This paper describes the Chemical Cloud Tracking System (CCTS) which has been installed at Dugway Proving Ground. The CCTS allows mapping of chemical clouds in real time from a safe standoff distance. The instruments used are passive standoff chemical agent detectors (FTIRs). Each instrument individually can only measure the total of all the chemical in its line-of-site; the distance to the cloud is unknown. By merging data from multiple vantage points (either one instrument moving past the cloud or two or more instruments spaced so as to view the cloud from different directions) a map of the cloud locations can be generated using tomography. To improve the sensitivity and accuracy of the cloud map, chemical point sensors can be added to the sensor array being used. The equipment required for the CCTS is commercially available. Also, the data fusion techniques (tomography) have been demonstrated previously in the medical field. The Chemical Cloud Tracking System can monitor the movement of many chemical clouds of either military or industrial origin. Since the technique is standoff, the personnel are not exposed to toxic hazards while they follow the cloud. Also, the equipment works on-the-move which allows rapid response to emergency situations (plant explosions, tanker car accidents, chemical terrorism, etc.).

A Virtual Proving Ground (VPG) for evaluation of CB detectors is being developed by the U.S. Army at Dugway Proving Ground (DPG). The VPG is essentially a combination of computer models for the scene and a detector. The objective is to evaluate the detector performance without requiring expensive field tests. To support the VPG, a general purpose, passive standoff detector model was developed using models from the literature. The important environmental stress variables that affect the detector output signal are determined using 2 level factorial design experiments. An example 2 level factorial design experiment with ILSCAD data is discussed. The model parameters are determined with various detector characterization tests. These include spatial responsivity measurement, wavenumber scale calibration, line shape function measurement, and spectral response measurement. An overview of the detector model and the characterization procedures is discussed.

The HiSPEC instrument was designed to examine the potential for passive detection of sub-lethal concentrations of toxic materials and to test the potential for passive indication of biological agent in air. HiSPEC has been operating since 1999, and after substantial laboratory characterization, taken to the field several times for successful trials against known remote targets. Some subtle differences between laboratory and field performance have been diagnosed for the first time with the aid of HiSPEC's precise internal sampling system. Results of these tests may have implications for improving less sensitive passive field systems. Some recent field data is presented to indicate ultimate potential.

An experimental and modeling study performed to estimate the spectral radiance of surface contaminants is presented. The goal of the study is to address issues relevant to the passive standoff detection of surface contaminants. For this experiment, SF96 and Krylon 41325 are used as contaminant simulants and the contamination of four different surfaces (aluminum, grass, soil and plywood) is analyzed. A first order model of reflectance for surface contaminants is proposed. Measurements of spectral radiance with the CATSI system is compared with the best-fit spectra derived from the model. The experimental results agree well with the model best fits for Krylon on aluminum and grass samples. For Krylon on soil and SF96 on plywood the model best fits fail to reproduce the experimental spectra. The reasons for this discrepancy is discussed.

Advanced autonomous detection of both chemical warfare agents and toxic industrial chemicals has long been of major military concern and is becoming an increasingly realistic need. Foster-Miller has successfully designed and demonstrated a high spectral throughput monolithic wedge spectrometer capable of providing early, stand-off detection of chemical threats. Recent breakthrough innovations in IR source technologies, high D* multispectral array detectors, and IR waveguide materials has allowed for the development of a robust, miniature, monolithic infrared spectrometer. Foster-Miller recently demonstrated a high resolution spectrometer operating in the 8 to 12 micron region for chemical agent detection. Results will be presented demonstrating the feasibility of adapting the wedge spectrometer to operate as an upward looking ground sensor for stand-off chemical detection. Our miniaturized spectrometer forms the basis for deploying low cost, lightweight sensors which may be used for reconnaissance missions or delivered to remote locations for unattended operation. The ability of perform passive stand-off infrared chemical agent and chemical emissions detection with a low cost, compact device that can operate autonomously in remote environments has broad applications in both the military and commercial marketplace.

