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Backscatter X-ray Technology

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"Backscatter" X-Ray Screening Technology

Latest News | Background | Resources | Profiling | Legislative History | References

Post-September 11, airline travel security has invoked the increased use of technology and better training of security personnel as a means of improving travel security. Some of these proposals, such as improved training for airport screeners, checking all bags for bombs, strengthening cockpit doors, and placing air marshals on flights, do not implicate privacy interests and are sound security measures. Others, however, present privacy and security risks to air travelers because they might create data files directly linked to the identity of air travelers. These files if retained could provide the basis for a database of air traveler profiles.


In 1895 x-rays1 were discovered by Wilhelm Röntgen.2 This discovery of how to look through an object to observe details beneath has advanced to include new techniques. One such technique called "backscatter" X-Ray is based on "the emergence of radiation from that surface of a material through which it entered. Also used to denote the actual backscattered radiation.3"

The application of this new x-ray technology to airport screening uses high energy x-rays that are more likely to scatter than penetrate materials as compared to lower-energy x-rays used in medical applications. Althought this type of x-ray is said to be harmless it can move through other materials, such as clothing.

A passenger is scanned by rastering or moving a single high energy x-ray beam rapidly over their form. The signal strength of detected backscattered x-rays from a known position then allows a highly realistic image to be reconstructed. Since only Compton scattered x-rays4 are used, the registered image is mainly that of the surface of the object/person being imaged. In the case of airline passenger screening it is her nude form. The image resolution of the technology is high, so details of the human form of airline passengers present privacy challenges.

Backscatter X-Rays and Transportation Screening

Recently plans were announced by the Transportation Security Administration to propose the trial use of backscatter x-ray for passenger screening at several U.S. airports. EPIC will make available on this page aviation security and privacyrelated documents it obtains from the government under the Freedom of Information Act law about the adoption of "backscatter" x-ray technology intended for use in screening air travelers.

The stated goal of these new proposals is to rely on technology to reduce the "hassle factor" in airports and to reduce security threats. The core idea is to focus security resources on suspicious travelers, while ensuring that most people are not inconvenienced by heightened security. Terrorists, however, have been known to go to great lengths to look like most people. Will a technology that will capture detailed images of potentially all airline travel passengers lead to greater safety? Current technology can successfully detect dangerous substances, firearms and other weapons without backscatter x-ray imaging of passengers. Can the goal of safe air travel be reached without reproducing a digital image of a passenger's body? It has long been recognized by security experts that it is impossible to eliminate all threats to airline travel. Is the application of "backscatter" x-ray technology a deterrent and not a solution to perfect airline travel safety? If this is true, then is the trade off in passenger privacy worth the effort to deter terrorists? The application of security technology and increased passenger screening has also resulted in an increased detection of non-violent criminal offenses. Is the application of "backscatter" x-ray technology to screen airline passengers more than just a means of detecting terrorists?

Latest News


Identification Schemes


Other Documents


  • Paper on the limitations of profiling, Roger Clark, Australia National University.
  • ACLU testimony before White House Commission on "Civil Liberties Implications of Airport Security Measures" (September 5, 1996).
  • Letter to Privacy Journal editor Robert Ellis Smith from the FAA denying Smith's request for a copy of the FAA Security Directive on identification of airline passengers.
  • HotWired article "Fear of Flying" on proposals. (September 11, 1996).

Other Airline Passenger Screening Resources

  • FAA Proposes Profiling Regulations. The Federal Aviation Administration published proposed regulations on April 19, 1999, governing "Security of Checked Baggage on Flights Within the United States." The draft rules detail the use of computer pofiling techniques to identify suspicious passengers.
  • Airline Passenger Profiling Goes Into Effect. The Computer Assisted Passenger Screening System was scheduled to be phased in nationwide beginning on January 1. Under the system, passengers who "fit the profile" will be selected for heightened security measures, which can include a thorough search of their luggage, intrusive personal questioning, tagging of luggage with orange tape, and a physical escort from the check-in counter to the airport gate by security personnel. The ACLU is providing an online complaint form for passengers targeted by the profiling system.
  • Microsoft Chief Architect Charles Simonyi tells what happens when you "fit the profile" (from Slate).
  • Proposed FAA rule for collecting personal information including name, address, Social Security Number, Date of birth and next of kin for every domestic passenger.
  • General Account Office report, Aviation Safety and Security: Challenges to Implementing the Recommendations of the White House Commission on Aviation Safety and Security (Testimony, 03/05/97, GAO/T-RCED-97-90).
  • The Gore Commission has released its final report recommending passenger profiling. A coalition of 17 groups has sent a letter to Gore opposing ID checks, profiling, new x-ray technologies and excessive secrecy by the FAA in making decisions.

Legislative History

HR 1271. FAA Research, Engineering, and Development Authorization Act of 1997. Funds FAA projects for new surveillance technologies such as advanced x-ray systems for individuals. Introduced on 4/10/97 by Morella (R-Md). Referred to the House Committee on Science. Approved by Commitee 4/16/97. Reported to the House H. Rept. 105-61 (CR H1714) on 4/21/97. Measure adopted on 4/29/97, RC #95 (414-7), (CR H1995). Referred to Senate Committee on Commerce, Science and Transportation (CR S3843) on 4/30/97.

Bill Passed the Senate: 11/13/1997
Mr. Sensenbrenner moved that the House suspend the rules and agree to the Senate amendments: 2/3/1998
Bill Passed the House by a voice vote: 2/3/1998 3:07pm:
Bill Signed into Law by President Clinton: 2/11/1998
Became Public Law No: 105-155.



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Last Updated: July 11, 2005
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