FirstArrival Traveltimes Inversion Based on Minimal Number of Parameters in shallow crosswell GPR Tomography

Ground-penetrating radar is often used for the characterization of subsurface properties. In this paper, we present a cross-well tomographic inversion algorithm of first-arrival traveltimes which uses only a limited number of parameters. This methodology has been developed for media with significant contrast of electrical permittivity, for example for near-surface sedimentary media. The aim is to determine the distribution of the electromagnetic wave velocity between two wells. We consider that the media can be decomposed into several homogeneous layers, with horizontal or gently dipping interfaces. It is described by a vector of parameters which includes one velocity and one or two thicknesses per layer. This methodology allows to obtain a 1D velocity profile of the medium between the two wells. This inversion scheme was tested on synthetic data. The head waves which appear due to the velocity contrasts are taken account in the inversion. Our inversion methodology was also tested on real data and the obtained velocity models were compared to those obtained using surface acquisition data only. Our results show that the velocity profiles issued from cross-well and surface acquisition appear to be very similar.