Ground Penetrating Radar detection of unmarked historic graves at the Fairlawn Cemetery in Stillwater, Oklahoma

Ground Penetrating Radar (GPR) survey was conducted to detect historic unmarked graves from the period of the Civil War (1861–1865) at the Fairlawn Cemetery in Stillwater, Oklahoma. The GPR survey at the Fairlawn Cemetery will help preserve the unmarked historic graves if they exist or clear sections of the cemetery for possible expansion. GPR detection of historic graves are often a challenge as these graves are made of wooden boxes, bones and coffins, with no metal caskets or concrete burial vaults. It was even more challenging to detect unmarked graves in this study as the cemetery is covered with iron-rich silty clay soil, which attenuates the GPR signals. We conducted the GPR survey along a grid consisting of 44 parallel 30-m-long profiles spaced at 50-cm intervals using the 400-MHz antenna. The acquired GPR data were processed as 2D profiles and produced a pseudo-3D GPR volume to resolve the unmarked graves. Multiple features extracted from the pseudo-3D volume at depths ranging from 0.7 to 1.3 m aligned along three north–south rows. Based on the dimensions, orientation, distribution and depth of burial of the anomalous features relative to the recent graves, we interpreted these features as unmarked graves. This study has demonstrated the GPR as an effective non-invasive technique in detecting historical unmarked graves that contain no metal caskets or concrete burial vaults. This work will contribute not only to the science of historical archaeology but also to prehistorical archaeology, as caskets were not typically part of the prehistorical burials, and the modern-day archaeology, particularly in the cases of mass graves in recent conflicts.