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FORT COLLINS, CO, USA, AUGUST 1 2014: Radio controlled DJI Phantom quadcopter drone taking off from a grass field. (Photo: marekuliasz / Shutterstock.com)

Drones and near-infrared photography have become inexpensive technology that is widely available in the 21st century.

Its forensic promise in locating clandestine graves, however, still has limitations in 2018, according to a recent study in the journal Forensic Science International.

Rain and wind, the concealing growth of vegetation over dig sites, and camera limitations on the most common tools mean that GPS surveys and actual ground searches by foot are still superior, according to the study, conducted by Rykker Evers and Peters Masters of the Cranfield Forensic Institute.

“By implementing an (unmanned aerial vehicle) with a low-cost unmodified GoPro camera for visual and (near-infrared) imaging, the ability to detect graves based on the different reflectance characteristics is available,” they write. “However, taking the inexpensive approach by using unmodified cameras with fixed automatic light exposure setting and a lens distortion ‘fisheye’ effect has its disadvantages which are characteristic of the distorted images acquired with the adaption of the NIR filter.”

The tools they selected to test the capabilities were low-cost. The DJI Phantom 1 model, paired with the Go Pro Hero 3, was brought to the natural burial ground called the Westmill Woodland Burial Ground at the Oxfordshire/Wiltshire border. No headstones, embalming, non-biodegradable coffins or other traditional cemetery trappings are found at the site. Live humans only make appearances during funerals and maintenance routines. A total of 138 bodies had been buried in single graves at the site between 2000 and 2017.

Fifty-five of the graves were detected by visual cues, including digging boundaries and vegetation differences.

But then the researchers took to the skies with the small drone. Two flights were made, each lasting about 10 minutes, which produced images every two seconds. The altitude varied between 10 meters and 40 meters.

Many proved unusable, due to blurring from the flight motion, they write.

The pictures that were usable were analyzed using image processing filters, and corrections using algorithms. The images were converted to grayscale to show near-infrared contrast, complemented with Gaussian blurring, the researchers write. A binary image of 0s (black) and 1s (white) were assessed for showing abrupt changes in the soil. 

The NIR showed graves that were not as overgrown. But the traditional imaging and follow-up—by foot—appeared to remain more accurate.

“In general, the method of identification used for the GPS surveying conducting a detailed foot-search appeared to be the most successful method in locating the graves, which is characteristic of the limitation of aerial photography and why more conventional approaches are still generally used,” they conclude.

The promise remains, with better tools, add Evers and Masters.

“Locating clandestine graves through UAV aerial photography techniques may be a very useful method and can be further explored by implementing higher-grade camera technologies for the improved acquisition and quality of images as well as greater capabilities for further processing techniques,” the investigators write.

Aerial surveys have been a great hope of forensic science, from the use of LIDAR in Holocaust archaeology to the use of GPS and precise coordinates. But despite providing clues from altitude, investigators still need to consider the motivation and opportunity of killers to hide the evidence in a race against the clock, as an Italian team proposed in a new searching system last November.

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