Pseudo 3D Imaging of Dielectric and Magnetic Anomalies from GPR Data

This paper deals with the reconstruction of buried targets exhibiting both dielectric and magnetic characteristics, starting from GPR data collected at the interface air/soil. The problem is tackled under the Born approximation. In particular, two-dimensional migration and linear inversion results will be compared versus experimental data and three-dimensional representations of the reconstructions achieved from both methods will be shown. 1. Introduction GPR data processing has been historically focused on dielectric anomalies [1, 2], whereas the magnetic properties of the targets and of the embedding medium are customarily neglected. Recently, it has been outlined that the anomalies and/or the background scenario can exhibit magnetic properties, even in the radio-frequency and microwave range [3–9]. For this reason, in previous papers [10, 11] the problem of the estimation of dielectric and magnetic anomalies has been theoretically studied. It has been worked out that, at least within a 2D linear inversion model, based on the Born approximation and specifically referred to common offset GPR prospecting, the magnetic nature of the targets is not retrievable in absence of a priori information. Therefore, if one is interested in discriminating whether the targets have or not magnetic properties, either a more complicated model (where nonlinear effects and/or polarization effects are accounted for) or further measurements (i.e., not only GPR data) are useful. The theoretical demonstration passes through a long series of mathematical passages and will not repeated here. In [12], experimental data with magnetic targets have been gathered and processed for the first time. In that occasion, however, only four B-scans on the targets were gathered. In this paper, we present reconstruction results by considering a measurement survey on a more complete grid in order to achieve pseudo 3D reconstructions with a specific focus on the depth slices. In particular, we have made use of a tank filled with sand, which was relatively wet at the time of the first measurements (exploited in [12]) but was quite drier when we have gathered the data shown here. The paper is organised as follows. In Section 2 we present the generalized two-dimensional scalar scattering equations, relative to dielectric and magnetic objects embedded in a dielectric and magnetic (possibly lossy) soil. In Section 3, we briefly resume the theoretical discussion about the expected effects of the possible magnetic properties of the buried object on the reconstruction. In Section 4 the experimental