A computer program, called TERRA (Thickness Evaluation of Roads by RAdar) was recently developed for estimating pavement layer thicknesses from ground penetrating radar (GPR) data. This program incorporates decision criteria for automated detection of layer interfaces, computation of layer thicknesses and a segmentation algorithm for delineating segments based on layer thicknesses. The Florida Department of Transportation (FDOT) initiated the present field study for an initial assessment of TERRA. Radar and core data were collected from several flexible pavement sections of Florida's roadway system. These sites were selected to represent the present Florida in-place mixes (Superpave and Marshall mixtures) and different asphalt layer thicknesses, which varied from approximately 50 to 300 mm (2 to 12 in). Radar data were collected at both highway speeds and in stationary mode. This paper presents a description of the data collection effort as well as the subsequent analysis and findings.
To address the need for developing a database of pavement layer thicknesses to support pavement management, the Florida Department of Transportation (FDOT) funded a project with the Texas Transportation Institute that developed a computer program called TERRA for analyzing Ground Penetrating Radar (GPR) data in a production environment. TERRA is an acronym for Thickness Evaluation of Roads by RAdar. It incorporates user-specified decision criteria for automated detection of layer interfaces. Tests to verify peak tracking capability demonstrated that the program is able to handle gradual or sudden changes in the patterns of the interface reflections as well as gaps in the data. Verification of the thickness predictions against core data from sites surveyed with radar showed acceptable accuracy for uncalibrated estimates of surface thickness. In particular, the average of the absolute differences between the means of predicted and measured surface thicknesses was found to be 0.30 inches. Because of the absence of measured base thicknesses, it was not possible to verify the base predictions on the sites tested. It is recommended that this be done by FDOT at a future date as part of its GPR implementation efforts.