As we’re all too well aware, the threats facing the aviation sector have evolved enormously over the past three decades. Once, an airport security screener’s concerns were limited to traditional guns and knives and rudimentary homemade bombs carried by would-be hijackers. Now, everything from radios and notebook computers to shoes and beverage containers may conceal bombs.
Guns and knives have evolved too. They are now mass-produced in large part from organic polymers—plastic—not just metal. And seven years ago, a handful of hardware store box cutters, probably containing less metal than a typical belt buckle, helped alter the course of history.
Yet in the years immediately following 9-11, airport security checkpoints advanced little from those first fielded in the 1970s—consisting of baggage x-ray machines and magnetometers. That, however, has begun to change.
One new approach, initially called “advanced technology” (AT) baggage screening, has come to be known as “dual view” (DV). The Transportation Security Administration (TSA) began testing the AT/DV machines in 2007. As of this summer, they were deployed to 250 of the 2,000 lanes at 700 TSA-run checkpoints around the country. The agency plans to field an additional 600 by the end of 2008 and another 230 early in 2009.
TSA uses equipment from two companies—Smiths Detection’s HI-SCAN 6040aTiX and Rapiscan’s 620 DV. As the name implies, the dual-view technology gives TSA transportation security officers (TSOs) two views of each bag passing by the x-ray scanner, one horizontally and one diagonally from below.
“What it does is it provides you with more information about the content of the bag, you see overlapping items in the bag from different cross sections,” explains Mark Laustra, a vice president for homeland security with manufacturer Smiths Detection.
Threat detection is the main goal, but maximizing passenger throughput also matters for any screening technology so as not to unduly interrupt the flow of travelers. Peter Kant, Rapiscan’s vice president of global governmental affairs, explains that the dual perspective not only helps identify threats but also helps identify false alerts, which are far more likely to bring about needless secondary visual inspections that slow the checkpoint.
The AT/DV systems rely on traditional “transmission” x-rays that pass through the baggage. Based on the strength and diffraction of waves received by the machines’ sensors—like light through a prism—software helps assess the density and relative atomic weight of a bag’s contents. The system can then determine which substances are inorganic—like metal—or organic, which could include plastic weapons or explosives.
Software is the system’s critical element. It uses algorithms (complicated decision-making equations) to determine how to categorize an item; it then tags items in the bag with a color code for display on the TSO’s monitor.
In the case of the Rapiscan system, organic items—which could include explosives or polymer-based handheld weapons—appear in shades of orange and red, and inorganic in shades of green and blue, with increased darkness indicating higher densities or object overlap.
While TSOs can independently alert on any bag for secondary visual inspection, both the Smiths and Rapiscan systems’ software provide automatic algorithm-based threat detection. If, for example, the Smiths aTiX software spots a suspect substance or object, the machine superimposes a red box and arrow over that area on the monitor to ensure that operators won’t overlook it.
TSA also asked developers of this technology to make it adaptable or malleable so that it will work against unforeseen future threats as they arise. That malleability and scalability resides in the ability to write new algorithms for the software. Currently, both firms are working with the TSA on new algorithms to detect anomalies in laptop computers, and they are also trying to write code that can discern between harmless liquids, like shampoo, and explosives, like acetone peroxide.
If successful, the new software may save travelers from removing liquids and laptops from bags at checkpoints. “[W]e know those are two major pain points for travelers,” says TSA spokeswoman Ellen Howe.
As with prior x-ray machines, the AT/DV machines offer the TSA threat image projection (TIP) capability for training and evaluation. With TIP, simulated threat images that look real to the TSOs are regularly superimposed on real passenger bags as they pass through checkpoint x-ray machines.
When TSOs alert on a simulated TIP threat, the system informs the screener that the image was only a simulation and notes the alert. If the threat is real, the belt stops, and the bag is diverted for secondary screening.
If the screener misses a simulated threat, the omission is recorded. Missed TIP images are reported to the screeners’ supervisors. A TSO may then be assigned additional training or to be asked to take other action.