Can GPR Determine the Exact Size of a Subsurface Void Cavity?
Ground-Penetrating Radar can reliably reveal the presence and general boundaries of a buried void, but its reflections blur at depth. GPR therefore estimates a cavity’s width and depth within a tolerance—often a few inches—rather than providing an architect-grade “exact” measurement for most cemetery-mapping projects today.
Ground-Penetrating Radar (GPR) sends high-frequency radio waves into the ground and records the echoes. A void—whether an underground chamber, abandoned utility vault, or the airspace above a collapsed burial—creates a strong, hyperbolic reflection that stands out on the radargram. By collecting parallel survey lines and processing them into 3-D slices, technicians can outline the lateral footprint and estimate the roof and floor of the cavity. Within a cemetery mapping project, this ground penetrating radar cemetery survey is correlated with precise GPS for burial plot mapping.
Signal wavelength, soil conductivity, moisture, and void depth all smear the reflection, so the interpreted edges usually carry a ±2 to 6-inch margin of error. Very shallow, dry, sandy soils yield the sharpest images; deep clay soils can stretch the error band to a foot or more. In practice, GPR delivers a dependable “box” around the anomaly.
For cemetery managers, Sentry Mapping uses ultra-high-frequency antennas to capture the clearest possible view of underground disturbances. The same workflow that distinguishes intact graves from empty plots also flags subsurface hazards, helping you avoid collapses during maintenance or future burials. Learn more in our Complete Guide to Ground Penetrating Radar.