Background of ground penetrating radar measurements

Characterization of the shallow subsurface (0.25 to 10 m) is of growing imp ortance for engineering activities, solutions of environmental problems, an d archaeological investigations. Ground-penetrating radar (GPR) is an appro priate technique considering the depth range of interest, the strength of e lectric and magnetic contrasts between different subsurface layers and buri ed objects, and the required resolution. GPR surveys can detect subsurface structures by recording electromagnetic reflections from discontinuities. T he detectability of objects and the delineation of subsurface structures in creases with increasing wave velocity and conductivity differences between the object and its surroundings or between adjacent layers. However, unwant ed reflections from objects above the surface influence the images. Shielde d antennas can be used to avoid strong reflections from these objects. The data thus obtained are, however, more difficult to interpret. The fundament als of GPR and two different acquisition setups for a GPR system are discus sed. Basic interpretation tools for travel-time and velocity estimation are described, and finally, case studies are presented, followed by conclusion s.