Imaging Over Sites with Topography and Vector Imaging

Abstract

Correcting the GPR dataset for topography is often necessary to properly image and detect the subsurface structures beneath a site. For instance, archaeological sites that were once built on level ground but have since been subject to variable deposition and thus have variable surface topography, may need to have time/depth slice images created at level elevation across the data to properly reveal the subsurface structures. Goodman et al. (1995) made level plane depth slices across the Spiro House mound sites in Oklahoma. The level plane slices revealed square pithouse floor foundations from Native American Indians which only show up on (horizontal) slices made from topography adjusted radargrams. Standard topographic adjustments to the GPR involve assuming a velocity model for the radargrams, and then shifting the scans vertically to account for the change in topography (Tanaka et al. 2009). Some problems with this method, such as the “peeling effect” caused by differential slicing across the strong ground wave reflection can occur. An effective method to completely remove the peeling effect without having to apply drastic measures such as background filtering to remove the groundwave is possible. The method involves generating a volume from time slices that are independently normalized at each level and then graphically warping these volumes into their topography. Topographically adjusted volumes can then be sliced level plane without any influence of strong ground wave reflection. The details of this method are presented in the section on Level Plane Time Slices in this chapter.