3D GPR imaging of shallow plastic pipes, tree roots, and small objects

Abstract

Obtaining high quality and easy to interpret horizontal slices of the shallow subsurface depends on how a 3D ground penetrating radar (GPR) survey is acquired and processed. A field site containing three basic target geometries of linear pipes, curvilinear roots, and small objects serves as a testbed. High-density 250 and 500 MHz single channel GPR surveys covering 250m2 were acquired to evaluate 3D GPR imaging parameters. The results show: 1) a uniform trace density of a quarter wavelength is necessary to image all three target geometries; 2) positioning precision has to be better than half the trace spacing to avoid horizontal jitter; 3) 500 MHz offers a good compromise between dense trace spacing and image resolution; and 4) 3D migration processing focuses diffractions in exact target locations. Sparse 3D GPR only images linear targets parallel to the antenna polarization. Curvilinear and point targets are missed. The findings also apply to multichannel array systems for high quality and efficient 3D GPR imaging of large field sites.