Suppression of Clutters Caused by Periodic Scatterers in GPR Profiles With Multibandpass Filtering for NDT&E Imaging Enhancement

Many civil infrastructures contain periodic elements for the purposes of foundation support or strength reinforcement. Good examples are the sleepers for rail track support and the rebars in reinforced concrete structures. For engineering nondestructive testing and evaluation (NDT&E) using ground penetrating radar (GPR) these periodic elements in the near subsurface act as scatterers that generate clutters in GPR profiles and mask the signature of the targets and hinder GPR's capability in defect detection and characterization. In this paper, we develop an algorithm using multibandpass filtering (MPF) technique to suppress the clutters in GPR profiles caused by periodic scatterers. We first extract the spatial information of the periodic scatterers and carry out spectral analysis to characterize the clutter energy in multiple wavenumbers. Then, we use this information to design the MPF in wavenumber domain and execute the filtering back in space domain with proper windowing. We test the effectiveness by applying the algorithm to a synthetic data set that simulates GPR survey on a railway system. The filtering results are very encouraging. We also apply MPF to the field GPR data collected on the Tibetan Railway. A fouled area in the ballast can be much clearly visualized than in the original, clutter-masked GPR profile. We also apply MPF in steel bar reinforced concrete slab and compare the results with the redatuming and migration methods. The MPF appears superior in clutter suppression caused by periodic scatters. MPF provides a practical and effective way to enhance GPR imaging in engineering NDT&E.