Topographic migration of GPR data with variable velocities

The topographic relief of a typical ground-penetrating radar (GPR) survey can easily be in the range of the target depth. In complex subsurface settings, this requires the application of topographic migration schemes to reliably image subsurface structures. Furthermore, a shallow ground water layer introduces significant vertical variations in GPR propagation velocity, which should be considered during migration to accurately image subsurface structures. In this paper, we present a modified topographic migration scheme, which is able to account for vertical variable velocities by using the root-mean-square (rms) velocity approximation. We evaluate our migration scheme by using synthetic and field data, which represent typical near-surface sedimentary structures often investigated using GPR. These examples demonstrate that a significant improvement in structural imaging quality is achieved by considering rms velocities during topographic migration.