Existing and Potential Standoff Explosives Detection Techniques (2004)

In its deliberations, the committee focused its recommendations to meet its charge as expressed in its statement of task (Appendix A). Therefore, the committee’s recommendations fall into four main areas outlined in its task: characteristics of explosives, signal discrimination, detection systems, and areas of research.

In its statement of task, the committee was asked to describe the characteristics of explosives, bombs, and their components that are or might be used to provide a signature for exploitation in detection technology. The committee makes the following series of recommendations based on this aspect of the committee’s charge.

As noted in Chapter 4, the ability to detect explosive vapors is hampered by the lack of volatility of many energetic materials and bomb casings that help to confine vapors emitted by explosives. That being said, many explosive compounds do contain volatile impurities that can serve as markers indicating the presence of explosives. An understanding of the vapor plume dynamics may provide new insights into detection methodologies for these materials.

Also noted in Chapter 4 was the fact that strong oxidizing agents present in all explosives must make use of one or more of the most electronegative elements. Currently, IMS technology utilizes the presence of these electronegative elements to detect explosives. Research into analysis by nitrogen and oxygen composition may yield additional means of explosives detection. As noted in the FBI presentation to the committee by Dr. Bermeister, terrorists will adapt when barriers prevent them from undertaking their attacks utilizing traditional explosives and methods. It is therefore prudent to be aware of breakthroughs and advances in the development of new explosives, particularly those that utilize novel chemical functionality.

While most of the focus in explosives detection has been on physical properties of chemical explosives and how those properties can be exploited, it is essential to take into account not just the explosive but all other components of the bomb, including those who assemble the device and those who deliver it. As opposed to other methodologies that analyze potential bombers, for example, gait analysis, physiological changes resulting from exposure to explosive materials may be quantifiable. Human exposure biomarkers are addressed in detail in Chapter 5.

In its statement of task, the committee was asked to pay particular consideration to discriminating possible signals from explosives from background and interferents that can be anticipated in real applications. Development of a database of likely background conditions for use in system testing and implementation, and exploration methods for monitoring changes in background in real time would permit detection of weaker signals, and thus expand the possibilities of standoff detection. Research in detection of real-time changes in ambient conditions is essen-

tial for explosives detection because of the variety of scenarios where explosives detection must be made. Only by overcoming the challenge of detecting a signal in a dynamic, noisy background environment will effective standoff detection be achieved.

The following findings and recommendations are made by the committee in response to its charge to discuss the potential for integrating detection techniques into detection systems that would have sufficient sensitivity without an unacceptable false positive rate. A number of presenters to the committee remarked that there is no “silver bullet” explosives detection. It is highly unlikely that a single means of detection will be effective in all the environments (e.g., indoor/outdoor, military/civilian) and for all potential explosives (e.g., military ordnance, improvised explosives, ammonium nitrate-based explosives) where standoff explosives detection is required. As a result, multiple detectors embedded in a decision-making system are required. The committee focused much of its attention on this issue.

The effectiveness of detection systems depends in great part on the scenario and threat parameters assumed in building the system. This must be appreciated in any research and development effort.

The ability to deploy multiple, orthogonal detectors, each measuring different aspects of the same potential threat is needed to provide better overall detector performance. In order to successfully combine multiple detectors into an integrated, decision-making detection system, the committee recommends the following areas for research:

The committee was asked to propose areas of research that might be expected to yield significant advances in practical explosives and bomb detection technology in the near, mid, and long term. Some of the recommendations for research were presented earlier in this chapter. The recommendations below are for additional areas of research that were identified by the committee as it analyzed the challenges involved in effective standoff detection. In keeping with the committee’s statement of task, these recommendations are divided into research expected to yield significant advances in the near, mid, and long term:

Wide-area surveillance depends heavily on the distribution of multiple low-cost sensors, and effective integration of the data received by these sensors. The development of inexpensive sensors is presently a field of active research for a multitude of applications. A thorough overview of the current state of sensor research would provide a useful baseline for

determining advances needed in sensors for standoff explosives detection applications.

As discussed in Chapter 5, a number of imaging methods are currently under active and extensive development for use in explosives detection. While some of these methods are either in use now or are close to deployment, significant limitations still remain for their use as effective standoff explosives detection. For imaging, atmospheric water and the need for significant object of interest/background temperature differentials pose limitations on where and how these detectors can be used. In addition, in most cases detection using spectroscopy is relatively immature compared to imaging.

Research into the pathways and processes involved in sensing by animals has made great strides in recent years. Additional effort is now needed into how best to integrate this understanding in the development of low-cost biomimetic devices.

Effective standoff detection requires not only identification of the threat, but action to intercept the threat before major damage can be inflicted by the perpetrator. Preemptive detonation has been a focus of research, but its impact on innocent bystanders and equipment still makes it impractical for deployment. Research into preemptive disabling of explosive devices should build on the knowledge gained from the development of active sensing technologies.

As the committee heard many times over the course of this study, the challenges posed in the development of effective standoff explosives detection technologies are extensive and dynamic. Signal discrimination, mitigation of false alarms, the emergence of new explosive compounds that can potentially thwart an explosives detector are just a few of the difficulties that must be addressed. In light of these issues, it is essential that researchers and program managers be willing to engage in high-risk/ high-payoff research. Fresh, bold approaches using innovative thinking should be encouraged from the outset, even when the barriers to implementation initially may appear to be formidable.