Modelling GPR reflections from magnetic susceptibility and electrical conductivity variations

Typical GPR sections show a multiplicity of reflection signals, whose origin is usually considered to be related solely to variations in the electrical pennitivity of soil materials. The possibility that some of these reflections could be related to variations in electrical conductivity, is commonly ruled out on the basis of the operating frequency of current GPR instruments. Magnetic susceptibility variations , on the other hand, are commonly neglected because in most situations they affect velocity much less than electrical permitivity . In general, however, neither GPR operate at their optimum frequency nor can magnetic susceptibility be neglected at large. The objective of the presented work is to asses the relative importance of the last two properties in GPR studies. In general, actual field conditions usually fall between two extremes . One is the case of the very conductive ground where GPR is not applicable; the other is a completely transparent medium with perfect reflections. The intermediate cases may include very resistive media but with high enough conductivity contrasts to produce measurable reflections. We test this hypothesis along with the possibility that some of the observed reflections in GPR sections could also be due to natural- magnetic susceptibility variations. We consider a plane-wave source in the presence of a horizontally layered model whose three electromagnetic properties vary from layer to layer. Our results indicate that reflections due to electrical conductivity and magnetic susceptibility variations, can under natural conditions be of the same order as those associated with electrical pennitivity.