With quadcopters and other commercial drones becoming cheaper, more sophisticated, and numerous, the US military recognizes the potential security threat these tiny aircraft pose. In order to stay abreast of what drones are where, particularly in urban environments, DARPA has begun the Aerial Dragnet project to develop a system for detecting and tracking small Unmanned Aerial Vehicles (UAVs) at low altitude.

Everyday, thousands of commercial and military aircraft fill the skies. Despite the occasional headline-grabbing accident, aviation's safety record is admirable. According to the US National Safety Council, the odds of dying in an air accident is 1 in 7,178 compared to a motor car's 1 in 98.

Part of the reason for this is that airplanes are not just individual flying machines, but units in a comprehensive air transportation system watched over by various national and international air traffic control systems. These control systems keep an eye on hundreds of thousands conventional aircraft on a daily basis with such precision that when one does literally vanish off the radar, it's big news.

Unfortunately, no such system exists for the growing number of increasingly sophisticated UAVs that are taking to the skies. These have already led to invasions of privacy, near tragedies and have been giving pilots increasing anxiety as many are sighted near airports. But the US military is especially worried that UAVs will soon become a security threat to armed forces in urban settings overseas and a way to comprehensively track large numbers of UAVs of similar size traveling at similar speeds needs to be found.

To address this, DARPA started Aerial Dragnet, which is tasked with detecting and tracking drones flying below 1,000 ft (300 m) in urban settings. According to the agency, this will require new technologies as well as a study of existing systems. However, if it succeeds, Aerial Dragnet will not only help with troop protection, but could ultimately also find civilian applications protecting metropolitan areas in the US from terrorist threats.

Current attempts at developing an urban UAV tracking system are based on tracking systems designed to monitor drones in open areas using large line-of-sight buffers, but DARPA says that these are impractical in cities. What Aerial Dragnet plans to do is exploit the physics of slow, low-flying UAVs in urban settings to track them without the need of a clear line of sight.

The initial idea is to monitor neighborhood-sized areas using something like a tethered or long endurance UAV equipped with sensors to keep watch from above obstructions. Several of these would act as surveillance nodes to track drone traffic through what the agency calls a continually updated Common Operational Picture (COP) of the airspace, which would be available to authorized users through secure data links.

DARPA says that the project will focus on the use of low-cost UAVs and sensor technology combined with off-the-shelf software-defined signal processing to develop a system that is not only inexpensive, but scalable and easily upgraded as technology advances.

"Commercial websites currently exist that display in real time the tracks of relatively high and fast aircraft — from small general aviation planes to large airliners — all overlaid on geographical maps as they fly around the country and the world," says Jeff Krolik, DARPA program manager. "We want a similar capability for identifying and tracking slower, low-flying unmanned aerial systems, particularly in urban environments."

DARPA is looking for teams with expertise in sensors, signal processing, and networked autonomy and have issued a Broad Agency Announcement (BAA) detailing requirements and how to register for a Proposers Day to be held on September 26 in Arlington, Virginia.

Source: DARPA