DOE OSTI2011
Air travel is a popular mode of transportation. Each year, more than 600 million people board U.S. flights for business or pleasure. As demonstrated on 9/11, a coordinated terrorist strike on commercial airlines has devastating consequences where many lives could be lost and the nation’s economy could be crippled. The Transportation Security Administration (TSA) has worked diligently to enhance security at airports and on flights so that people and cargo can continue to move freely. Today, all passengers and every piece of checked or carry-on luggage are screened before they are permitted on an aircraft. X-ray systems and walk-through metal detectors allow security personnel to identify dangerous metal objects, such as guns and knives. A more complex problem is the detection of explosives, where detection technologies such as multiple-energy X-ray radiography, computed tomography (CT), full body scanners using millimeter wave and X-ray backscatter and other techniques are used to screen for explosives hidden in luggage, in cargo and on the people boarding the aircraft. Scientists and engineers at the Lawrence Livermore National Laboratory (LLNL) are working with the Department of Homeland Security (DHS), Science and Technology Directorate (S&T), Explosives Division (EXD) to help improve aviation security by evaluating and enhancing the performance of next-generation explosives detection technologies. LLNL is providing subject matter expertise to TSA for their multi-billion dollar procurements of explosive detection system (EDS) for the nation’s airports and provides recommendations for process and system improvements. To further improve aviation security, EXD is funding research at LLNL to develop advanced explosives detection technologies that can more accurately discriminate between a wide range of explosives and non-threat materials. One challenge with scanning for explosives is that some nonthreatening materials share similar characteristics with actual threats, leading to false positives or false alarms. When an alarm is generated, security personnel must review the scan images to clear the alarm or manually open and verify the bag’s contents, which can increase labor costs and lead to passenger delays. The Livermore efforts currently focus on CT-based applications. First developed for the medical field as a method for diagnosing disease, X-ray CT has become instrumental in various industrial Non-Destructive Evaluation (NDE) applications. Explosives detection equipment that incorporates CT uses a broad-spectrum X-ray beam to capture projections of an object, in particular, the objects inside a piece of luggage. The CT system then applies complex reconstruction algorithms to the projections to produce a three-dimensional representation of the luggage and its contents. Automated threat-detection algorithms (also referred to as threat-recognition algorithms) further process the images to separate each item and flag potential threats for further review (see Figure 1). Transportation security officers can then examine these images and the relevant data to determine whether further interrogation is needed. LLNL has also performed research on advanced X-ray carry-on bag inspection systems and is helping to better understand the performance of X-ray backscatter and millimeter wave passenger screening systems.