Killer drones that can see through walls.

Science, technology, and life.
Sept. 17 2008 11:49 AM

Nowhere To Hide

Killer drones that can see through walls.

UAV heads up display. Click image to expand.
Display from an unmanned aerial vehicle

For the last couple of days, in the Human Nature blog, I've been looking into a breakthrough cryptically reported in Iraq and Afghanistan: the ability of U.S. unmanned aerial vehicles to identify and track human targets "even when they are inside buildings." Several recently reported technologies might account for it, but Slate reader fozzy suggests looking for the answer in a military research field called STTW, usually translated as "sense-through-the-wall." Has this ability been extended to a distance that allows it to be used by aerial drones?

William Saletan William Saletan

Will Saletan writes about politics, science, technology, and other stuff for Slate. He’s the author of Bearing Right.

Fozzy cites a March 2008 Army technical report on the latest progress in STTW radar methods. (Warning: Most of the documents I'm linking to here are PDFs, and some take a long time to open.) With a few more clicks, I pulled up an April 2008 report from the same research team. Both reports focus on "detecting and identifying humans enclosed in building structures." "Through-the-wall sensing is currently a topic of great interest to defense agencies both in the U.S. and abroad," says the April report. "The U.S. Army Research Laboratory (ARL) has been active in all these fields of investigation, approaching these issues both through hardware design and radar measurements and through computer simulation of various STTW scenarios."


STTW has been around for a while. A 2006 report from the National Defense University mentions a DARPA system that can "detect the presence of personnel within rooms (stated to be successful through 12 inches of concrete)," as well as a commercially developed system with a "30-foot standoff capability." The next step, to protect U.S. personnel, is to put the technology on "unattended" mobile devices. Since the initial context is urban warfare, the pioneering client is the Army, and the introductory platform is unmanned ground vehicles. But the goal is to increase "standoff distance" and spread the technology to other platforms.

Meanwhile, up in the air, drone designers have been struggling with a similar problem: seeing through "darkness, bad weather, and tree canopies." The crucial contribution drones have made in Iraq—providing instant, on-demand customized video to ground forces—doesn't work where the drones' cameras can't see. So American engineers are developing radar that penetrates outdoor obstacles.

What seems to be happening is that these two projects—STTW and UAVs—are converging. In other words, unmanned vehicles that can see through walls. In some planning documents, the merger is explicit. A 2006 "Operational Needs Statement" from the military's Joint Urban Operations Office calls for a "STTW sensor mountable on both manned and unmanned vehicles," including "UAV platforms." A Navy bulletin calls for the same thing.

Conceptually, the merger serves every tactical objective. It increases standoff distance and mobility. It makes aerial drones useful in bad weather and urban settings. It also integrates them into a more ambitious plan: to see the enemy through every wall, not just one. A 2005 DARPA report, for example, proposes to "image through multiple walls and even penetrate whole buildings using distributed sensors on or around buildings," with UAVs assisting ground forces. A 2007 Army Research Lab study explores the ability of ground sensors, working with UAVs, to capture "images from different angles," thereby providing "intelligence on the configuration, content, and human presence inside enclosed areas (buildings)."

Three years ago, according to a defense contractor, the goal was to extend STTW capability to "distances in excess of 100 m," which would start to bring UAVs into the game. Boeing was in discussions to put STTW radar into a UAV. The Army was seeking "a suitable lightweight and compact imaging sensor to be hosted by the Camcopter-small UAV, capable of lifting 65 lbs of payload." The requirement for true aerial mobility was to make the system "lightweight (less than 30 lbs) and portable (less than 4 cubic feet)."

That sounds a lot like the mystery devices now being placed aboard drones in Iraq and Afghanistan. As the Los Angeles Times describes them, "The devices are roughly the size of an automobile battery, but are heavy enough that outfitted Predators in some cases carry only one Hellfire missile instead of two." The effect of these devices, according to a former U.S. military official interviewed by the Times, is that insurgents, even indoors, "are living with a red dot on their head."

Cool, huh? Except that if their walls are now transparent, so are yours. As fozzy astutely asks: "What happens when the government 'brings this technology home'?" And do you think our government is the only one merging STTW with UAVs? Heck, even the Canadians are well into it. "We will put the UWB radar on mobile platforms such as robots or unmanned airborne vehicle," says a 2002 report from Defence R&D Canada. "We are confident that a through-the-roof surveillance capability could be implemented using UWB radars installed on helicopters or small UAV."

Congratulations. The good news is, we might win in Iraq and Afghanistan after all. The bad news is, now we all have red dots on our heads.



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