It's nowhere near battlefield-ready yet, but it's possible.
It's getting harder and harder to hide these days. Thanks to through-the-wall sensors, such as Camero-Tech's line of Xaver tactical radars, law enforcement and the military can detect anyone inside a closed room and determine his distance from the device. In fact, the FBI and U.S. Marshals Service have been secretly using these sensors for more than two years, according to USA Today.
Now DARPA wants to go one step further: It is researching ways of seeing around corners and behind walls, something not possible with conventional line-of-sight cameras and scopes. Called theRevolutionary Enhancement of Visibility by Exploiting Active Light-fields (REVEAL) program, the idea is to use bouncing photons of light to construct a 3D image of a person otherwise hidden from view.
DARPA didn't respond to a request from PM for an interview with REVEAL program manager Predrag Milojkovic. But DARPA's recent announcement of REVEAL indicates the agency is using as a springboard the pioneering work of Ramesh Raskar, head of the MIT Media Lab, and Andreas Velten, a University of Wisconsin-Madison physicist.
That team, which earned the team a 2012 Breakthrough Award from Popular Mechanics, used a femtolaser to flash a pulse of light lasting less than a trillionth of a second against a flat, vertical surface. The light then scattered off of that surface, and the bouncing photons interacted with an object—in this case a small poseable mannequin—otherwise hidden from the operator's view.
A very high speed camera, sitting alongside the laser, then registered the bouncing photons as they returned at slightly different speeds, explains Ashok Veeraraghavan, a professor of electrical and computer engineering at Rice University who was on the team. This time-of-flight information allowed researchers to tell how far each photon had traveled and what it had bounced against. Ultimately, that helped them construct a crude 3D image of the hidden mannequin.
Clearly, the ability to see around corners would be a huge advantage in war. But it's one thing to conduct round-the-corner imaging under the controlled conditions of a sterile lab, and it's quite another to try it on the battlefield, Veeraraghavan says.
For starters, the equipment you need (at least for now) can take up a whole table, so forget about wearing it like a pair of night vision goggles. Furthermore, the imaging process isn't instantaneous. Before you go bouncing light off of a wall, you need to know the reflectiveness of the surface. It is matted or mirror-like? All that matters to the scattering light. Next, one has to contend with the light measurement and image reconstruction.
"You need to do multiple measurements over a period of many minutes," Veeraraghavan says. "Then there's the 'deconvolution,' to undo the effects of multiple [light] scattering. It takes up to several minutes to solve these computational problems before an image of these unseen objects can be created."
Finally, everything must remain still, including the hidden object. "Currently, minor movements—things like vibration, camera movement and laser movement—effect the quality of the reconstruction," he says.
To put it simply, then, DARPA faces a host of challenges in making this technology ready for the real world. The four-year REVEAL program doesn't aim to develop a deployable system. It's mostly looking at the fundamentals. To build a real round-the-corner imager, sensors would need to be faster and more compact, and scientists would need new techniques to address unpredictable environmental conditions. And that, Veeraraghavan says, is still many years away.
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