Ground Penetrating Radar (GPR) has grown in popularity in usage on cemeteries and on archeological sites (Conyers and Goodman, 1997:11). GPR involves the observation of the reflected component of transmitted electromagnetic waves into the subsurface. The reflections, unlike that of acoustical waves, occur at the interfaces of materials of differing electrical conductivity or permittivity. The depth of penetration for radar waves is frequency dependent and the attenuation of the radar wave in the ground is rather quick compared to that of seismic – a few meters compared to kilometers. Since many, if not most, buried features of archeological interest are not deeply buried; the GPR has utility in the search and characterization of these features. GPR is characterized as a WYSIWIG technique (i.e. what you see is what you get).
The GPR output is a series of radar wavelet traces or scans produced on a chart recorder or computer screen as an antenna is pulled across the ground surface. The radar wave perturbations can directly yield reflection depth and the relative strength of the reflections, such that the form and location of a buried object or feature can be ascertained rather readily. If the velocity of the radar waves can be determined, then the conversion of travel-time between the transmitter and receiver of the reflected wave, can be converted to distance, similar to that which is done in seismic studies. Indeed, the phenomenal advance of the high-resolution post-processing software, GPR_Slice, allows us to tease out the finest details as to stratigraphy and shape of subsurface reflectors or features in plan view, rather than the previous methods of solely vertical readings.
GPR is not X-ray. For cemeteries, one will not see remains in the ground. Instead, grave pits, grave excavation edges, and remnants of caskets if any, will be imaged. Interpretations about the presence of absence of human burials are drawn from the GPR imagery.