Use of Ground Penetrating Radar to Map Subsurface Moisture Variations in an Urban Area

The range of Ground Penetrating Radar (GPR) applications is very wide and diverse. GPR provides high-resolution continuos profiles, and has been used in various fields (environmental problems, geology, geotechnical engineering, archaeology etc.). This paper describes a test application of GPR in an urban area (Mesagne, Apulia, Italy) for the detection of underground water pipes and to obtain a map of the moisture in the ground around them. Some authors have proven that GPR can be used effectively, although only as a reconnaissance tool, for studies of moisture in the subsurface. Electromagnetic wave velocity in the subsurface depends on moisture via the dielectric properties of the wet material. The free volumetric water content can be determined from the dielectric constant of subsurface terrain by an empirical relation proposed by Topp et al. (1980). GPR wave velocity determination can be carried out by means of several methods. In this paper the hyperbolic anomalies caused by small inhomogeneities and underground water pipes have been considered. The velocity analysis permitted a qualitative estimation of the volumetric water content near the pipe network and the location of possible leaks.