Comparison of 500 MHz and 2 GHz Air-Launched Ground Penetrating Radar for Complex Pavement Analysis

Ground penetrating radar (GPR) data were obtained along a 29 km (18 mile) stretch of interstate 93 in southern New Hampshire. Eight cores obtained along this segment of highway indicated pavement thickness varying from 7.5 in to 13.5 in (19-34 cm). Four to eight layers of asphalt plus a “penetration” layer consisting of base material saturated with bitumen were detected from inspection of the cores. The GPR data were obtained with 2 GHz and 500 MHz center-frequency horn antennas. The 2 GHz data clearly revealed numerous reflections from the asphalt inner layers. The pavement bottom reflection was often lower amplitude than the inner pavement reflections, making it difficult to assess which reflection was associated with the bottom of the asphalt. In contrast, the 500 MHz horn antenna data yielded relatively higher amplitude pavement bottom reflections and fewer inner pavement reflections.