By Sid Perkins
From Washington, D.C., at a meeting of the American Academy of Forensic Sciences
Aerial surveys that scan the ground at many wavelengths, some visible and some not, may offer a way to quickly and easily detect clandestine mass grave sites.
During field tests in Costa Rica, Margaret Kalacska, a remote-sensing analyst at Simon Fraser University in Burnaby, British Columbia, and her colleagues buried several slaughtered cattle—a weight approximately equal to that of eight adult humans—in a hole 5 meters square and 1.5 m deep. In smaller holes nearby, they buried single carcasses. Yet another hole was filled with nothing but soil.
One month later, team members scanned the sites from a high-flying jet at narrow bands of wavelengths ranging from 400 nanometers (blue light) to 2,500 nm (shortwave infrared radiation). The carcass-containing plots clearly stood out from other areas, especially at some infrared wavelengths, Kalacska says. Ground-based observations indicate that those differences, probably related to subtle chemical changes in the soil over the carcasses and in the vegetation that eventually grows there, persisted throughout the 16-month test.
Kalacska and her colleagues will continue to monitor the faux grave sites to determine how long they remain readily detectable. Similar field tests in other environments will ascertain whether the multiple-wavelength technique could be widely applicable, she adds.
