Summary of Committee Recommendations
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.
CHARACTERISTICS OF EXPLOSIVES, BOMBS, AND THEIR COMPONENTS
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.
Recommendation: Research into the vapor space about the bomber may lead to improved means of explosives detection. An increased quantitative understanding of vapor plume dynamics is required
for application to explosives with high-volatility components such as TATP.
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.
Recommendation: Improved detection systems will lead to development of new explosives. Research is needed on the identification and characterization of new chemical explosives that do not utilize nitrogen and have very low vapor pressures, for example, ionic liquids.
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.
Recommendation: Research is needed on biological markers related to physiological changes of persons associated with bomb making and bomb delivery and based on the chemical composition of the explosive.
SIGNAL DISCRIMINATION FROM BACKGROUND
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.
Recommendation: Because discrimination of a useful signal in a noisy environment is always a problem, a research effort should be aimed at determining baseline ambient conditions and detecting changes in ambient conditions in real time.
DETECTION SYSTEMS INTEGRATION
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.
Recommendation: Research into both new sensors and new systems of real-time integration and decision making is needed. The sensor research agenda should emphasize the principle of orthogonality in mathematical consideration, sensor system design, and design of information leading to true detection.
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:
Recommendation: Research is recommended into methodologies to quantify system effectiveness (SE) for systems of sensors (a detection system) and for systems of detection systems allowing for noisy input from many sensors. Of particular importance is the definition and evaluation of a full spectrum of “false positive” signals rang-
ing from detector reliability, legitimate signals that do not represent true threats, or operator interpretation of detector signals. Appropriate ROCs and other measures of performance for such systems should be developed.
Recommendation: Research is needed into the development of scenario-threat parameters-decision trees for real-time decision making.
Recommendation: Research is needed on the integration of information from distributed orthogonal sensors to achieve real-time conflict resolution and decision making with high system effectiveness, and on integration tools based on data fusion and decision fusion. In addition, research coupling parallel sensors via decision fusion with sequential sensor systems may provide valuable insights.
Recommendation: Research is recommended to envision and devise real-time sensor system threat detection that adapts to new threats, new backgrounds, and new threats that behave like background. A system that autonomously evolves should be a focus of research, including methods to evolve the system design to increase system effectiveness and orthogonality, given detection anomalies.
AREAS OF 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:
Research Recommendations for Near-Term Technology Advances
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.
Recommendation: Research is recommended into rapid, remote collection and concentration of explosives samples and into distributed, low-cost sensors. Included here are small (nano) and perhaps mobile sensors, distributed arrays of sensors, and the use of convective streams with or without airborne adsorbing particles to gather chemical samples.
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.
Recommendation: Research is needed on new spectroscopic and imaging methods employable at a distance (passive and active). Examples include terahertz and microwave imaging and spectroscopy and X-ray backscattering.
Research Recommendations for Mid-Term Technology Advances
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.
Recommendation: The committee recommends continued research into biomimetic sensing based on animals, but research should focus on distributed, low-cost sensors.
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.
Research Recommendations for Long-Term Technology Advances
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.
Recommendation: Research is needed on biological markers related to physiological changes in persons associated with bomb making and bomb delivery and based on the chemical composition of the explosive.
Recommendation: Feasibility studies should be developed on the ideas suggested in Chapter 7 to assess their potential in sensors suitable for standoff detection.