A new technique for measuring air pollutants in the lower part of the troposphere has been developed. The technique is based on Fourier-transform infrared (FTIR) spectroscopy, which is used to measure the atmospheric thermal emission from gases beneath uniform cloud cover. The cloud acts as a cold background emission source against which the emission from gases in the warmer atmosphere beneath the cloud may be detected. The region of the infrared spectrum near 2400 cm^-1, which is nearly void of significant atmospheric water vapour emission, is used to infer the cloud base temperature. The FASCOD3 atmospheric transmission code is used to simulate the background emission spectrum below the cloud, which is then subtracted from the measured spectrum to yield the thermal emission band of a particular gas. Based on the band intensity, the average concentration of the gas in the lower atmosphere may be determined. In order to have sufficient detection sensitivity, the cloud base must exceed an altitude of about 1 km. The gases that have been successfully measured with this technique include tropospheric ozone, carbon dioxide, carbon monoxide and nitrous oxide. By comparing the tropospheric ozone amounts to the surface amounts measured with an ozone analyser over the past two summers, it was discovered that the ozone residing in the lower troposphere sometimes has a concentration that is nearly twice the value recorded at the surface. This result has important implications concerning air pollution models, which normally incorporate ozone amounts from meteorological stations at the surface.

The Chemical Imaging System (CIS) is a small, high-speed long-wave infrared (8 - 12 micrometers ) imaging spectrometer which is currently under development by the United States Army. The fielded system will operate at 360 scans per second with a large format focal-plane-array. Currently, the CIS uses the TurboFT FTS in conjunction with a 16-pixel direct-wired HgCdTe detector array. The TurboFT spectrometer provides high-speed operation in a small, lightweight package. In parallel to the hardware development, an algorithm and software development effort is underway to address some unique features of the CIS. The TurboFT-based system requires a non-uniform sampling Fourier transform algorithm in order to preserve signal fidelity. Also, the availability of multiple pixels can be exploited in order to improve the interference suppression capabilities of the system by allowing the detection and identification algorithm to adapt its parameters to the changing background. Due to the enormous amount of data generated, the signal processing must proceed at very high rate. High-speed computers operating with a parallel architecture are required to process the data in real time. This paper describes the current CIS bread box system. It includes some field measurement results followed by a discussion of the issues and challenges associated with meeting the design goals set for the program.

Physical Sciences Inc. has developed and tested two long-wavelength infrared (LWIR) hyperspectral imaging spectroradiometers based on the insertion of a rapidly tunable Fabry-Perot etalon in the field of view of a HgCdTe focal plane array (FPA). The tunable etalon-based optical system enables a wide field-of-view and the acquisition of narrowband (7 to 11 cm^-1 spectral resolution), radiometrically calibrated imagery throughout the 8 to 11 micrometers spectral region. The instruments function as chemical imaging sensors by comparing the spectrum of each pixel in the scene with reference spectra of target chemical species. We present results of recent field tests in this paper.

Under a NASA Stennis Space Center (SSC) SBIR, technologies required for an imaging spectral radiometer with wavenumber spectral resolution and milliradian spatial resolution that operates over the 8 micrometers to 12 micrometers (LWIR), and 3 micrometers to 5 micrometers (MWIR) bands, for use in a non-intrusive monitoring static rocket firing application are being investigated. The research is based on a spatially modulated Fourier transform spectral imager to take advantage of the inherent benefits in these devices in the MWIR and LWIR. The research verified optical techniques that could be merged with a Sagnac interferometer to create conceptual designs for an LWIR imaging spectrometer that has a 0.4 cm^-1 spectral resolution using an available HgCdTe detector. These same techniques produce an MWIR imaging spectrometer with 1.5 cm^-1 spectral resolution based on a commercial InSb array. Initial laboratory measurements indicate that the modeled spectral resolution is being met. Applications to environmental measurement applications under standard temperatures can be undertaken by taking advantage of several unique features of the Sagnac interferometer in being able to decouple the limiting aperature from the spectral resolution.

