Application of a SAP-DoA method to GPR data for the location of reinforcing elements in concrete

A Sub-Array Processing approach was recently developed and implemented by the Authors, to detect targets lying in the near field of an antenna array. In such method, an array of receivers is partitioned in sub-arrays; for each of them, the number of incoming signals and their directions are predicted by using Direction-of-Arrival algorithms. In this paper, the technique is revised and extended to the case of ultra wideband signals, in order to investigate its applicability to Ground-Penetrating Radar (GPR) data processing. Tests are performed on reference synthetic data, calculated by using a freeware tool implementing the finite-difference time-domain method and included in the database of COST Action TU1208 "Civil engineering applications of Ground Penetrating Radar." In particular, three concrete cells are considered: the first cell hosts five circular-section steel rods, with different radii and positions, in the second cell four metallic and dielectric rods are embedded, in the third cell an angle bar, a box section and a u-channel are present. The first and second tests aimed at demonstrating the capability of the procedure to correctly locate multiple objects in concrete. The third more ambitious test aimed at verifying whether the procedure could distinguish between different shapes of typical reinforced concrete elements. This work was carried out within the Short-Term Scientific Mission COST-STSM-TU1208-26649. The paper is concluded with a brief overview of the activities carried out within Working Group 3 of COST Action TU1208, dealing with the development of electromagnetic modelling, imaging, inversion and data-processing tools for GPR.