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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.

Carry-On Baggage

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.

Checked Baggage

Explosives detection systems (EDS) are large, belt-fed machines used to scan unopened checked luggage, in which explosives pose the only critical onboard risk. Drawing on technology adapted from medicine, EDSs are basically computed tomography (CT) x-ray machines, which, like the new AT/DV x-ray machines, use software to interpret data from multiple x-ray diodes.

These machines, most manufactured by either L-3 or GE Security, have a tube-shaped gantry consisting of a massive lead sheath enclosing a spiral array of 11 x-ray diodes. The tube rotates around the bags as they ride a conveyor belt through the machine. The machine’s software interprets transmitted x-rays to generate a detailed, three-dimensional image of the bag and its contents, including identification of potential explosives.

Some forms of EDS have been around for a decade or more, but the technology continues to advance. For example, the throughput of traditional EDS machines is roughly 300 bags per hour. Rapiscan, however, plans to field a technology that can work four times faster, called the Real Time Tomography (RTT) system, Kant says.

Rather than a rotating gantry with 11 diodes, the RTT systems rely on 400 stationary diodes performing the same function, providing 1,000 to 1,200 data points for software analysis in a single instant. The vastly increased amount of data will aid in detection, while the instantaneous scan would speed the process.

The added speed of the RTT system would require multiple screeners to review baggage images if the machines are to provide their maximum throughput. Kant, however, says that one RTT machine would replace several traditional EDS machines.

Passengers

Passenger screening is also evolving to keep up with changing threats. Threats now include not only guns, knives, and plastic explosives but also liquid explosives, radioactive materials, and pathogens. These threats have increased the need to move beyond the traditional metal detector, but that creates special challenges because humans cannot be subjected to the same x-rays as baggage.

Full-body imaging. One way that this challenge is being met is with the full-body scan systems, which use backscatter x-ray or millimeter wave technology. These generate much lower levels of radiation (less than 10 microREM versus 100 milliREM allowed per year). While they rely on different bands of the electromagnetic spectrum, backscatter and millimeter wave machines operate on the same principle. Like radar or sonar, the machines project energy onto an object, and the software interprets what is reflected back.

Generally, the waves penetrate clothing unaffected, are absorbed by hard objects like guns or explosives, and are “scattered,” or reflected back to varying degrees by organic material, including flesh.

A backscatter machine is about the size and shape of a vending machine; the subject gets scanned twice—once while standing facing the machine, then again while facing away from it. The millimeter wave machines that TSA has purchased, manufactured by L-3 Communications, are hexagonal booths with dual sensors that simultaneously sweep across a subject’s front and posterior. They produce a photo negative-like image of a bare body with inorganic threats in black.

The technology works, but it has run into opposition based on privacy concerns. The American Civil Liberties Union has dubbed the machines a “virtual strip search” and “an assault on the essential dignity of passengers that citizens in a free nation should not have to tolerate.”

TSA defends the technology. The agency notes that it is far less invasive than the traditional physical search. In fact, passengers subjected to secondary screening at Phoenix Sky Harbor International Airport, when given a choice between a physical pat down and a full-body scan, choose the latter 90 percent of the time, according to TSA. Civil libertarians counter that most people don’t know exactly what the images entail.

“Determining how the public feels about this is going to affect the future of it,” Howe says.

To address the privacy concern, TSA has asked manufacturers to tweak the algorithm to blur the face in the image. Certain backscatter systems offer what may be a more desirable privacy feature: the subject’s body is presented not as a full image, but instead as a white outline reminiscent of the chalk outline at a crime scene. Threat objects are superimposed.

To boost privacy further, the TSO who views the full scans is sequestered from the checkpoint. If the TSO spots a potential threat, he or she radios the checkpoint to order a pat down. In addition, the TSA’s policy requires that the scan images be deleted the moment review of the scan has been completed, Howe says. Asked about the value that such threat images might have in criminal investigations, prosecutions, or for intelligence, Howe says the TSA wrestled with the question, but opted to make a clear commitment for the sake of privacy.

“If [a suicide bomber] was going to get screened, they’d have blown themselves up already. And if you call over law enforcement, you’re not going to need the image,” because they will have the actual item, Howe says.

As of this summer, the TSA operated backscatter machines manufactured by American Science & Engineering Inc. (AS&E) at three airports—Los Angeles International, JFK, and Phoenix—for secondary screening versus a pat down. A total of 38 L-3 millimeter wave machines were in use at nine major airports for primary continuous screening, with three more airports planned by the end of the year, says Howe.

