Three-dimensional advanced tomographic procedure for the imaging of metallic and dielectric targets through GPR data

The tomographic algorithms commonly used to process ground penetrating radar (GPR) data assume the scattering phenomenon activated by ideal sources. This can be considered an adequately accurate assumption if the actual GPR antenna presents almost nondirectional features, but should instead properly revisited when a target is illuminated by means of more collimated near-field distributions. In this work, moving from the recent advancements done for two-dimensional scalar GPR imaging theory, we propose a three-dimensional (3-D) vector formulation of the scattering equation, modeling the incident field with the actual field radiated by a directional antenna. Both 3-D dielectric and metallic targets are reconstructed in challenging environments by considering multi-frequency data at microwaves. A comparative analysis is developed through the processing of numerical data by means of a singular-value decomposition as well as an adjoint-operator scheme. The effectiveness of these methods is assessed considering full-wave synthetic data generated on a customized virtual setup based on a commercial tool.