Albéric De Coster

Fundamental Analyses on Layered Media Reconstruction Using GPR and Full-Wave Inversion in Near-Field Conditions

Multifrequency and multioffset ground-penetrating radar data acquisition modes are used to maximize the information content and parameter retrieval capabilities. However, they also increase the computational cost dedicated to the inversion procedure. In this paper, the impact of the number of frequencies and the multistatic configurations on the information retrieval capabilities is investigated through the response surface topographies of the objective functions. We resort to a full-wave-inversion procedure and a recently developed electromagnetic model which takes advantage of a closed-form solution of Maxwells equations to describe the antenna-medium system. We show with numerical and laboratory experiments the possibility of reducing the number of frequencies from several hundreds to one or several tens of components without affecting the information retrieval capabilities. We also show through several scenarios that the presence of a perfect electrical conductor increases the number of frequencies required to ensure an acceptable retrieval of the subsurface properties whereas the conductivity of the first layer and the relative permittivity of the second layer do not affect it. The results highlight that information content analyses are important in order to study and optimize data acquisition and inversion procedures, and thereby the computation time.

Two-Dimensional Linear Inversion of GPR Data with a Shifting Zoom along the Observation Line

Linear inverse scattering problems can be solved by regularized inversion of a matrix, whose calculation and inversion may require significant computing resources, in particular, a significant amount of RAM memory. This effort is dependent on the extent of the investigation domain, which drives a large amount of data to be gathered and a large number of unknowns to be looked for, when this domain becomes electrically large. This leads, in turn, to the problem of inversion of excessively large matrices. Here, we consider the problem of a ground-penetrating radar (GPR) survey in two-dimensional (2D) geometry, with antennas at an electrically short distance from the soil. In particular, we present a strategy to afford inversion of large investigation domains, based on a shifting zoom procedure. The proposed strategy was successfully validated using experimental radar data.

Impact of the antenna offset and the number of frequencies on layered media reconstruction using full-wave inversion in near-field conditions

Pipes and water leaks can potentially be detected using ground-penetrating radar (GPR). Recently, a new generalized model was developed to quantify the medium electrical properties by full-wave inverse modelling. It takes advantage of a closed form solution of Maxwells equations for describing the coupled antenna-medium system. In this study, we used that model to evaluate the inverse problem for different radar configurations and various multilayered medium layouts. Numerical experiments were performed by generating and inverting synthetic Greens functions in order to show the influence of the antenna offset on the response surface topography of the objective functions. The impact of a reduced number of frequencies on these objective functions was also investigated for a monostatic configuration before combining this approach with a multioffset configuration. The results showed an improvement in the response surface topography when the number of antennas was increased. However, the importance of this enhancement varied according to the number of frequencies taken into account. It also pointed out the possibility of reducing the number of frequencies used for the inversion while preserving the information content. This work highlights the great potential of the model to improve the medium parameter retrieval while reducing the computation time.

Improvement of Ground Penetrating Radar (GPR) Data Interpretability by an Enhanced Inverse Scattering Strategy

This paper is inserted into the framework of inverse scattering with application to Ground Penetrating Radar (GPR) data and is meant to provide a method helping to apply inverse scattering algorithms to electrically large investigation domains. In particular, we focus on the depth slices that are particularly important in application on cultural heritage and propose in relationship with the depth slices a strategy that we will call “shifting zoom” that is specifically a method to mitigate the effects of the limited view angle in the linear tomographic inversion applied to GPR data. In particular, this paper is an extended version of the contribution (Persico et al. in: Proceedings of Imeko international conference on metrology for archaeology and cultural heritage, Lecce, Italy, 2017a), published in the Proceedings of the conference metrology for archaeology 2017. We propose here a validation of the shifting zoom versus experimental data gathered in a controlled test site, and we will show the effect of the shifting zoom on depth slices achieved from these data after a linear inverse scattering processing has been applied for their focusing.