International Journal of High Speed Electronics and Systems

Two primary goals of infrared spectroscopic detection are chemical identification and quantification. In order to accomplish these goals, a comprehensive and quantitative spectral library suitable for digital manipulation is required. To a large degree, the contents of such a library depend on the application. Since the primary application of the PNNL/DOE spectral library is for environmental monitoring, we have focused our efforts on hazardous pollutants, as well as a large variety of natural and anthropogenic chemicals. As a spin-off project and in collaboration with Dugway Proving Ground, we also had the opportunity to analyze a limited set of chemical warfare agents (CWAs). An example of such data appears below.

Infrared optical properties of VX [O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothioate] in the vapor and liquid phases. Refractive index data (top traces) are critical for modeling aerosol and reflection phenomena.

An approach for the passive standoff detection of surface contaminants by differential polarization FTIR spectrometry is proposed. The surface radiance modeling associated with the method is given. Unpolarized and polarized sensing measurements obtained with the CATSI sensor for the standoff detection of liquid agent VX deposited on high-reflectivity surfaces are presented. The analysis of results indicates that the differential polarization approach is well suited to mitigate sky radiance drifts, which favours unambiguous surface contaminant detections. An experimental and modeling study initiated to address the spectral polarization phenomenology is outlined. The design of an optimized FTIR sensor for differential polarization spectrometry measurements is discussed.

In order to assess the differences between background clutter using the CATSI instrument in direct (single-beam) and differential (double-beam) mode, a survey of background measurements was undertaken. Measurements include samples of sky, mountains, forest, buildings, roads and snow during springtime in the long wave infrared using both single-beam and double-beam interferometry. It is found that background distribution and statistics in these two modes are significantly different, with the differential mode presenting less variation than the direct mode. This may impact the ability to detect atmospheric contaminants. This analysis was performed in order to better understand the difference between operating a standard and a differential FTIR instrument.

We report advances in the signal processing of Multicomponent Raman Spectra of particulate matter. We evaluate laboratory and ambient samples collected in field experiments in Canada (during the Pacific 2001 Experiment, Vancouver, BC and at ALERT station, Nunavut, 2002). We discuss methodologies for signal processing the Raman spectra: de-noising and de-peaking, baseline reduction, and identification of chemical fingerprints. The ambient samples were collected near the surface in different environmental conditions during field experiments. In this article we compare and assess the methodologies performances and differences.

In the last few years, a number of researchers including our collaboration have assembled databases of terahertz (THz) time-domain spectroscopy (TDS) absorption spectra from bulk explosives. While this was a necessary and important step in demonstrating the feasibility of THz TDS for explosives detection, the goal of our research is to demonstrate selectivity of THz spectra from the clutter of background spectra coming from the substrate such as soil or sand. We have investigated THz TDS reflection spectra from sand with different grain sizes as well as from metallic powders in order to distinguish between the signals reflected from the rough surfaces compared to distributed reflections at finite depths in the granular material. With marker materials such as tartaric acid, which have absorption features in the 1-2 THz range, we have investigated the reflection spectra of granular substrates with marker chemicals, and compared this to reflection and transmission spectra of solid materials prepared in polyethylene sample pellets. In principle, the same experiments can then be performed using TNT, RDX, HMX and PETN, which all have characteristic features in the 0.5-8 THz frequency range. Absolute molecular absorption coefficients can be measured as well, and we include here preliminary values for RDX. A full analysis will be reported elsewhere.

The objective of this paper is to show that explosives may potentially be detected by passive standoff FTIR radiometry. It is demonstrated that many explosives exhibit a signature (fingerprint) in the longwave infrared (LWIR) region (i.e., 8 – 14 μm). Simulations using the radiative transfer model, MODTRAN4, clearly suggest that such materials can be identified when a thermal contrast exists between the material and its environment. The explosives considered in this study include octogen (HMX), trinitrotoluene (TNT), cyclonite (RDX), and the plastic explosives, C-4 and Detasheet-C. In addition, passive FTIR measurements of HMX have been performed in the field at standoff distances up to 60 m. The development of a passive standoff detection capability based on FTIR radiometry may be a potentially useful addition to the arsenal of measurement techniques that currently exist for the detection and identification of explosive threats.

Principal Components Analysis (PCA) is a common anomaly detection tool that was used in this work to detect organic and organophosphate analytes on soils using mid-infrared reflection-absorption spectroscopy. Detection is hindered by large variability in sample-to-sample soil reflectivity that is due to the random nature of the soil particle packing. Extended multiplicative scatter correction (EMSC) and Savitzky-Golay derivative preprocessing were examined as methods to reduce this variability and enhance detection capability. Second derivative preprocessing provided results that were at least as good as EMSC for detection and the simplicity of the derivative methodology makes it an attractive preprocessing approach. Typically, PCA is applied to all spectral channels and results from detection events are interrogated to identify a potential cause. In this work, PCA models were developed for specific wavenumber ranges corresponding to functional group frequencies with the objective of providing some classification capability. It was found that detection of CH₂, CH₃ and P=O stretching bands was possible; however, results for a –CH₂ scissors band was less encouraging and detection of O–H stretch, –C–C– skeletal stretch, and PO–C stretch modes was poor. Some limited classification capability may be possible, but it would be difficult to make a unique assignment of the analytes present using the strategies studied.

