-loss scenarios, using synthetic data generated by a well-established finite-difference time-domain model (gprMax). The simulations are performed assuming a dipping sharp reflector separating two materials with different electric properties. The loss tangent values retrieved using the centroid-frequency method are compared, for different levels of noise, with those estimated using the maximum frequency method. The results find that the centroid-frequency method is, in general, more precise when the noise level is high, and it is more accurate in a high-loss environment. Finally, the new approach is applied to real GPR data collected with 500 MHz and 1 GHz antennas on a volcanic ash deposit on Mount Etna (Italy), using the signal reflected from a sloping interface separating two distinct volcanic ash layers.