“We’ll probably never know their names, but at least we’ll know how many are buried here,” says Brad Embry, cemetery supervisor at Oakwood Cemetery in High Point, North Carolina. Here being the cemetery’s historically Black burial section, where scores of unmarked and unaccounted for graves could date back to the cemetery’s beginning in 1859.
“Once we get a number, we’re going to put a permanent number on each burial site so we’ll know that somebody is buried there,” says Embry.
Using ground penetrating radar, New South Associates of Greensboro, North Carolina, is handling the surveying of the land, which includes two large land grids of 3,800 square meters. Early results indicate lots of unaccounted for depressions in the earth, but it is still too soon to tell says assistant geophysical specialist Maeve Herrick. After a survey in June, results are still pending.
“One problem we tend to encounter is vegetation in the survey area. A GPR antenna must couple with the ground surface to obtain high quality readings. When a site contains long grass, underbrush, or fallen trees and logs it can be difficult or impossible for the antenna to achieve good ground coupling,” Herrick explains. “This project was in mowed grass, so data quality was excellent.”
In order to conduct analysis, GSSI antennas, control units, and processing software are all used. “In this case, we used a 350 MHz hyperstacking antenna with an SIR 4000 control unit,” says Herrick. “Frequencies used for archaeological survey are typically between 200 and 1000 MHz. We usually use a 350 MHz or 400 MHz antenna, but sometimes use a 900 MHz or 200 MHz antenna, depending on the site type and local conditions. This would be considered a mid-range frequency.”
Higher frequency antennas provide greater data resolution, but do not penetrate as deep. Lower frequency antennas can penetrate more deeply, but data resolution is not as detailed. Antennas 350-400 MHz for cemetery grounds provide an ideal compromise between penetration and resolution.
"Radar reflections are produced when waves encounter changes below the ground. These changes can be any subsurface feature that is electromagnetically distinct from the surrounding soil matrix," Herrick explains. "With graves, this is typically the grave shaft (bottom or sides), the coffin or casket, void space, or sometimes a layer produced by decompositional fluid. Bodies themselves are very rarely detected. When they are, radar waves typically reflect off a void space produced by a chest cavity. It is impossible to tell from the images produced from the data if these types of reflections have been produced by a body or a void space in a coffin or casket. Caskets typically produce stronger reflections than bodies buried in shrouds, but there are many variables that can affect the strength of reflections produced by each type of interment."
The beauty about in the ground penetrating radar method is that it does not disturb those resting in peace, says Herrick.
"Our work is reproducible, so when better technology exists in the future, someone could go back to a site we have surveyed and compare to our results," she explains. "Other archaeological methods are inherently destructive and unreproducible. Geophysical mapping can also provide a relatively large-scale perspective of a site. Features over great areas can be mapped, leading to broad interpretations of a site or landscape."
About New South Associates
New South Associates, Inc. is a cultural resources management firm that conducts cultural resource studies for clients typically in compliance with federal, state, and local regulations. New South employees specialize in various fields including archaeology, history, architectural history, mortuary studies, and archaeological geophysical survey. The Greensboro branch hosts the geophysics department. Geophysical specialists survey archaeological sites and cemeteries primarily using ground-penetrating radar and magnetic gradiometer.