Site Investigations with GPR: Implementation Recommendation (7-4906-S)

The use of air-launched ground penetrating radar (GPR) is well established within the Texas Department of Transportation (TxDOT). The limitation of this technology is that the depth of penetration is limited to the top 2 feet of pavement structure. Ground-coupled GPR has been used in Texas primarily for localized defect detection (such as locating buried tanks or subsurface springs). The ground-coupled GPR systems have a distinct advantage in that they can penetrate much deeper into the structure and provide meaningful information about changes in sub grade layers. In the initial phase of the research, the Texas Transportation Institute (TTI) developed a field test unit which was capable of simultaneously collecting both air-launched and ground-coupled data. The biggest problem with GPR is in the area of data processing. Data collection is relatively straightforward, but the challenge is in converting the acquired GPR signals into information of use to pavement engineers. To achieve this, TTI used two "state of the art" GPR signal processing packages: first, the COLORMAP system, which has been used extensively in Texas for processing air-coupled GPR data; and second, the Road DoctorTM package, which was developed in a joint effort between the Finnish National Roads Administration (FinnRA) and Roadscanners Inc.