Remote sensing by Fourier-transform infrared (FTIR) spectrometry allows detection, identification, and quantification of airborne pollutants. In the case of leaks in pipelines or leaks in chemical plants, chemical accidents, terrorism, or war, hazardous compounds are often released into the atmosphere. Various Fourier-transform infrared spectrometers have been developed for the remote detection and identification of hazardous clouds. However, for the localization of a leak and a complete assessment of the situation in the case of the release of a hazardous cloud, information about the position and the size of a cloud is essential. Therefore, an imaging passive remote sensing system comprised of an interferometer (Bruker OPAG 22), a data acquisition, processing, and control system with a digital signal processor (FTIR DSP), an azimuth-elevation-scanning mirror, a video system with a DSP, and a personal computer has been developed. The FTIR DSP system controls the scanning mirror, collects the interferograms, and performs the Fourier transformation. The spectra are transferred to a personal computer and analyzed by a real-time identification algorithm that does not require background spectra for the analysis. The results are visualized by a video image, overlaid by false color images. For each target compound of a spectral library, images of the coefficient of correlation, the signal to noise ratio, the brightness temperature of the background, the difference between the temperature of the ambient air and the brightness temperature of the background, and the noise equivalent column density are produced. The column densities of all directions in which a target compound has been identified may be retrieved by a nonlinear least squares fitting algorithm and an additional false color image is displayed. The system has a high selectivity, low noise equivalent spectral radiance, and it allows identification, visualization, and quantification of pollutant clouds.

A novel methodology has been developed for the determination (i.e., identification and quantification) of bacterial spores that may be useful in many applications; most notably, development of detection schemes toward potentially harmful biological agents such as Bacillus anthracis. In addition, this method would be useful as an environment warning system where sterility is of importance (i.e., food preparation areas as w ell as invasive and minimally- invasive medical applications). This method is based on the infrared (1500 to 4000-nm) absorption of fatty acids and peptides extracted from the spore. The absorption spectra of several bacteria spore extracts in carbon disulfide solution have been measured. Further, the groups of absorption bands in the this region are unique for each spore, which implies it may be possible to use this technique for their determination. The Bacillus spores studied were chosen because they are taxonomically close to each other as well as to Bacillus antracis. Expectedly, the measured absorption bands are heavily overlapped since the extracted analytes are similar in structure for each Bacillus spore. Additionally, this makes it impossible to use a single wavelength for the determination of any bacterial spore species. However, it may be possible to use the infrared absorption technique in conjunction with the Partial Least Squares (PLS) regression method to develop statistical models for the determination of bacterial spores. Results will be presented concerning sampling, data treatment, and development of PLS models as well as application of these models in the determination of unknown Bacillus bacterial spores.

To address the need for a fast and sensitive method for the detection of bacterial contamination in solutions, the use of Fourier-transform near infrared (FT-NIR) spectroscopy and multivariate pattern recognition techniques was evaluated. The complex cellular composition of bacteria yields FT-NIR vibrational transitions (overtone and combination bands) that might be useful for identification and sub-typing. Bacteria including strains of Escherichia coli spp., Pseudomonas aeruginosa, Bacillus spp. and Listeria innocua were evaluated. The harvested cells were treated with ethanol (70% v/v) to reduce the safety concerns when evaluating pathogenic strains. The bacterial cells were concentrated on an aluminum oxide membrane to obtain a thin bacterial film. Spectra were collected by FT-NIR by using a diffuse reflection-integrating sphere. This simple membrane filtration procedure generated reproducible FT-NIR spectra that can be used for rapid discrimination among closely related strains. Principal Component Analysis (PCA) of transformed spectra in the 5000-4000 cm^-1 region exhibited clusters that discriminated between bacteria species at levels < 1 mg wet cells weight (approximately 10⁶-10⁷ CFU/mg). Variations in the growth conditions of the bacteria substantially affected the FT-NIR spectra and diminished the ability of PCA to differentiate among strains; this underscores the importance of developing robust sampling protocols. FT-NIR in conjunction with multivariate techniques can be used for the rapid and accurate evaluation of potential bacterial contamination in liquids with minimal sample manipulation.