Howe notes that a millimeter wave scan takes 15 seconds compared to the backscatter’s 40 seconds—extra time that adds up at high-volume checkpoints.

Checkpoints also still use magnetometers. Given the prevalence of nonmetallic threats and the prevalence of harmless metal items both on—and in—passengers’ bodies, such as medical devices, Joe Reiss, vice president of marketing for AS&E, questions the ongoing value of magnetometers.

Howe, however, predicts that walk-through magnetometers will be present at TSA checkpoints for the foreseeable future. Each one costs about $5,000, while a new millimeter wave scanner costs roughly $200,000.

As for the privacy issue—it’s not going away. Cathleen A. Berrick, director of homeland security and justice issues for the independent Government Accountability Office, tells Security Management that the TSA has yet to fully allay privacy concerns surrounding the use of full-body scans.

Special needs. Some passengers, such as those with casts or prostheses, need special consideration when going through a screening checkpoint. TSA observes strict procedures to protect the rights and dignity of all passengers with disabilities. The question is how to meet security objectives without causing distress to these special-needs passengers.

With that in mind, TSA policy allows TSOs to inspect and touch devices like prostheses, but agents cannot compel travelers to remove them for inspection or screening. That’s where the technology can help.

To mitigate the risk presented by these devices, TSA, working with the imaging company Spectrum San Diego, Inc., developed CastScope. Roughly the size of an office water cooler, CastScope features a moveable backscatter array approximately the length of a person’s forearm or lower leg. As with full-body backscatter scanners, the system’s x-rays penetrate casts or prostheses to reveal any threat objects within. Each scan takes only 2.5 seconds, according to the company.

TSA began pilot testing of the CastScope early in 2007. It has since purchased 37 of the machines, according to the agency.

Trace Detection

Explosives trace detection (ETD) systems, like the name implies, are used to test for explosive residue on passengers and their effects, typically carry-ons.

The TSA’s first major attempt at ETD technology was a misfire: explosives detection trace portal machines, commonly referred to as “puffers.” Passengers stood in the portals, their arms raised. A quick puff of air dislodged solid particles from the passengers skin, hair, and clothing, which the machine then vacuumed up for analysis. The machines, however, tested in relatively sterile lab environments, were quickly fouled—and thus foiled—by the high volume of particulates in airport air, and as a result, they didn’t work. The TSA has shelved the technology indefinitely.

Meanwhile, there has been progress with other new technologies designed to detect trace elements of explosives, including liquids, which became a concern after a terrorist plot was uncovered in the United Kingdom in 2006. That plot entailed the use of liquid explosives to bring down an airplane headed for the United States.

Two Smiths Detection devices used by the TSA, the IONSCAN 400B and the SABRE 4000, rely on a process called ion mobility spectrometry to test for the presence of explosives (whether liquid or solid), illegal drugs, or chemical agents. The process is similar to that employed by many smoke detectors. Sample material is given an electrical charge, then passed through an electrical field to see how fast it moves. The speed of the material determines its composition.

The IONSCAN consists of equipment that is about the size of a microwave oven. An operator must take a sample using a swab—such as from the inside of a suspect bag—and drop it into the machine for analysis.

The SABRE miniaturizes the process into a handheld device tipped with a sensor probe that is used to “sniff” the air around a suspect object, such as the seal on a bottle containing liquid or gel. The SABRE’s key advantage is speed, due mainly to elimination of the swab step. An entire test can be conducted in as little as 20 seconds, according to Smiths.

Another new scanning device is the Fido explosives detector, which is manufactured by ICx Nomadics. It also “sniffs” around suspect areas and objects to detect explosives vapors, but it employs different technology to detect threats. The technology, licensed from the Massachusetts Institute of Technology, is based on chemiluminescence, the property that makes glow sticks glow. When explosive materials interact with Fido’s proprietary chemistry, they light up, and the device detects that luminescence.

Fido is currently in use by the TSA at 70 airports nationwide, according to Patrick Dempsey, ICx’s vice president of direct sales. ICx hopes to expand Fido technology to detect a broader range of threats, Dempsey says.

Another product TSA plans to evaluate is called the explosives particle analysis kit (XPAK), developed by RedXDefense, initially for military applications. The portable array, the size of a flattened shoebox, features an eyepiece and a removable wand, resembling a household lint roller, that is inserted in the side.

To test for explosives, the user covers the wand with a fresh, disposable paper sleeve, swabs the test area, and inserts the wand into the device. For the test, the system sprays the inserted wand with proprietary ink. Then, the user activates an internal ultraviolet lamp, and looks through the eyepiece. The ink is fluorescent, but explosives eliminate its fluorescence. Thus, any dark areas on the wand indicate the presence of explosives.

