Knowing where burials lie is often essential. Churches, cemetery managers, local authorities, archaeologists and contractors all need to understand burial positions within an area before they plan new graves, extend a cemetery, lay services or carry out building work. This article shows how we use processing software to pull grave locations out of ground penetrating radar (GPR) data, using an example from one of our completed surveys.
What the image shows
The image is a 3D rendering produced in GPR-Slice, the software we use to process and visualise GPR data. The rectangular shapes are the positions of graves at different depths, down to a maximum of 2.5 metres below the surface. The linear features are the routes of known utilities crossing the area.
Seeing graves and services together in one view makes it much easier to plan work around both.
How the data was collected
The survey used three UTSI dual-frequency radar units arranged side by side as an array, giving a line spacing of 0.3 metres. Collecting several lines at once in this way covers the ground quickly and gives dense, even coverage. That density matters when the targets are graves, which are relatively small and need closely spaced lines to show their shape.
How the data was processed
We used the 400 MHz data, which gives a good balance between detail and depth for targets of this size. The raw data was passed through a series of filters to remove noise and bring out the reflections from buried features.
The processed data was then iso projected. Iso projection picks out the parts of the data with a high reflective contrast, meaning the places where the radar signal changes most sharply, and draws them as 3D surfaces. In a cemetery, those strong contrasts mostly come from grave cuts, burials and buried services. The result is a 3D view that can be rotated and sliced to show where each target sits and how deep it is.
Why a 3D view helps
A single radargram shows one slice through the ground. A grave may appear as a reflection in one line and be missed in the next. Building the lines into a 3D block, and then into iso surfaces, shows the full shape and orientation of each feature. Rectangular, consistently aligned shapes are typical of graves, which helps separate them from tree roots, rubble and other features.
What the results are used for
The data gives the location and depth of graves and utilities before any further work takes place. That information helps:
- avoid disturbing existing burials when planning new plots
- plan service trenches and foundations around graves
- record burial grounds where plans are missing or incomplete
- guide archaeological evaluation before development
Limits of grave detection
GPR detects graves from the changes they make to the ground, such as the backfilled cut, a coffin or a vault. Results depend on soil conditions. Wet clay reduces depth, and very old graves may leave little contrast with the surrounding soil. GPR cannot confirm that a feature is a burial on its own, so findings are interpreted with the site layout and any records, and should be verified where needed.
Grave surveys
We survey churchyards, cemeteries and burial grounds for clients planning new burials, building work or archaeological evaluation. See our unmarked graves survey page, or contact us to discuss your site.