Modeling of cross-borehole radar data in layered media for environmental applications

Synthetic cross-borehole radar records have been computed to examine the feasibility of delineating subsurface layers and zones of hydrocarbon contamination. The radar transmitter and receiver are vertical electric dipoles in boreholes separated by 20 m in a simple layered earth model. Results for a low velocity layer show an increase in arrival time as the layer thickness increases as predicted by mode theory. With both transmitter and receiver in a high velocity layer that is thin compared to a wavelength the arrival time reflects the lower velocity of the material outside the layer. As the layer gets thicker the authors start to get an arrival corresponding to the velocity of the layer. For a range of layer thicknesses on the order of the wavelength both arrivals are seen. In this paper results are given to compare a case with an oil saturated sand layer on the top of the water table to a case without the oil saturated sand layer. A method is demonstrated for detecting the presence of a thin oil layer. Finally an example of tomographic inversion of synthetic data is discussed