This paper describes the OPR system developed and implemented for the Texas Department of Transportation (TxDOT). The system includes a Penetradar PS-24 OPR system together with a data acquisition and signal processing system developed by the Texas Transportation Institute. The entire system is housed in a data acquisition vehicle which also includes distance measuring equipment and a synchronized video recording system. The OPR has been used on several major pavement projects in Texas. The antenna is air launched and suspended between 250 and 350 mm above the pavement and has been shown to operate adequately at close to highway speeds (50 kph). In this paper the signal processing algorithms will be described together with results from a series of case studies. The signal processing system tracks the reflections and measures their amplitudes and arrival times on a trace by trace basis. Methods of cleaning up the signal with end reflection subtraction and of accommodating antenna bounce have been built into the software. From typical OPR reflections from pavements the layer dielectrics and thicknesses can be calculated for a maximum of 4 distinct layers. The moisture content of typical granular base material has been related to the relative dielectric value of the layer. The detection of pavement defects, such as voids, has been related via decision rules to the measured amplitudes, dielectrics and thicknesses and their variance along a highway. Field measurements and ground truth information will be reported on several in service pavements in Texas. These applications include layer thickness determination, void detection and locating areas of asphalt stripping.


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