Low-frequency phonon modes of DNA and RNA molecules can serve as a signature of their structure, flexibility and, hence, their biological function. To investigate the relationship between RNA structure and far IR absorption spectra, we performed FTIR measurements on RNA molecules with known sequence in the spectral range from 10 cm^-1 to 25 cm^-1 and calculated their internal vibrations. To understand which phonon modes are determined by a double helical topology of nucleic acids, we compared the spectra of single stranded and double stranded RNA molecules. Homopolymers PolyA, polyU, polyC, and polyG, and double stranded homopolymers PolyA-polyU and polyC-polyG were investigated. Theoretical conformational analysis of the double stranded RNA molecules was performed and utilized to calculate the low-frequency vibrational modes. Conformational energy was minimized in the space of internal coordinates of a molecule using standard A-helical topology as an initial approximation. Normal modes were calculated as eigenfrequencies and eigenvectors of the matrix of energy second derivatives. Oscillator strengths were calculated for all the vibrational modes in order to evaluate their weight in the absorption spectrum of a molecule. The obtained phonon modes were convoluted to derive the far IR spectrum of a molecule. These predicted spectra were compared to those obtained by FTIR spectroscopy. Our results confirm that very far IR absorption spectra of biopolymers reflect specific dynamical properties resulting from their structure and topology and, therefore, can be used as fingerprints for specific molecules.

Experimental study on millimeter-wave absorption spectra from 180 to 220 GHz of biopolymers is presented in this paper. The proportional relation of absorbance with the density of the sample film is found out from the data set. Therefore, the technique of millimeter-wave absorption spectra is feasible for identification and early warning of biological agent.

We announce a new technique for the detection of changes in the conformation of small globular proteins in solution. We employ a coaxial-fed slot antenna with resonant frequencies in the 2-5 GHz range. This antenna detects changes in the dielectric properties of water. All proteins are surrounded by one or more shells of bound water. The dielectric properties of this 'bound' water are distinguishable from those of bulk water. As a protein changes it conformation, complementary changes occur in the three-dimensional arrangement of the 'bound' water. Thus, water can be used as a reporter for changes in protein conformation. Our technique has two advantages over conventional methods for microwave spectroscopy. First, unlike time-domain dielectric spectroscopy, data is measured in the frequency domain, so that time-to-frequency conversions are not necessary. Second, slot antennas may be affixed to the exterior of conventional fused-quartz cuvettes, so that simultane-ous measurements can be obtained using the antenna and conventional optical methods such as UV/VIS spectroscopy. When the unfolding of bovine pancreatic ribonuclease A (RNase A) is monitored at microwave frequencies, peak shifts in the antenna's resonant frequencies reflect changes in the protein's conformation. These peak shifts are sigmoidal with respect to temperature, and fit well to a two-state reversible unfolding model. Such sigmoidal peak shifts are not present when non-protein solutions are heated.

