The combination or fusion of data from multiple complementary sensors can potentially improve system performance in many explosives and weapons detection applications. The motivations for fusion can include improved probability of detection; reduced false alarms; detection of an increased range of threats; higher throughput and better resilience to adversary countermeasures. This paper presents the conclusions of a study which surveyed a wide range of data fusion techniques and examples of the research, development and practical use of fusion in explosives detection. Different applications types such as aviation checkpoint, checked baggage and stand-off detection are compared and contrasted, and the degree to which sensors can be regarded as ‘orthogonal’ is explored. Whilst data fusion is frequently cited as an opportunity, there are fewer examples of its operational deployment. Blockers to the wider use of data fusion include the difficulty of predicting the performance gains that are likely to be achieved in practice, as well as a number of cost, commercial, integration, test and evaluation issues. The paper makes a number of recommendations for future research work.
Following the 2001 Anthrax letter attacks in the USA, there has been a continuing interest in techniques that can detect
or identify so-called 'white powder' concealed in envelopes. Electromagnetic waves (wavelengths 100-500 μm) in the
terahertz frequency range penetrate paper and have short enough wavelengths to provide good resolution images; some
materials also have spectroscopic signatures in the terahertz region. We report on an experimental study into the use of
terahertz imaging and spectroscopy for mail screening. Spectroscopic signatures of target powders were measured and,
using a specially designed test rig, a number of imaging methods based on reflection, transmission and scattering were
investigated. It was found that, contrary to some previous reports, bacterial spores do not appear to have any strong
spectroscopic signatures which would enable them to be identified. Imaging techniques based on reflection imaging and
scattering are ineffective in this application, due to the similarities in optical properties between powders of interest and
paper. However, transmission imaging using time-of-flight of terahertz pulses was found to be a very simple and
sensitive method of detecting small quantities (25 mg) of powder, even in quite thick envelopes. An initial feasibility
study indicates that this method could be used as the basis of a practical mail screening system.
The U.S. Department of Homeland Security's Standoff Technology Integration and Demonstration Program is designed
to accelerate the development and integration of technologies, concepts of operations, and training to defeat explosives
attacks at large public events and mass transit facilities. The program will address threats posed by suicide bombers,
vehicle-borne improvised explosive devices, and leave-behind bombs. The program is focused on developing and testing
explosives countermeasure architectures using commercial off-the-shelf and near-commercial standoff and remotely
operated detection technologies in prototypic operational environments. An important part of the program is the
integration of multiple technologies and systems to protect against a wider range of threats, improve countermeasure
performance, increase the distance from the venue at which screening is conducted, and reduce staffing requirements.
The program will routinely conduct tests in public venues involving successively more advanced technology, higher
levels of system integration, and more complex scenarios. This paper describes the initial field test of an integrated
countermeasure system that included infrared, millimeter-wave, and video analytics technologies for detecting person-borne
improvised explosive devices at a public arena. The test results are being used to develop a concept for the next
generation of integrated countermeasures, to refine technical and operational requirements for architectures and
technologies, and engage industry and academia in solution development.
We report on the transmission and reflection terahertz (THz) spectra of the high explosives RDX and PETN. These
common military explosives are compared to simulants L-tartaric acid and sucrose, respectively. The use of these
simulants enables researchers to develop many aspects of THz spectroscopy for explosives detection without the need
for live explosives. Further, we discuss the effect of sample preparation on the THz spectrum of RDX and demonstrate
that experiments performed on different terahertz instruments at multiple laboratories show quantitative agreement
between spectra recorded with four different instruments.
There has been intense interest in the use of millimetre wave and terahertz technology for the detection of concealed
weapons, explosives and other threats. Electromagnetic waves at these frequencies are safe, penetrate barriers and have
short enough wavelengths to allow discrimination between objects. In addition, many solids including explosives have
characteristic spectroscopic signatures at terahertz wavelengths which can be used to identify them.
This paper reviews the progress which has been made in recent years and identifies the achievements, challenges and
prospects for these technologies in checkpoint people screening, stand off detection of improvised explosive devices
(IEDs) and suicide bombers as well as more specialized screening tasks.
Terahertz radiation, which lies between microwave and infrared, has been shown to have the potential to use very low
levels of this non-ionising radiation to detect and identify objects, such as weapons and explosives, hidden under
clothing. This paper describes recent work on the development of prototype systems using terahertz to provide new
capabilities in people screening. In particular, it explores how hyperspectral terahertz imaging and the use of both
specularly reflected and scattered terahertz radiation can enhance the detection of threat objects.
