Microwave Interferometric System for bidimensional GPR Positioning

Ground penetrating radar (GPR) systems are sensors that are able to acquire underground images by scanning the surface of the soil/pavement under investigation. Usually, a GPR system records its own position along the scan line, using a mechanical odometer, i.e., a rolling wheel in contact with the ground. This simple and cheap solution can be ineffective on uneven terrains. The most advanced GPR systems make use of global navigation satellite system (GNSS). The GNSS allows to retrieve three dimensional coordinates of GPR with a precision lower than a meter. The main drawback of GNSS is related to the weather condition that can affect the uncertainty. Moreover, the GNSS can not be applied in covered areas (wood, internal space). In this work, a positioning system based on an interferometric radar is presented. The interferometric radar is able to detect small displacements of the targets in its field of view. Such a capability was used to track the GPR position along a line by some of the authors. In this paper the authors generalize the concept by using two couples of antennas connected to the same radar head. This permits to retrieve bidimensional coordinates of the GPR. The system was validated with simulations and tested in a realistic experimental scenario. The GPR has been equipped with a standard target: a naval corner reflector. The two pairs of antennas and the GPR target were fixed at the same heigh in order to define a measurement plane.