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TABLE 3-1  Passenger Screening Technologies Based on Imaging

Detection technology



Millimeter waves

Wall units
Enclosed spaces

Requires more than a single view
Requires more than a single view
Could get a 360° view


Enclosed spaces

Requires more than a single view
Could get a 360° view

Source: Jankowski (1995a, b).

of the U.S. domestic air travel industry. However, the El Al screening system could serve as a model for a passengerprofiling method to help air carriers identify passengers who require more extensive screening.


Several emerging technologies can detect metallic and nonmetallic weapons, explosives, and other contraband material concealed under multiple layers of clothing by creating images that can be examined to discern these materials. No physical contact is involved. These are already used for a wide variety of security applications, such as screening visitors to correctional facilities and exit-screening employees to deter theft. Table 3-1 outlines some of the ways imaging devices could be implemented in an airport environment.

Imaging technologies either scan subjects for natural radiation emitted by the human body (passive imaging) or expose subjects to a specific type of radiation reflected by the body (active imaging). In either case, materials such as metallic weapons or plastic explosives, which emit or reflect radiation differently from the human body, are distinguishable from the background image of the body. These screening systems generate television-like digital images that can be evaluated by image processing and analysis methods. Images are viewed by an operator trained to identify potential threat objects in these images, sometimes with the assistance of image enhancing software that highlights unusual features. Although these technologies cannot detect objects concealed inside the body or in skin flaps, they are being considered for airport passenger screening because they would enable air carriers to screen for a wider variety of materials than they can with present screening systems. Two technologies under consideration use either x-ray or millimeter (or submillimeter) wavelength electromagnetic radiation. Figure 3-2 shows the electromagnetic spectrum, indicating the wavelength of x-ray and millimeter wave radiation in relation to other common sources of electromagnetic radiation.1

Passive Millimeter-Wave Imaging

A passive technology under investigation by the FAA operates in the millimeter-wave range (near 100 gigahertz) of


FIGURE 3-2 The electromagnetic spectrum.

1 Energy, frequency, and wavelength are fundamentally related. Energy is inversely proportional to wavelength (e.g., long wavelength radiation is low energy and low frequency; short wavelength radiation is high energy and high frequency).

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