Acquisition and processing strategies for 3D georadar surveying a region characterized by rugged topography

Efficiently performing 3D ground-penetrating radar (GPR or georadar) surveys across rugged terrain and then processing the resultant data are challenging tasks. Conventional approaches using unconnected GPR and topographic surveying equipment are excessively time consuming for such environments, and special migration schemes may be required to produce meaningful images. We have collected GPR data across an unstable craggy mountain slope in the Swiss Alps using a novel acquisition system that records GPR and coincident coordinate information simultaneously. Undulating topography (dips of 8° to 16°) and boulders with diameters up to about 2 m complicated the field campaign. After standard processing, the data were found to be plagued by time shifts associated with minor coordinate inaccuracies, uneven antenna-ground coupling, and numerous small gaps in data coverage. These problems were resolved by passing the data sequentially through an adaptive f - xy deconvolution routine and f -k_x and f -k_y filters. This filtering also reduced incoherent noise. Finally, the data were migrated using a 3D algorithm that accounted for the undulating topography. The nonmigrated and migrated images contained gently and moderately dipping reflections from lithological boundaries and actively opening fracture zones. A suite of prominent diffraction patterns was generated at a steeply dipping fracture zone that projected to the surface. Through this case history we introduce a general strategy for 3D GPR studies of topographically rugged land.