FREQUENTLY ASKED QUESTIONS
Find out more about geophysics
How does locating unmarked graves (UMGs) with GPR work?
Graves older than the mid-twentieth century typically consist of an excavation with a wooden casket or shroud burial. Over time, the organics decay leaving low-density backfill in the grave shaft surrounded by undisturbed high-density residual soils. This contrast produces radar reflections around the perimeter and off the base of the grave shaft and low resistivity readings in the backfilled soil.
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Learn more about how GPR works by reading about a past project...
How effective is GPR?
The efficasy of GPR depends on a few factors: the feature of interest's depth, soil moisture conditions, soil type, etc.
In optimal conditions, the GPR is accurate enough to locate the edges of individual burials. In the past, grave locations from a 19th-century cemetery were verified with plow zone stripping before moving the cemetery to construct a new high school.
How does electrical resistivity detect unmarked burials?
Electrical resistivity (ER) measures the resistance of electrons flowing through the subsurface. An electrical current is induced between two outer electrodes and the resistance to the flow of electrons is measured with the two inner probes.
Rainwater infiltrates much quicker into the loose soil backfill of a grave shaft than the surrounding undisturbed soils. As a result, the soil in a grave shaft has a higher moisture content. Soil with a higher water content has a lower electrical resistivity. Areas with a lower resistivity can be indicative of an unmarked grave. Seramur & Associates uses electrical resistivity to map unmarked graves and ground truth GPR anomalies.