Determination of the stability of a pulse GPR system and quantification of the drift effect on soil material characterization by full-wave inversion

Time and amplitude drift is a common problem for some time-domain radars. Some corrections have been suggested for far-field radar data, but due to the coupling effect, there is no equivalent for near-field radar data. In this paper we first quantified, considering the occurrence of the first reflection peak, the time drift of a 900 MHz center-frequency pulse radar system over a certain time period (28 hours non consecutive in identical situation). The maximum time drift was 0.0978 ns. Second, in the frequency-domain, we characterized the maximum time and amplitude drift via the calculation of a frequency-dependent ratio to multiply to the original signal to illustrate the effects of the drift. Third, we measured the sensitivity of the soil material characterization by full-wave inversion in response to a drift. For the inversion problem, we used a new near-field model taking particularly into account the antenna-medium coupling through antenna characteristic global reflection and transmission coefficient functions. The overestimation of the dielectric permittivity may reach 50% for low values of the dielectric permittivities, and the underestimation 25% for higher values, following a gradient. The errors on the estimation of the electric conductivity is much higher reaching an extreme 10^5.4% for the lowest original values, with an average of 10^2.5%. The differences in the estimation of these two parameters have been explained through a sensitivity analysis. Indeed, the lower sensitivity of the electric conductivity leads to higher errors than for the dielectric permittivity.