Full-resolution 3D GPR imaging

TLDR

Noninvasive 3D GPR imaging with submeter resolution in all directions reveals the internal architecture of the shallow subsurface, requiring at least quarter‑wavelength spatial sampling. Full‑resolution imaging is achieved by unaliased recording of reflections and diffractions coupled with 3D migration processing, as demonstrated by a 100‑MHz survey with 0.1 m × 0.2 m trace spacing at a fractured limestone quarry. The survey resolved fractures in four orientations down to 20 m, and showed that halving the spatial sampling or using only 2D migration obscures most fractures; the high‑resolution data provide submeter detail of fractured rock, sedimentary structures, and archaeological remains, making full‑resolution 3D GPR a valuable tool for shallow‑subsurface studies.

Abstract

Noninvasive 3D ground-penetrating radar (GPR) imaging with submeter resolution in all directions delineates the internal architecture and processes of the shallow subsurface. Full-resolution imaging requires unaliased recording of reflections and diffractions coupled with 3D migration processing. The GPR practitioner can easily determine necessary acquisition trace spacing on a frequency-wavenumber (f-k) plot of a representative 2D GPR test profile. Quarter-wavelength spatial sampling is a minimum requirement for full-resolution GPR recording. An intensely fractured limestone quarry serves as a test site for a 100-MHz 3D GPR survey with 0.1 m × 0.2 m trace spacing. This example clearly defines the geometry of fractures in four different orientations, including vertical dips to a depth of 20 m. Decimation to commonly used half-wavelength spatial sampling or only 2D migration processing makes most fractures invisible. The extra data-acquisition effort results in image volumes with submeter resolution, both in the vertical and horizontal directions. Such 3D data sets accurately image fractured rock, sedimentary structures, and archeological remains in previously unseen detail. This makes full-resolution 3D GPR imaging a valuable tool for integrated studies of the shallow subsurface.