An evaluation of the early-time GPR amplitude technique for electrical conductivity monitoring

In the present paper we use the recently-proposed early-time GPR (Ground Penetrating Radar) amplitude technique with the aim of detecting the variations of electric conductivity in a porous material having a uniform permittivity. A specific laboratory setup has been realised to evaluate the sensitivity of the early-time amplitudes to the variations of the subsurface salt concentration (i.e., conductivity). To assess the capacity of the early-time amplitude to follow the electrical conductivity changes, we compare the early-time results acquired using the envelope of the first part of GPR signals with the concurrent conductivity measured with TDR (Time Domain Reflectometry). The GPR survey has been carried out using a bistatic radar unit (Sensors & Software, Inc) operating at 1 GHz. Further useful information has been derived by suitably implementing a full-wave numerical modelling, able to accurately analyse the features of the waves detected by the GPR with flexible parameterization. Our results indicate that the near-surface electromagnetic properties of the material can be directly extracted from the GPR early-time amplitude technique. In particular, both experimental and numerical data show a very high correlation coefficient between the radar signal amplitude and the TDR-derived electrical conductivities.