Sandberg can undertake Ground Penetrating Radar (GPR) surveys for the detection of graves and cemetery surveys. Due to the sensitivity of these areas, a non-intrusive survey method such as GPR is ideal. A GPR survey team can cover a large area in a single day making it very cost effective survey technique.
Some cemeteries are hundreds of years old; unmarked graves can be common. Likewise misplaced or poorly positioned headstones or markers further complicate matters. Often records are vague or incomplete and there may be serious doubt about the precise extent of a cemetery. Parts may have even been asphalted over.
Detection of graves can be challenging. There is often no surface expression of the burial location. Due to the sensitivity of these sites, the challenge is to explore the subsurface without disturbing the soil.
The Ground Penetrating Radar Survey
The most effective technique is to survey the required area on a regular orthogonal grid with scan lines at 0.5-1m centres. A SIR-3000 GPR control unit would typically be used with a 270MHz or 400MHz antenna. GPR works best in sandy soils which do not contain boulders, stones or tree roots.
A grave is a relatively well defined target, the size is typically 0.5m x 2m and it is typically within 2m of the surface. GPR may detect a number features to help identify a grave, including:
- The coffin (wood, metal, lead lined, etc) or vault
- Disturbed ground structure and excavation features
- Movement or voids caused by collapse of the coffin
The GPR data is saved electronically and processed off-site. Sandberg use GSSI Radan software to process and analyse the data. If appropriate the data can be used to generate 3D models; these are then viewed as a series of depth slices.
The position of detected graves can be plotted on CAD drawings providing the client with clear, easy to understand results.