Three-dimensional non-contact subsurface radiotomography through a non-planar interface between media

A fast method is proposed for the reconstructing of three-dimensional images of objects hidden under the non-planar surface of media on the basis of ultra-wideband (UWB) radar measurements of magnitude. It is assumed that the radar moves in the plane above the medium and produces UWB radar measurements with a fixed step. The solution of the inverse problem is made in the single scattering approximation and the approximation of the phase screen for a non-planar surface. The algorithm for reconstruction of the radio image of heterogeneities in the medium is reduced to a three-dimensional fast Fourier transform. This method is verified by numerical simulations and experiments in the frequency range from 4 to 14 GHz. For the experiment a scalar network analyzer was used and only the magnitude of the field was measured. The phase information is retrieved due to the interference of the direct wave from the transmitter and the waves scattered by the heterogeneities of the medium. Using the measured data the three-dimensional image of heterogeneities has been reconstructed.