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Scanning Crowds for Bombs

THE AIRPORT CHECKPOINT is a linchpin of aviation security, but one of its unintended consequences imparts vulnerability: the long, weaving line of travelers who await screening. The lines present suicide bombers with a potential target that is common not only to airports but also to public events where masses must pass through security screening.

Passive millimeter wave scanners can spot suspicious objects under clothes, and someday, laser spectrometers may spot explosive residue on clothing yards away. Both technologies still, however, would require that people pass through choke points, as these technologies can only scan one person at a time.

With these threats in mind, the Air Force Research Laboratory (AFRL) at Wright-Patterson Air Force Base, Ohio, pitted students from rival colleges against one another in a competition to see which school could better detect simple improvised explosive devices (IEDs) across large areas and groups.

The winning entry, fielded by students from the University of Michigan, relied on sensors linked by a wireless network, with software that processed data from the sensors to spot potential threats. The concept holds the promise of scanning large areas and crowds for explosive threats.

The AFRL based the competition’s scenario in part on an historical event—the 1996 Olympic Park bombing in Atlanta, where Eric Rudolph detonated a fairly rudimentary IED—a pipe bomb composed primarily of metal.

Teams from Michigan and arch rival The Ohio State University were challenged to detect similar threats as they passed through a 100-square-foot area packed with vehicles and volunteers that re-created a pregame tailgate party.

Knowing the threat objects would likely contain large amounts of conductive metals, the Michigan team mounted their own homemade magnetometers atop skinny traffic cones and arranged them around the perimeter of the competition area. These devices transmitted data back to a notebook computer, which used the team’s software to analyze the data and project potential threat objects onto a top-view rendering of the area.

Ohio State developed a “system of systems” that included a magnetometer, an infrared camera, and a radar system that, when coupled with an electromagnet, could detect large metal objects. But, software woes plagued the radar, and Ohio State only detected one of six bombs, compared to four of six detected by Michigan.

Michigan team member Ashwin Lalendran notes that magnetometers alone may not catch explosives that contain little or no conductive metal. The persistent limitations of spectroscopy and millimeter wave, however, have led even the government’s top researchers to reexamine magnetometers for wide-area explosives detection, says Nick Lombardo, project manager with Pacific Northwest National

Laboratory’s Initiative for Explosives Detection.

Lalendran sees the greatest value in Michigan’s software system. As commercial devices used to detect traces of hazardous materials, explosives, biological agents, and radioactivity grow smaller, cheaper, and more sensitive, they might be incorporated into networked sensors that could scan wide areas for threats. The Air Force agrees, and hired Lalendran to continue his work at AFRL.

The challenge was one of four the Air Force is holding this year. The laboratory pits interscholastic rivals against one another and gives competitors a tight deadline and a limited budget to create a pressure cooker, says David Shahady, the lead of AFRL’s Innovation Program.

“If you take a fairly serious problem and give it to these students, they’re young, energetic, and creative. And you create an environment where there’s not much time and there’s competition, you find that they come up with these great solutions,” Shahady says.