Discontinuity characterization by the inversion of the spectral content of ground-penetrating radar (GPR) reflections -: Application of the Jonscher model

We compare the spectral ratio between measured reflected wavelets and a reference wavelet for the case of thin-layer reflectors to estimate the frequency-dependent dielectric permittivities of the reflectors and their thicknesses. We use a grid-search algorithm to estimate the permittivity model and the thickness that minimizes the misfit between theoretical and measured ground-penetrating radar (GPR) data and the Jonscher law to model the frequency dependence of the effective dielectric permittivity. We test this inversion method on two sets of high-frequency GPR data recorded on metric-scale laboratory models characterized by discontinuities with different thicknesses and different filling materials. When the ratio of the dominant wavelength of the GPR pulse to the thickness of the layer is less than four, the inversion provides satisfactory values for the electric parameters and thickness of the discontinuity. If the ratio is greater than four and the reflection coefficient varies weakly within the considered frequency range, either the thickness or the permittivity must be known to obtain reliable results for the other parameters. Given this limitation, the spectral analysis of a radar reflection provides a reliable characterization of the discontinuities.