This paper presents a novel wavelet and support vector machine (SVM) based method for hyperspectral image classification. A 1-D wavelet transform is applied to the pixel spectra, followed by feature extraction and SVM classification. Contrary to the traditional method of using pixel spectra with SVM classifier, our approach not only reduces the dimension of the input pixel feature vector but also improves the classification accuracy. Texture energy features computed in the spectral dimension are mapped using polynomial kernels and used for training the SVM classifier. Results with AVIRIS and other hyperspectral images for land cover and benthic habitat classification are presented. The accuracy of the method with limited training sets and computational burden is assessed.

In this paper we assess the effect that clustering pixels into spectrally-similar background types, for example, soil, vegetation, and water in hyperspectral visible/near-IR/SWIR imagery, prior to applying a detection methodology has on material detection statistics. Specifically, we examine the effects of data segmentation on two statistically-based detection metrics, the Subspace Generalized Likelihood Ratio Test (Subspace GLRT) and the Adaptive Cosine Estimator (ACE), applied to a publicly-available AVIRIS datacube augmented with a synthetic material spectrum in selected pixels. The use of synthetic spectrum-augmented data enables quantitative comparison of Subspace-GLRT and ACE using Receiver Operating Characteristic (ROC) curves. For all cases investigated, Receiver Operating Characteristic (ROC) curves generated using ACE were as good as or superior to those generated using Subspace-GLRT. The favorability of ACE over Subspace-GLRT was more pronounced as the synthetic spectrum mixing fraction decreased. For probabilities of detection in the range of 50-80%, segmentation reduced the probability of false alarm by a factor of 3–5 when using ACE. In contrast, segmentation had no apparent effect on detection statistics using Subspace-GLRT, in this example.

The Advanced Responsive Tactically-Effective Military Imaging Spectrometer (ARTEMIS) is under development for tactical military applications and is the primary payload for the TacSat-3 satellite. The optical design for the telescope, imaging spectrometer, and high resolution imager is described.

The U.S. Army is actively pursuing 3D active imaging techniques using laser sources emitting at 1.5 μm. This eyesafe short wave infrared (SWIR) waveband is advantageous due to both the improved eye safety and atmospheric propagation through obscurants. NVESD has several active programs in this area, which will be reviewed in this paper. These are: 1) single-pixel scanned imaging laser radar, 2) 2D gated SWIR imaging, and 3) 3D-flash laser radar. These systems are being evaluated for various targeting scenarios, including as potential payloads on unmanned air-vehicles, ground vehicles and other sensor suites. Applications include low-cost long-range target identification, identification of heavily obscured targets, obstacle avoidance, and high resolution imaging.

BAE SYSTEMS has developed a Low Cost Targeting System (LCTS) consisting of a FLIR for target detection, laser-illuminated, gated imaging for target identification, laser rangefinder and designator, GPS positioning, and auto-tracking capability within a small compact system size. The system is based upon BAE Systems proven micro-bolometer passive LWIR camera coupled with Intevac's new EBAPS camera. A dual wavelength diode pumped laser provides eyesafe ranging and target illumination, as well as designation; a custom detector module senses the return pulse for target ranging and to set the range gates for the gated camera. Trials show that the current detectors offer complete extinction of signals outside of the gated range, thus, providing high resolution within the gated region. The images have shown high spatial resolution arising from the use of solid state focal plane array technology. Imagery has been collected in both the laboratory and the field to verify system performance during a variety of operating conditions.

3-D flash ladar, herein defined as obtaining an entire frame of 3-D ladar data with one laser pulse, is an emerging technology with a number of advantages over conventional point scanner systems. Probably the most obvious advantage is the higher data rates possible and the potential for much higher data rates with increases in the associated 3-D focal planes array (FPA) format. High data rate means that topographical mapping, for example, can be obtained more rapidly decreasing the amount of flight time required. This paper investigates the clear but perhaps not-so-intuitive use of the high data rate: time dependent 3-D movies can be acquired at the repetition frequency of the associated laser. Data is taken using 3-D flash ladar cameras fabricated by Advanced Scientific Concepts, Inc. The paper concludes that there are a number of advantages and unique applications of the time dynamic 3-D flash ladar, including 3-D collision avoidance and object tracking.

