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Winter/Spring 2007 Vol. 7 No. 1

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Detecting New Threats in Airports

Travelers at Ronald Reagan Washington National Airport, ©Ken Cedeno/Corbis

Promising Technology May Be
the Wave of the Future

Over the past 30 years, the Federal Aviation Administration, and more recently the Transportation Security Administration, has funded the development of technologies that screen aircraft passengers and their luggage faster and better. But the detectors and screening devices currently in use aren't able to detect nonmetallic concealed objects or small traces of explosives.

Technologies using millimeter and terahertz waves -- a spectrum of electromagnetic waves with frequencies between infrared light and microwaves -- promise to do just that, according to a new report from the National Research Council. Universities, national laboratories, and the commercial sector are increasingly focusing on the research and development of devices using these waves to secure buildings, ports, and borders, and hopefully airports in the near future. So far, these technologies can detect nonmetallic objects concealed on people or in luggage but not whether they are explosives or weapons.

"Threats have evolved over time to include plastic and ceramic handguns and knives, as well as explosives that are not recognized by metal detectors," said James O'Bryon, chair of the committee that wrote the report. "Millimeter and terahertz wave technology could allow us to detect such threats in the future, and progress in this area, although limited, is encouraging."

Millimeter wave imaging technology, photo courtesy Pacific Northwest National LaboratoryOne key advantage of millimeter and terahertz waves over X-rays is that they are nonionizing, making them safer -- especially if used repeatedly on the same individual. A device using these waves works like a camera measuring the energy radiated or reflected by an object to create an image.

Two types of imaging techniques are currently being tested: active and passive. Passive imaging systems detect the energy naturally radiated by objects, revealing contrasts between warm and cold areas -- such as a cold metal weapon obscuring part of a warmer human body. Active imaging systems scan a subject with a beam of light and then detect the reflected energy, revealing concealed objects.

The resolution of the images from both types of system is still too low to recognize specific explosives or weapons, the report says. One way to solve the problem is to compare the images of objects to those in a database of known dangerous items. A computer program would try to match the object's image with at least one in the database. If a match is found, a security officer would perform a search or ask the person to remove the suspicious item. The database information would also help security officers search only individuals with items deemed suspicious by the computer program.

Another limitation of the imaging techniques is that they reveal anatomical details that a person could find embarrassing or consider a violation of privacy. This issue needs to be addressed rigorously by legal experts and psychologists, the committee said.

Because of such limitations, these technologies may have to be combined with other screening techniques, the report says. TSA should examine how to mix various screening technologies to enhance the detection of weapons and explosives.

Developing an effective millimeter/terahertz-wave screening device can be costly, the report notes. TSA should collaborate with universities, national laboratories, and businesses that have already invested extensively. TSA should also assess whether these technologies can realistically be deployed for transportation security.   -- Patrice Pages

Assessment of Millimeter-Wave and Terahertz Technology for Detection and Identification of Concealed Explosives and Weapons. Committee on Assessment of Security Technologies for Transportation, National Materials Advisory Board, Division on Engineering and Physical Sciences (2007, 88 pp.; ISBN 0-309-10469-6; available from the National Academies Press, tel. 1-800-624-6242; $18.00 plus $4.50 shipping for single copies).

James F. O'Bryon, chair of the O'Bryon Group, Bel Air, Md., chaired the committee. The study was funded by the Transportation Security Administration.

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Copyright 2007 by the National Academy of Sciences