Determination of velocities with radar in road layers

In order to calibrate the radar equipment and to perform measurements in well controlled conditions, a test site was constructed in the hall of BRRC. On this test site, 4 different road configurations are built (asphalt layer on concrete plates, asphalt layer on lean concrete, concrete layer on lean concrete separated by a thin layer asphalt and asphalt covering cobblestone). An unbound aggregate layer serves as a base layer. Pipes and cables were buried in the structure and other defaults. The site is instrumented with temperature and strain gauges. During the construction, geotechnical measurements and control of density were performed. Radar measurements were performed on the test site with the BRRC radar equipment (2 GHZ GSSI horn antenna, 1 GHz GSSI horn antenna and 400 MHz GSSI contact antenna). Three different approaches were used to estimate the velocity of radar waves in the first road layer. The first approach consists in calculating the velocity using the real layer thickness and the measured two-way times. The second approach consists in using the GSSI software calculating automatically the velocities. The third approach is based on the analysis of the reflection on the surface, which is compared to a calibration signal. This paper presents the three approaches.