Currently, XPAK’s ink only detects organic explosives, but the company plans to field an ink capable of detecting inorganic compounds used in some “homemade” explosives, like ammonium nitrate and urea nitrate, says Sarah Toal, RedXDefense’s chief chemist.

The Next Generation

Researchers at the government’s national laboratories are working with funding from the TSA and the Department of Homeland Security’s Directorate for Science and Technology to see whether technologies from other fields can be adapted for airport security screening.

One example is magnetic resonance imaging (MRI). A 2006 call for new technologies to detect suspect liquids and gels (in response to the U.K. terrorist plot) coincided with ongoing work at Los Alamos National Laboratory to develop an MRI-type device with a magnetic field weak enough to read the subtle electromagnetic signatures of the brain, “see” a fetal heart beat, or be used to evaluate patients with implanted medical devices containing metal, like pacemakers.

A standard-strength MRI machine, used at a security checkpoint, might rip bags containing metal items to shreds, pull bystanders’ keys from their pockets, and send nearby magnetometers haywire. But a low strength MRI could help TSA scan liquids without restricting the amount or requiring special packaging.

“I think that’s DHS’s ultimate goal, but we’re a long way from that,” says Michelle Espy, the researcher and team leader working on the device, called the superconducting quantum interfering device, or SQUID. Espy’s team hopes to have a prototype built by the end of the year.

MRI machines use their magnetic fields to orient the existing magnetic fields around the nuclei of hydrogen atoms, then re-orient the fields slightly with radio waves. Detection of the changes in the fields produce clear images of the body’s soft tissues, which is difficult with x-rays.

Espy explains that the SQUID device would not read densities or atomic weights like current x-ray machines but rather it would detect how different chemicals react to magnetic fields. The device would rely on fields no stronger than those present in the everyday world. Ideally, Espy explains, the SQUID device would assay a child’s juice box packed in a carry-on and determine its contents as safe despite the container’s foil liner, and without damaging anything.

Remote testing. Another futuristic idea being pursued in the lab is the potential to test substances from a distance. At Oak Ridge National Laboratory in Tennessee, researcher Thomas Thundat is pursuing an explosives detection technology that holds the promise of “standoff” explosives trace detection from 20 or more meters away.

Oak Ridge’s standoff explosives detection research is based on spectroscopy, the process by which a substance’s chemical composition is determined through analysis of how it refracts energy, sometimes visual light—in this case, infrared energy from a quantum cascade laser. A relatively new technology relying on semiconductors, quantum cascade lasers are “eye safe,” Thundat says. They have already been commercialized for industrial chemical detection.

The technology has both high sensitivity and selectivity on small chemical traces, 100 times smaller than a fingerprint, either up close or at “tens of meters.” The technology also has the promise of hand-held portability. A likely obstacle, Thundat concedes: high cost per unit, which he attributes to a limited market for the technology, but that could change as the market grows.

Separate research at Oak Ridge holds the promise of palm-sized test devices for taking vapor samples from the air near suspect objects. The technology relies on microelectromechanical systems (MEMS), in this case cantilevers, which Thundat compares to a diving board the width of a human hair and 1/100th its thickness.

In one experiment, one side of the MEMS cantilever is coated with a chemical that automatically binds to an explosive compound present in vapor form. When that chemical reaction occurs, the cantilever bends, and the MEMS device detects the resistance. The real challenge, Thundat says, is to develop chemicals that attract specific explosive compounds selectively.

Another possible MEMS application involves what Thundat calls “deflagration,” essentially igniting trace explosive molecules present in air vapor form by heating the cantilever to 600 degrees Celsius—which is easy given its small size. Each compound’s ignition would have a specific signature, theoretically readable by the device. Thundat is still pursuing proof-of-concept for the deflagration concept, he says.

The most futuristic idea of all, however, is that screening can somehow be made effective but painless for travelers. Smiths Detection’s Laustra says forthcoming innovations are likely to include x-ray machines with alternative belts that automatically divert suspicious bags to secondary screening, so TSOs don’t have to stop the belts completely to remove suspect bags by hand. And Smiths Detection plans by 2010 to field a concept for what Laustra calls a “lane of truth,” a seamless, largely automated security checkpoint that would offer unintrusive screening that barely slows passengers’ progress from the check-in counter to the gate.

TSA shares that objective, says Howe. It could be achieved through a combination of identity verification, behavioral threat assessment, and technology, she says, adding, “I think there is a vision in which you could be going through screening and not even know it.”

Joseph Straw is an assistant editor at Security Management.