Estimation of water content and porosity using combined radar and geoelectrical measurements

摘要

A primary objective in hydrogeological investigations is to obtain information on the water content and porosity of formations. These parameters can be directly related to resistivity. Hence a reliable estimation of these hydrogeological parameters requires that the resistivity (or its inverse, conductivity) should be measured and mapped accurately. By combining different geophysical measurements and information about the geometric structure of the subsurface, the ambiguity of geoelectric inversion for deriving true resistivities can be reduced. Ground penetrating radar (GPR) offers an additional method for inferring the geometric structure and also the spatial distribution of the physical variable associated with water content, namely the dielectric constant. A combination of geoelectrics and GPR allows a more precise description of the subsurface. This is demonstrated by using measurements from a test site in Spandau/Berlin, Germany, where some borehole data exists and the geology is fairly well known. Common mixing formulas were combined in order to derive water content and porosity from the resistivity and dielectric constant. An estimation of hydrogeological parameters based on one measurement alone could not provide the level of confidence and accuracy required for interpretation. By combining GPR and geoelectrics, however, reliable estimates of water content and porosity were obtained which were consistent with the known geological model.