Multiantenna GPR data acquisition design

Raul Cova, Matthew J. Yedlin, David C. Henley, Jean-Yves Dauvignac, Nicolas Fortino, Christian Pichot, Stephane Gaffet

Detailed characterization of shallow sediments requires the use of very high frequency signals able to resolve fine changes in rock properties. For this reason Ground Penetrating Radar (GPR) has been chosen by the Matter-wave laser Interferometric Gravitation Antenna (MIGA) project to provide the information needed to apply near-surface corrections. Given the similitude of the physics of electromagnetic waves and seismic waves we used seismic modelling software to simulate GPR signals. The goal was to study two acquisition setups designed for the data acquisition. The original setup consisted of eight GPR transceivers, five of them spaced at 0.2m and the rest at 1m, for a maximum offset of 3.8m. This setup, despite providing a regular offset sampling was not able to provide the data needed for accurate velocity picking. For the second design the separation between the first and second group of transceivers was increased from 1m to 4m to provide a maximum offset of 6.8m. This setup provided better data for velocity picking, especially for deep events. However, under this configuration not all offsets could be sampled. The time images obtained confirm that a depth migration is needed to properly map the dip of the interfaces, especially in areas with significant lateral velocity changes. Performance of depth migration and inversion algorithms on the modelled GPR data remains to be explored.