麻豆传媒

Drones聽could soon help search for murder victims in remote areas. In recent tests, drones equipped with laser scanners identified graves in Australian bushland. Now, the nation鈥檚 police聽want to use the technology in an ongoing case.

In the investigation, the police suspect that a missing person is buried in a densely forested area. However, all searches so far have come up empty. By using drones carrying a scanning technology called lidar, they hope to cover a larger area more quickly than they would be able to on foot.

Lidar works by pointing lasers at a target and measuring how much time it takes signals to be reflected back. The laser pulses bounce off the surfaces, such as leaves, they encounter. In this instance, they travel through gaps in the forest canopy to offer a view of the聽trees as well as anything buried in the soil below them.

To test the technique, Soren Blau at the Victorian Institute of Forensic Medicine in Melbourne and her colleagues buried bodies donated for research purposes in聽a 20,000-square-metre area of聽dense forest.

The cadavers were put in three聽types of grave to simulate different crime sites: one containing only one body, another with three and a larger grave with six bodies. Three empty graves were dug as controls.

Patrick Weeden at drone company Scout Aerial then flew lidar-equipped drones over the target area. He didn鈥檛 know any details about the burials.

Weeden used an algorithm to digitally remove the vegetation from the resulting images and reveal the ground beneath. This allowed him to spot聽changes both on the surface and underground, letting him successfully identify five of the six graves.

However, the technique failed to spot the grave containing the single body, so the process still requires refinement.

Lidar only picks up soil disturbances, so one limitation of聽the technique is that there is no easy way to distinguish the graves of human bodies from those of animals, or even changes to the ground due to other causes.

But the technique could still prove valuable. Searching an area聽requires a lot of resources, particularly when investigators don鈥檛 know exactly where they should look. The lidar-carrying drones can narrow down a huge search area containing difficult terrain to a few places of interest.

鈥淒rones have a capability of rapidly pinpointing areas for subsequent investigations,鈥� says Jamie Pringle at Keele University in the UK.

For the moment, the technology is expensive: Weeden says that a lidar unit costs A$60,000 to A$200,000.

Elsewhere, researchers are testing cheaper methods. Peter Masters at Cranfield University in聽the UK recently fitted out a consumer drone with a GoPro video camera and a relatively cheap lens attachment that filters near-infrared light to produce images showing soil disturbance. He used it to locate bodies buried in a natural cemetery.

But this method only works well for open areas without tree cover, as it can鈥檛 map the ground beneath vegetation.

Eventually, lidar could be used聽to proactively search vast areas and automatically detect if聽anything looks suspicious. It聽could also be put to other uses than simply helping a police force聽locate a single or a small mass grave, says Weeden.

As well as generating new leads for cold cases, he believes it could also help uncover mass graves in conflict areas as evidence of war crimes or genocides.