Relations between GPR early-time signal attributes and ground permittivity: a numerical investigation

In recent times, various theoretical and experimental studies have been carried out in order to address the relationship between amplitude attributes of the `direct wave' propagating at the interface in bistatic ground-coupled radars (the so-called `early-time signal') and the relevant shallow-soil permittivity. This issue is extensively analyzed here for the first time by means of an accurate and efficient numerical approach based on a CAD tool. The flexibility of the approach allows us to investigate in wider terms the role of the various physical parameters that affect the early-time signal features (type, location, and distance of the antennas, transmitted waveforms, etc.), in addition to the electromagnetic contrast between upper and lower media. Quantitative results are derived in order to clearly establish which are the more revealing signal attributes that enable for predictable correlation to the ground permittivity values and what kind of functional relations can be outlined. Novel and reliable information can thus be achieved on the actual potential of the `early-time method' for efficient subsurface non-destructive testing.