Detecting weapons of terrorism

He stands less than 2 ft tall, weighs less than 100 lb, doesn't wear a stitch of clothing, barks occasionally, and spends a lot of time with his tongue hanging out. Terrorists beware, though. Chief is one of the most-supersensitive explosives detectors at O'Hare International Airport (Chicago, IL)—and he doesn't work alone.

While the best weapons detectors at key facilities in this nation's infrastructure remain members of the K-9 unit, their backup team increasingly includes an array of supersensitive optoelectronic detection de vices. The reasons are clear—in recent years, criminal bombing incidents in the USA have exceeded 2500 annually. The picture looks bleaker when the tally includes the number of incidents related to other weapons of terrorism from handguns to pathogenic micro-organisms—a small, but growing threat.

Counter-terrorism support for the K-9 team could come in the following forms:

• Portable infrared devices that can spot concealed weapons from across the street
• Computed-tomography equipment that can check luggage for trace amounts of plastics and other explosives.
• A portal that can "smell" trace amounts of explosives, chemicals, and possibly biological weapons on people as they walk through it.

Combined with Chief and his colleagues, these tools will present a formidable first line of defense against terrorism—far superior to the conventional metal detectors currently in use.

According to the National Institute of Justice (NIJ; Washington, DC), the problems with conventional detection systems have been their limited range, emphasis on metal detection, and high rate of false alarms. The December 21, 1988, bombing of Pan Am flight 103 over Lockerbie, Scotland, drove home two facts. The first is that not all weapons have a high metal content. The second is that a relatively small amount of plastic explosives can do tremendous damage.

Detection devices designed to resolve such issues often fall into three categories:

• Passive technology that reads existing natural emissions from objects to spot concealed weapons or explosives
• Active technology that requires artificial irradiation of an individual or item to locate weapons
• A hybrid of such equipment.

Passive detection equipment is exemplified by the millimeter-wave technology currently under evaluation at NIJ's National Law Enforcement and Corrections Technology Center/North east Region (Rome, NY). According to David Ferris, who heads the lab's concealed-weapons detection program, the system will allow rapid and remote detection of metallic and nonmetallic weapons, plastic explosives, and other contraband concealed under multiple layers of clothing at a distance of up to 12 ft. Required equipment includes a fixed-site camera that can be mounted on a cruiser, a monitoring console, and a prototype hand-held camera with a video screen connected by cable to a signal-analyzer box.

Hybrid passive technology under evaluation at the Rome center combines millimeter-wave and infrared cameras in a stand-alone unit and sensor-suite combination. According to Ferris, these techniques complement each other. While the infrared camera has a greater performance range, the millimeter-wave camera has better resolution.

Portals spot hidden agendas

Examples of active technologies include conventional x-ray portals at airport terminals, as well as computed-tomography (CT) equipment from InVision Technologies (Newark, CA). The firm's equipment—based on the same technology as medical CT scanners—is the first of this equipment type approved by the Federal Aviation Administration (Washington, DC) for explosives detection.

Leave a bag unattended in the main terminal, and Chief or one of his four-legged buddies will probably check it out. Check that same bag at one of many international airports, and InVision's equipment will examine it. The system first uses traditional x-ray radiography to determine areas of interest inside containers, such as passenger luggage. A rotating x-ray system then takes profiles at many different angles that a computer combines to create a single cross-sectional digital image for each area of interest. These images, which are independent of surrounding objects, can be compared against stored images of explosives.

Not quite falling into the active detector category is the supersensitive explosives-detection portal under development at Sandia National Laboratories (Livermore, CA). According to Kevin Linker, lead researcher on the project, the detector doesn't image concealed weapons. Instead, it basically shoots puffs of air at people and then sniffs the air to detect any residual concentrations of explosive materials that are blown off a person's skin and clothing. The portal looks like an airport metal detector with vents and nozzles on its inside walls and ceiling. A passenger would stand inside the portal for a few seconds while the detector sends quiet, gentle puffs into the space. The system then collects an air sample and passes it through a chemical sensor called an ion-mobility spectrometer, which recognizes the chemical signatures of a variety of explosives. The equipment can be adapted to support other detection needs such as chemical and biological agents or narcotics.

"Taking one or even several baths won't necessarily protect a person that has recently come into contact with such materials from detection," said Linker. "In tests last year at Albuquerque, NM, international airport, one of some six hundred passengers who volunteered to enter the portal tested positive for explosive materials days after he had last had legitimate contact with such materials."