Reading Between the Lines: Evaluating GPR Transect Spacing Intervals Employed to Identify Historic Archaeological Features at the William Harris Homestead Site, 9WN168, Walton County, Georgia

Abstract

This thesis examines the variable distance between transect/line spacing when using ground-penetrating radar (GPR) as a method for the identification of historic subsurface features associated with enslaved African American features at the William Harris Homestead site, 9WN168, in Walton County, Georgia. The fieldwork for this thesis sought to identify and interpret nineteenth-century subsurface features associated with the enslaved African American individuals who lived on the homestead utilizing 0.25 meter (m) transect spacing with a single channel 400 MHz antenna. This thesis sought to evaluate whether the collection of transects at 0.25 m intervals compared to wider spacing such at 0.5 m or 1 m intervals not only allows for greater resolution in the data but also whether tighter intervals locate subsurface features not identified at wider intervals. How does GPR interval spacing affect the quality and accuracy of the reflection data collected at an archaeological site using a single channel 400 MHz antenna under similar soil conditions, and does smaller interval transect line spacing support better interpretation of GPR results? The importance of line spacing intervals used for identifying subsurface features at archaeological sites has been emphasized in the literature (Conyers 2012:28; Goodman and Piro 2013:74), however, there have been very few evaluations of the difference of clarity or accuracy that closer interval line spacing provides when compared to wider intervals (Pomfret 2006). The reflection data examined by this thesis were gathered at the William Harris Homestead, a nineteenth-century farmstead in Walton County, Georgia. The GPR investigations sought to identify the burials of the enslaved African American people who worked at the homestead and any features associated with their living quarters. The methods for gathering the GPR reflection data involved testing gridded areas at 0.25 m interval transect spacing. The data were then processed at 0.25 m, 0.5 m, and 1 m intervals to compare resolution and the features identified by the three data sets. The results indicate that while the resolution of the imagery created from the 0.25 m interval spacing is superior to the imagery created at 0.5 m or 1 m intervals, there were no additional potential features identified. Overall, this appears to be correlated to the size of the subsurface features identified, since almost all were found at the widest interval. However, the potential size of some smaller burials and their orientation; along with the size of potential structural features targeted at the site could be determining factors for the utility of 0.25 m interval transect spacing. When evaluating the usefulness of a closer interval GPR transect strategy for single channel 400MHz frequency antennas in cultural resource management, it should be utilized for projects where there are fewer time and budget constraints along with prime environmental conditions.