Innovative GPR for pavement inspection

A new ground penetrating radar system was built using a controllable variable pulse-width transmitter and a new antenna design. The transmitter generates monocycle pulses with pulse widths that are continuously variable from 0.5 to 2 nanoseconds; thus, the center frequency of the pulse spectrum is variable from 500 to 2000 MHz. The antenna is relatively small and light weight and operates in both the air-coupled and ground-coupled mode. The complete prototype system including radar control unit, antenna unit, lap-top computer, battery, and back-pack, weighs 65 pounds, is portable and easily usable by one person. The software developed for this new GPR includes a menu driven, user-friendly interface for selecting an operating frequency from 500 to 2000 MHz and an automatic data interpretation algorithm. Hardware and software development focused on a GPR system for evaluating pavement systems and to automatically measure pavement thickness. Other GPR applications are readily apparent. A Neural Network was trained to interpret the radar data in real-time and display pavement thickness as the operator is scanning the pavement. Field test results demonstrate that the prototype GPR can measure asphait pavement thinner than 4 cm (at 2000 MHz) and can penetrate sandy soils to depths greater than 5 meters (at 500 MHz). This GPR system replaces other radar pavement-evaluation systems that require multiple antenna/transmitter units to accomplish the same range of measurements. The design concepts embodied here are scalable to other extended frequency ranges, e.g., 50 to 200 MHz for geologic surveys with a single antenna/transmitter unit.