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Finding bodies buried in unmarked graves can be extremely difficult, but lasers might be able to help.

Lidar uses quick pulses of laser light to make a 3D map of a surface. Katie Corcoran at Oak Ridge National Laboratory in Tennessee and her colleagues used it to measure how the surface of a shallow grave changes over time, in the hopes that it could be used to find the bodies of missing murder victims.

The researchers dug four shallow pits and buried corpses of individuals who had donated their bodies for research in three of the pits, leaving the fourth empty as a control. One grave contained a single body, another contained three and the third contained six.

After the bodies were buried, the researchers filled the pits back in with all of the dirt that had been removed and tamped it down.

They used lidar to scan the area before the bodies were buried, one day after the burial, and then again four months and 21 months later. The first scan revealed that the surface of the graves became elevated by a few centimetres shortly after burial. It then shrank back down again between the second and third scans.

The decrease in elevation was likely caused by the bodies decomposing聽in the first few months, creating more room for the soil to settle, the researchers say. The bodies in the largest grave were all placed at one end, which sank more than the side filled with only dirt.

The results show that investigators could narrow down possible grave site locations in the months after the grave is dug by carrying out two or more lidar scans, which can be done from the ground or even an aircraft, Corcoran says. 鈥淎fter a lidar survey is completed and possible grave locations identified, it would then be up to investigators to explore those locations in person.鈥�

This could make it easier to find graves that are in difficult to reach areas or have been camouflaged. 鈥淧iling leaves, or employing some other type of camouflage, will not trick lidar the same way it might trick the human eye,鈥� says Corcoran.