Analysis of GPR early-time signal features for the evaluation of soil permittivity through numerical and experimental surveys

Recently, various studies have been carried out in order to address the possible relationships between amplitude attributes of the "first-arrival direct wave" (the so-called "early-time signal," ETS), propagating at the interface in bistatic ground-penetrating radar (GPR) configurations, and the relevant shallow-soil permittivity parameters (dielectric constant and conductivity). In this frame, ad hoc compared numerical analyses and experimental investigations are extensively developed and discussed here, with the aim of making clearer the distinctive features and the reliability of this technique. The accurate results achieved for the ETS behavior as a function of various GPR system parameters enable us to identify both which are the more revealing signal attributes able to give predictable correlation with the ground permittivity values and the degree of complexity of the functional relationships between ETS amplitude and system parameters. A number of indications and perspectives are, thus, outlined in order to elucidate features, potential and critical aspects of the ETS technique for effective geophysical applications.