With support from the Department of Energy, the State of California and the Gas Technology Institute, Pacific Advanced Technology is developing a small field portable infrared imaging spectrometer (Sherlock) based on the advances in hyperspectral tunable filter technology, that will be applied to the detection of fugitive gas leaks. This imaging spectrometer uses the Image Multi-spectral Sensing (IMSS) diffractive optic tunable filter invented by Pacific Advanced Technology . The Sherlock has an embedded digital signal processor for real time detection of the gas leak while surrounded by severe background noise. The infrared sensor engine is a 256 x 320 midwave cooled focal plane array which spans the spectral range from 3 to 5 microns, ideal for most hydrocarbon leaks. The technology is by no means limited to this spectral region, and can just as easily work in the longwave infrared from 8 to 12 microns for chemical detection applications. This paper will present the design of the Sherlock camera as well as processed data collected at a gas processing plant and an instrumented kiln at LSU using the prototype camera. The processed data shows that the IMSS imaging spectrometer, using an all passive approach, has the sensitivity to detect methane gas leaks at short range with a flow rate as low as 0.01 scfm². In addition, the IMSS imaging spectrometer can measure hot gas plumes at longer ranges. As will be shown in this paper the IMSS can detect and image warm species gas additives of methane and propane in the Kiln exhaust stack. The methane injected gas with a concentration of 72 ppm and the propane with a concentration of 49 ppm (as seen by the IMSS sensor) at a range of 60 meters. The atmospheric path was a stressing environment, being hot and humid, for any imaging infrared spectrometer.

We present a new hyperspectral imaging system for the long wave infrared (LWIR) based on a tunable first-order Fabry-Perot Scanning Spectrometer (FPSS). The FPSS operates over 8 O 12 micrometers with a spectral resolution of 1% of the wavelength. The FPSS has a 22 degree field of view and a spatial resolution of 0.11 degrees. The key components of the FPSS system are the collection optics, a tunable Fabry-Perot etalon, optical position sensors, a closed-loop positioning system, an uncooled microbolometer focal plane array, a digital frame grabber card, and a user-friendly Graphical User Interface (GUI).

The paper presents results on research of tunable acousto-optic filters intended for operation in the ultraviolet region of spectrum at the wavelengths of radiation 220-480 nm. The goals of the investigation consisted in the confirmation of the possibility to apply the filters in outdoor monitoring of the Earth atmosphere. During the outdoor experiments, a precise and efficient filtration of direct solar radiation has been carried out by means of the coolinear quartz filter and the non-collinear KDP device. Detection and monitoring of temporary changes in the concentration of ozone in the atmospheric air has been carried out during the research.

Long-path spectral optical AOTF-based gas analyser is described. Comparison to other gas analyser operating on DOAS-principle is presented. Advantages of using AOTF as a spectral slective element are analysed. Results of instrument testing are listed.

Infrared absorption spectroscopy (IR) and acousto-optic tunable filter (AOTF) technology were combined to develop a portable spectrophotometer for use in engine oil analysis to identify and quantify oil contaminants and residue products, Preliminary measurements were taken with a field-portable AOTF-based spectrometer (2 to 4.5 micrometers ) and an FTIR spectrometer (2 to 25 micrometers ) for comparison. Absorption spectra of used and unused oil samples were measured and compared to determine absorption changes between the various samples resulting from oil degradation and any chemical reactions that might have taken place during high- temperature engine lubrication. These preliminary results indicate that IR spectroscopy can be used for oil quality monitoring in automotive engines, which will help predict and prevent engine failure and degradation. This work can be extended to other remote sensing applications, such as the monitoring of environmental oil spills.

We have developed relatively compact, lightweight, programmable hyperspectral/polarization imaging systems using an acousto-optic tunable filter with different focal plane arrays to cover the spectral range from the visible to the long infrared wavelength region. Four separate imagers have been developed to cover this spectral region. In general, an AOTF is a polarization-sensitive tunable optical device. By combining it with a tunable retarder we can also collect the polarization signatures as well as the spectral signatures. We have such spectropolarimetric imagers in the visible-to-near infrared (VNIR, 0.4-1.0 micrometers ) and short wave IR (SWIS, 0.9-1.7 micrometers ) regions. A lot of remote sensing data using a VNIR spectropolarimetric imager have been analyzed using a commercial image processing software program (ENVI). In this paper we will discuss the results of this analysis. The VNIR imager was used to collect spectral and polarization data from various objects and backgrounds, both in the laboratory and in field tests. This imager uses a tellurium dioxide (TeO₂) acousto-optic tunable filter (AOTF) and a liquid-crystal variable retardation (LCVR) plate with a charge coupled device (CCD) camera. The spectral images were collected from 0.45 to 1.0 micrometers with a 10 nm step, at two or four polarization settings for each spectral interval. We analyzed a portion of these data to assess the effectiveness of this system for foliage detection. Here we present our imager design, some results from our measurements and discuss the analysis results. Our results clearly show that compact, robust hyperspectral imaging systems with spectral and polarization detection capabilities will contribute significantly in a wide variety of future remote sensing applications.

