Appendix B
Glossary
Active.
Those measurements that require external stimulation (e.g., incident electromagnetic radiation) or direct sample collection to obtain data.
Data Fusion.
Combination of unprocessed data from multiple sensors to create unified input for a detection method or system.
Decision Fusion.
Combination of results from multiple detectors to create a decision.
Detector.
A data collection and processing technology. In this report, a “detector” both collects and evaluates data in order to provide assessment regarding the presence of characteristics or indications of explosives or explosive devices. The “detectors” are contrasted with “sensors,” which collect data but do not evaluate the data with respect to the presence of explosives.
False Negative.
A detector reading suggesting the absence of an explosive or explosive devices when explosives are, in fact, present. The probability of observing a false negative is referred to as the “false-negative probability” or “false-negative rate.”
False Positive.
A detector reading suggesting the presence of an explosive or explosive device when explosives are not present. The probability of observing a false positive is referred to as the “false positive probability” or “false positive rate” and is equivalent to the specificity of the detector.
Orthogonal Detection Methods.
Two or more explosive detection technolo-
gies that are mutually independent. That is, they detect independent characteristics of the explosive device.
Passive.
Those measurements that develop the data for a threat analysis from inputs that are freely arriving at a sensor or detector. The item being analyzed is neither disturbed nor subjected to external manipulation to collect data. Examples include collecting images (e.g., thermal infrared or terahertz) or spectroscopic data without external illumination (though it does include those based on emission profiles) or chemical sampling without directly probing of the source or target.
Positive Predictive Value.
The probability that a detector reading suggesting the presence of explosives or explosive devices corresponds to the true presence of an explosive or explosive device.
Remote.
For explosives detection, a far-enough distance that the detector operator or vital assets are not severely damaged if the explosive device detonates.
ROC (Receiver Operating Characteristic) Curve.
A plot of the sensitivity (probability of observing a true positive) versus the converse of specificity (probability of observing a false positive) for the full range of possible decision criteria.
Sampling.
In this report, the collection of a physical sample for analysis (e.g., physical contact, wiping, active or passive collection of vapors, and active or passive collection of particles).
Scenario.
A posited future state with an allied set of possible future events—a story line—that is used to explore concepts. Scenarios are thought experiments; they are basic tools for being anticipatory. A scenario serves as a working prototype of an idea in a context; developing that scenario objectively exposes hidden assumptions and contingencies about the environment, actors, or context.
Sensitivity.
A detection approach is sensitive when it alarms if the substance of interest is present.
Sensors.
A data collection technology. Sensors pass along data without determination of the presence or absence of explosives, explosive devices, or their accompanying characteristics, whereas detectors measure data and evaluate of the data with respect to the presence of explosives.
Specificity.
A detection approach is specific when it alarms only if the substance of interest is present.
Standoff Explosive Detection.
Passive and active methods for sensing the presence of explosive devices when vital assets and those individuals
monitoring, operating, and responding to the means of detection are separated physically from the explosive device. The physical separation should put the individuals and vital assets outside the zone of severe damage from a potential detonation of the device.
Systems Effectiveness.
“A measure of the degree to which an item can be expected to achieve a set of specific mission requirements and which may be expressed as a function of availability, dependability and capability” (Definitions of Effectiveness Terms for Reliability, Maintainability, Human Factors, and Safety, MIL-STD-721B, U.S. Department of Defense, Aug. 1966). For standoff explosives detection, system effectiveness could include detection system availability, maintainability, system ROC, and the probability of avoiding defeat.
Threat Parameters.
Characteristics of threats used in developing a threat analysis. These include, for example, delivery methods for a device, location and timing of a detonation, explosive composition, mass of explosive, other device components, and dispersed materials.
True Negative.
A detector reading suggesting the absence of explosives or explosive devices when no explosives are present. The probability of observing a true negative is referred to as the true negative rate or true negative fraction.
True Positive.
A detector reading suggesting the presence of explosives or explosive devices when explosives are present. The probability of observing a true positive is referred to as the true positive rate or true positive fraction and is equivalent to the sensitivity of a detector.