There is a need for ever more effective security screening to detect an increasing variety of threats. Many techniques employing different parts of the electromagnetic spectrum from radio up to X- and gamma-ray are in use. Terahertz radiation, which lies between microwave and infrared, is the last part to be exploited for want, until the last few years, of suitable sources and detectors. Terahertz imaging and spectroscopy has been shown to have the potential to use very low levels of this non-ionising radiation to detect and identify objects hidden under clothing. This paper describes recent work on the development of prototype systems using terahertz to provide new capabilities in people screening, both at security checkpoints and stand-off detection for remote detection of explosives and both metallic and non-metallic weapons.
We report the use of a terahertz pulsed imaging technique for three-dimensional chemical mapping. Terahertz radiation reflected from a sample was measured pixel-by-pixel in time domain using a terahertz pulsed imaging system developed at TeraView Ltd, UK. The recorded terahertz waveforms were then transformed into frequency domain using time-partitioned Fourier transform. Structural maps of samples were obtained by analyzing the terahertz time-domain data whilst chemical maps were obtained from terahertz spectral data sets. For a sample comprising chemical A at the surface of a polyethylene pellet and chemical B buried inside the pellet, we have separated the component spatial patterns of the two chemicals using their spectral fingerprints. The reconstructed three-dimensional chemical maps not only locate the chemicals in the object, but also identify each chemical. We also demonstrate the capabilities of terahertz pulsed imaging for non-destructive analysis of coating thickness and quality, and for detecting and identifying explosive materials such as RDX.
We describe the latest progress on two new terahertz (THz) prototype systems for security screening applications. Firstly, we show a terahertz stand-off detection system, working at a distance of 0.5 m, and with a dynamic range of ~60 dB. This allows the measurement of spectral features from 0.1 to 2.5 THz. Using this prototype, we present the reflection spectrum of an explosive material collected at 0.5m stand-off and compare it with the predicted spectrum. Secondly, a hand held wand using multiple terahertz detectors has been assembled. This resembles a metal detector wand in operation, and is designed for detecting explosives as well as both metallic and non-metallic weapons hidden under clothing or possibly in bags. The first data from this system is presented, showing that objects can be distinguished using their spectral features.
The terahertz spectrum of the explosive RDX has been measured using a conventional Fourier transform infrared spectroscopy and by terahertz pulse spectroscopy in transmission and reflection modes. Seven absorption features in the spectral range 5-120 cm-1 have been observed and identified as the fingerprints of RDX explosive. Furthermore, a sample consisting of RDX-based explosive, mounted side by side with lactose and sucrose pellets, has been imaged using a terahertz pulse imaging system. The recorded terahertz images and their spectral data have a spectral resolution of 1 cm-1 and cover a spectral range of 5-80 cm-1. This broad spectral coverage enables the spatial distribution of individual chemical substances of the sample to be mapped out. We also discuss the application of Principal Component Analysis and Component Spatial Pattern Analysis to the automatic identification of materials, such as explosives, from terahertz imaging.
Recent events have led to dramatic changes to the methods employed in security screening. For example, following the failed shoe bombing, it is now common for shoes to be removed and X-rayed at airport checkpoints. There is therefore an increasing focus on new Recent events have led to dramatic changes to the methods employed in security screening. For example, following the failed shoe bombing, it is now common for shoes to be removed and X-rayed at airport checkpoints. There is therefore an increasing focus on new technologies that can be applied to security screening, either to simplify or speed up the checking process, or to provide additional functionality. Terahertz (THz) technology is a promising, emerging candidate. In previous publications we have shown how our THz pulsed imaging systems can be used to image threat items, and have demonstrated that explosive materials have characteristic THz spectra. We have also demonstrated that nonmetallic weaponry can be imaged when concealed beneath clothing. In this work we examine more closely the properties of barrier and potential confusion materials. We demonstrate that barrier materials have smooth spectra with relatively low attenuation. We further demonstrate that the terahertz spectra of several common chemicals and medicines are distinct from those of threat materials.
Recent events have accelerated the quest for ever more effective security screening to detect an increasing variety of
threats. Many techniques employing different parts of the electromagnetic spectrum from radio up to X- and gammaray
are in use. Terahertz radiation, which lies between microwave and infrared, is the last part to be exploited for want,
until recently, of suitable sources and detectors. This paper describes practical techniques for Terahertz imaging and
spectroscopy which are now being applied to a variety of applications. We describe a number of proof-of-principle
experiments which show that Terahertz imaging has the ability to use very low levels of this non-ionising radiation to
detect hidden objects in clothing and common packing materials and envelopes. Moreover, certain hidden substances
such as plastic explosives and other chemical and biological agents may be detected from their characteristic Terahertz
spectra. The results of these experiments, coupled with availability of practical Terahertz systems which operate outside
the laboratory environment, demonstrate the potential for Terahertz technology in security screening and counterterrorism.