Topographic migration of georadar data: Implications for acquisition and processing

Abstract

Application of conventional elevation static corrections and migration to wavefield data recorded on irregular surfaces may result in poor reconstructions of complex subsurface features. Particulary poor images may be obtained at locations where the depths to target structures are comparable to undulations in the surface topography. For example, topographic relief of only 1-2 m may be important for the processing of georadar data. We describe an algorithm that allows georadar data to be migrated directly from gently to highly irregular acquisition surfaces. When applied to a variety of complicated synthetic data sets, topographically migrated images are observed to be markedly superior to those produced by two standard processing schemes. Extensive tests demonstrate that topographic migration should be considered in regions characterized by surface gradients ≫10% (i.e., dips ≫6°). For effective topographic migration, lateral and vertical coordinates of the georadar antennas should be determined to better than 10% of the dominant georadar wavelength, and velocities should be known to within 10–20% (e.g., 0.01–0.02 m/ns) of their true values. When applied to data collected across a moderately dipping (∼14°) rock glacier in the Swiss Alps, georadar sections resulting from two standard processing schemes have reflectors with depths and dips that differ by a significant 10–15% from those in the topographically migrated images.