Road managers can easily acquire underground records in a long distance by using ground-penetrating radar (GPR) equipment with high-speed scanning, but many records show poor quality of imaged sections in shallow depths near the road surface. When you utilize GPR records for the management of paved roads, subsurface events of reflection waves must be analyzed with adequate quality. NMO (Normal MoveOut) correction is one of an effective processing and it can be applied using a set of multi-offset GPR data at a scan. NMO correction requires velocity profiles and velocity analysis is another effective processing for road assessment. Modifying locations of transmitter and receiver antennas are also an important procedure before applying a series of velocity analysis and NMO processing for GPR. We demonstrate to detect the boundary between an asphalt concrete mixture and a road base, even if the central frequency of GPR is below 1 GHz. In addition, we proposed automatic and stable velocity analysis for road assessment using GPR. |