Since the distribution of anthrax causing spores through the U.S. Postal System in the autumn of 2001, bioterrorism has become an ever present threat. During and following an attack it is also important to detect spores on surfaces, to assess the extent of an attack, to quantify risk of infection by contact, as well as to evaluate post-attack clean-up. To perform useful measurements, analyzers and/or methods must be capable of detecting as few as 10 spores/cm², in under 5-minutes, with little or no sample preparation or false-positive responses, using a portable device. In an effort to develop such a device, we have been investigating the ability of surface-enhanced Raman spectroscopy (SERS) to detect dipicolinic acid (DPA) as a chemical signature of bacilli spores. In general, SERS is capable of detecting mg/L concentrations and lower, and providing unequivocal identification of chemicals based on each one's unique spectrum. However, rapid analysis requires extracting the DPA from the spores for SERS detection. Here we describe the use of a room temperature digesting agent in combination with SERS to detect 220 spores on a surface, the entire procedure which was performed in 2.5 minutes.

Infrared spectroscopy has been demonstrated as a powerful tool for taxonomic classification of bacteria when the microbes are grown and sampled under carefully controlled conditions. Infrared spectroscopy affords limited information about relative proportions of certain chemical functional groups in whole microbial cells. The objective of this work is to elucidate the ability of infrared spectroscopy to identify and speciate Bacillus spp. regardless of sample history. Spectrometers utilize different scanning methods to collect infrared absorption spectra. We employed three; transmission through a thin film, transmission infrared microscopy, and Attenuated Total Reflection (ATR). Target organisms include Bacillus anthracis, and several near neighbors. Each strain was cultured at 24°C and 35°C on three solid media. Microorganisms were incubated for up to ten days to include vegetative cells, spore formation and mature spores. Triplicate microbe samples were prepared and analyzed according to instrument requirements using the three measurement modes. Triplicate samples of BSL-3 organisms were analyzed only by the thin film transmission method. Spectral data was analyzed using the cluster analysis function of OPUS software. We report that infrared spectrometry is capable of discerning Bacillus spores from vegetative cells and the phylogenic clustering of Bacillus species according to pathogenicity levels via infrared spectral analysis.

The stand-off detection classification by laser induced fluorescence is the objective of the Biosense project. The sensor will perform the monitoring of a defined area around its location using an elastic lidar detector for particles cloud. The detection of cloud will trigger fluorescence probing of the cloud. To perform this task the area fluorescence background will be monitored in order to evaluate if a return signal changed. Using a simple signal model built with experimental data, we designed a detection and monitoring procedure for the fluorescence at a single location. Signal simulations have been performed to verify the operation of the system. The results of the simulation indicate the system is able to detect anomaly with small contrast between a signal and the background. The results will have to be extended to area surveillance and a more complete signal model for various environments in natural conditions is required

We investigate the use of multiple scattering via Multiple-Field-Of-View (MFOV) lidar signals to characterize bioaerosol particles size and concentration from ground based lidar over distances shorter than a few kilometers. The MFOV lidar signal is calculated for background aerosols at a wavelength 355 nm for a visibility of 30 km. The optical depths studied are small and the calculations are restricted to second order scattering. Also since background aerosols are constituted of relatively small particles which diffuse the light at large angles, the fields of view (FOV) range from 1 to 100 mrad full angle. We show that the MFOV lidar measurements contain exploitable information on particle size and extinction.

In this paper, the passive standoff long wave infrared technology developed for atmospheric remote sensing was used to detect and identify chemical pollutants in the atmosphere. The measurement approach is based on the differential passive standoff detection method that has been developed by DRDC Valcartier during the past few years. The measurements were performed on real chemical warfare agents and toxic chemical vapors. The results clearly demonstrate the capability of the differential radiometry approach for the detection, identification and quantification of toxic chemical vapor clouds in an open-air environment.

Pixel Purity Index (PPI) has been widely used for endmember extraction. Recently, an approach using blocks of skewers was proposed by Theiler et al., called blocks of skewers (BOS) method, to improve computation of the PPI. It utilizes a block of skewers to reduce number of calculations of dot products operated by the PPI on each skewers with all data sample vectors. Unfortunately, the BOS method also suffers from the same drawbacks that the PPI does in terms of several parameters which are needed to be determined a priori. Besides, it also has an additional parameter, block size, B needed to be determined where no guideline is provided of how to select this parameter. In this paper, the BOS method is also investigated. Most importantly, a new pyramid-based block design for the BOS method is also introduced as opposed to the cube-based block designed used by Theiler et al.'s BOS. One major advantage of our proposed pyramid-based BOS over Theiler et al.'s cube-design BOS is the hardware design for Field Programmable Gate Arrays (FPGAs) implementation.

A compact high peak power eye-safer optical parametric oscillator was constructed by pumping it with a master oscillator power amplifier consisting of a large-mode-area ytterbium doped fiber amplifier and a diode-pumped, passively Q-switched Nd:YAG microchip laser. The master oscillator power amplifier has the maximum output pulse energy of 570 μJ with a 3 nanosecond pulse width and a 3 kHz pulse repetition rate. The compact singly resonating optical parametric oscillator utilized a 50 mm periodically poled Lithium Niobate crystal and generated high peak power 1.5 μm eye-safe laser pulses with more than 140 μJ pulse energy, 3 nanosecond pulse width and 3 kHz repetition rate.