Background of ground-penetrating radar measurements

J. van der Kruk; E.C. Slob; J.T. Fokkema

J. van der Kruk Section of Applied Geophysics, Subfaculty of Applied Earth Sciences, Faculty of Civil Engineering and Geosciences, Delft University of Technology, Mijnbouwstraat 120, 2600 GA, Delft, the Netherlands
E.C. Slob Section of Applied Geophysics, Subfaculty of Applied Earth Sciences, Faculty of Civil Engineering and Geosciences, Delft University of Technology, Mijnbouwstraat 120, 2600 GA, Delft, the Netherlands
J.T. Fokkema Section of Applied Geophysics, Subfaculty of Applied Earth Sciences, Faculty of Civil Engineering and Geosciences, Delft University of Technology, Mijnbouwstraat 120, 2600 GA, Delft, the Netherlands

Keywords: field surveys, GPR

Abstract

CharacterizaÍion of the shallow subsurface (0.25 to 10 m) is of growing importance for engineering activities. solutions of environmental problems, and archaeological investigations. Ground-penetrating radar (GPR) is an appropriate technique considering the depth range of interest, the strength of electric and magnetic contrasts between different subsurface layers and buried objects, and the required resolution. GPR surveys can detect subsurface structures by recording electromagnetic reflections from discontinuities. The detectability of objects and the delineation of subsurface structures increases with increasing wave velocity and conductivity differences between the object and its surroundings or between adjacent layers. However, unwanted reflections from objects above the surface influence the images. Shielded antennas can be used to avoid strong reflections from these objects. The data thus obtained are, however, more difficult to interpret. The fundamentals of GPR and two different acquisition setups for a GPR system are discussed. Basic interpretation tools for travel-time and velocity estimation are described, and finally, case studies are presented, followed by conclusions.