Pseudopulse Near-Field Subsurface Tomography

Abstract

Decisive success has been achieved in developing the subsurface near-field scanning tomography that overcomes the Rayleigh diffraction limit of a resolution. It is related to the transformation of the multifrequency inverse scattering problem to that for a complex-valued synthesized pulse (pseudopulse). It leads to the integral equation that has maxima in the depth dependence of its kernel and, hence, to the much better depth resolution of tomography. Moreover, the noise related to surface scattering is mainly suppressed in such an approach. This idea is realized here in the microwave subsurface tomography of 3D inhomogeneous dielectric structures. For homogeneous dielectric targets, this approach is applied to obtain holography images of their shape.

Near-Field Tomography and Holography of Low-Contrast Subsurface Objects

“…The developed theory was implemented in numerical algorithms and applied in the experiments, whose first results were published in [4]. The initial data for analysis were the results of measuring complex amplitudes of the signal at 801 frequencies in the range 1.7-7 GHz in the two-dimensional region (x, y) over the probed subsurface inhomogeneity by using an "Agilent E5071B" vector network analyzer.…”

“…For such objects, it is sufficient to solve a simpler problem of reconstruction of the shape of their surfaces, i.e., a computer holography problem [4], by using the solution of the tomography problem ε 1 (κ x , κ y , z) in the k-space, which was obtained from Eq. (10).…”

“…Equation (5) was used in the subsurface tomography algorithms developed in [3] and in tests of multifrequency microwave tomography in [4]. Equation (1) also allows one to determine the kernel of the three-dimensional integral for calculation of the measured signal in Cartesian coordinates within the Born approximation:…”

“…This approach was experimentally realized as a method of subsurface microwave tomography of inhomogeneities in soil [4]. Analyzing the results of the experiment, we faced difficulties in discerning the subsurface scattering signal against the background of strong contribution made by the scattering from the surface.…”

“…However, the determination of the shape (the task of computer holography), based on the results of solving a more general tomography problem, is not a trivial problem, as will be shown in what follows. The approach to solving the problem of holography of such object and the first results are also described in [4]. To a certain extent, similar approaches are currently developed with the purpose of obtaining radio holography images of surfaces of metal inhomogeneities [5].…”