Frequency Dependence of the Soil Electromagnetic Properties Derived from Ground-Penetrating Radar Signal Inversion

Abstract

The accuracy at which the subsurface electromagnetic properties can be identified from full wave inversion of ground penetrating radar (GPR) signals relies on the appropriateness of the model describing their frequency dependence. In this paper, we focus on the characterization of the frequency dependence of the dielectric permittivity and electric conductivity of a sandy soil subject to different water contents from inversion of GPR measurements. Based on previous studies of Lambot et al. the methodology relies on an ultrawide band (UWB) stepped-frequency continuous-wave (SFCW) radar combined with an off-ground monostatic transverse electromagnetic (TEM) horn antenna. Forward modeling of the radar signal is based on linear system transfer functions for describing the antenna, and on the exact solution of Maxwell's equations for wave propagation in a horizontally multilayered medium representing the subsurface. Model inversion, formulated by the classical least-squares problem, is carried out iteratively using advanced global optimization techniques. The frequency dependence of the electromagnetic properties of the sandy soil is characterized by performing inversions of the radar signal in different and subsequent limited frequency bands, in which the electromagnetic parameters are assumed to be constant. We observed that over the entire frequency band considered in this study (1-3 GHz), the dielectric permittivity of the *To whom all correspondence should be addressed. 74Lambot, van den Bosch, Stockbroeckx, Druyts, Vanclooster, and Slob sand remains constant with frequency, whatever the water content is. In contrast, the electric conductivity increases significantly from 1GHz to 3 GHz, and this effect increases with water content. The frequency dependence of the electric conductivity may be adequately described using a simple linear relationship. This approach is advantageous since it limits the number of parameters to be optimized in the inverse modeling procedure.

Reconstruction of sub-wavelength fractures and physical properties of masonry media using full-waveform inversion of proximal penetrating radar

“…Similar to results obtained by Lambot et al (2004b) for a sandy soil, we observed that the frequency dependence of the materials electric permittivity is negligible. However, the electrical conductivity, as clearly illustrated in Section 4, shows a frequency dependence that can be locally approximated by a linear equation (Lambot et al, 2005) in the 3-8 GHz frequency range:…”

Joint geophysical measurements to investigate the Rossano of Vaglio archaeological site (Basilicata Region, Southern Italy)

“…The GPR prospecting is mainly applied to solve engineering and environmental problems (Lambot et al, 2005;Steeples, 2001 and reference therein) and to support archaeological prospecting Nuzzo et al, 2002;Piro et al, 2003;Piscitelli et al, 2007;Rizzo et al, 2005). It can be considered as a powerful tool for detecting and imaging shallow subsurface targets characterised by dielectric and conductive properties that are very different from the surrounding ground.…”

Soil Chemical Pollution, Risk Assessment, Remediation and Security

“…Both phase and amplitude information is inherently used for model inversion, thereby maximizing information retrieval from the available radar data, both in terms of quantity and quality. The technique has been successfully validated in a series of hydrogeophysical applications (Lambot et al, 2004a(Lambot et al, , b, 2005(Lambot et al, , 2006a. Recently, we integrated the method with hydrodynamic modeling to retrieve the soil hydraulic properties from otherwise (Lopera et al, 2007a, b).…”

“…Differences were partly attributed to the different operating frequency ranges of both systems (TDR and GPR) and to the different measurement scales. The estimation of the electric conductivity and its frequency dependence was performed simultaneously, which is particularly analyzed in (Lambot et al, 2005). We observed that for the specific sand under investigation and in the limited frequency range 1-3 GHz, the frequency dependence of the dielectric permittivity was negligible and the frequency dependence of the electric conductivity could be described by a linear model, parameterized using only two parameters to invert for.…”