Three-dimensional ground-penetrating radar imaging of sedimentary structures, fractures, and archaeological features at submeter resolution

Contemporary geoscientific shallow-subsurface assessment chiefly relies on outcrops, drilling, excavations, and sometimes geophysics. Often the information gathered is insufficient to accurately characterize the archaeological and/or geologic record and ongoing shallow-subsurface processes that affect a variety of economic and environmental aspects of our society. The extra effort of acquiring very dense ground-penetrating radar (GPR) survey grids and three-dimensional (3D) data processing transforms uncorrelatable and uninterpretable GPR signals into clear images of complex shallow-subsurface anatomy with an unprecedented resolution. Here we present two examples of noninvasive 3D shallow-subsurface imaging. Example 1 images decimeter- to meter-scale sedimentary structures in a Pleistocene oolite shoal-barrier bar setting. Example 2 images the fracture network in a Triassic limestone quarry. Denser-than-quarter-wavelength grid acquisition in combination with 3D migration processing focuses scattered energy and removes out-of-plane reflections. In addition to conventional vertical cross sections, horizontal depth slices and data volume animations reveal previously unseen diagnostic patterns of past human activities, laterally changing depositional processes, and fracture networks including near-vertical joints with millimeter apertures.