MEMS silicon (Si) micro-bridge elements, with photonic band gap (PBG) modified surfaces are exploited for narrow-band spectral tuning in the infrared wavelength regime. Thermally isolated, uniformly heated single crystal Si micro-heaters would otherwise provide gray-body emission, in accordance with Planck's distribution function. The introduction of an artificial dielectric periodicity in the Si, with a surface, vapor-deposited gold (Au) metal film, governs the photonic frequency spectrum of permitted propagation, which then couples with surface plasmon states at the metal surface. Narrow band spectral tuning was accomplished through control of symmetry and lattice spacing of the PBG patterns. Transfer matrix calculations were used to model the frequency dependence of reflectance for several lattice spacings. Theoretical predictions that showed narrow-band reflectance at relevant wavelengths for gas sensing and detection were then compared to measured reflectance spectra from processed devices. Narrow band infrared emission was confirmed on both conductively heated and electrically driven devices.

Newly available mid-infrared lasers made from IV-VI compound semiconductors exhibit tuning ranges of over 200 cm^-1. In addition to allowing detection of a variety of species with a single laser, such wide tunability enables detection of large molecules with broad absorption bands. This paper presents results from detailed measurements of IV-VI diode laser emission obtained using an automated Fourier transform infrared (FTIR) spectroscopic testing system. Single mode emission wavelengths were determined for different combinations of heatsink temperature and injection current. These data were then used to design and perform molecular spectroscopy experiments in which laser emission wavelength was modulated by either current or temperature tuning. Current tuning over narrow spectral regions (up to 3 cm^-1) allowed detection of various small to medium sized molecules such as carbon disulfide, ammonium hydroxide, and benzene, but failed to detect larger molecules such as toluene. We show that temperature tuning a IV-VI laser over at least 50 cm^-1, however, can enable detection of large molecules such as toluene and improve the detection sensitivity of medium sized molecules such as benzene. This new technique extends the use of mid-infrared laser spectroscopy to measurement of large molecules that do not have resolvable ro-vibrational structure.

Quantitative multivariate spectroscopic methods seek spectral patterns that correspond to analyte concentrations even in the presence of interferents.By embedding a spectral pattern that corresponds to a target analyte in an interference filter in a beamsplitter arrangement;bulky and complex instrumentation can be eliminated with the goal of producing a field-portable instrument.A candidate filter design for an rganic analyte,of military interest,and an interferent is evaluated.

There is a continuing need for improved analytical techniques to measure the concentration of trace gases for monitoring hazardous air pollutants, industrial emissions, chemical-warfare agent release, etc. Methods of analysis that can conclusively identify several analytes in a mixture are particularly desired. Towards this end, the use of Fourier-transform microwave (FTMW) spectroscopy as a quantitative analytical technique has been proposed. The high spectral resolution of FTMW provides a quick and unambiguous method for identifying multiple analytes in the gas phase. A small-scale FTMW spectrometer has recently been constructed for use in quantitative analysis. Prior to the present investigation, however, the use of this spectrometer in quantitative work has not been rigorously evaluated. This work summarizes efforts to identify and categorize sources of signal instability in the FTMW spectrometer. Methods employed to minimize these effects will also be discussed.

The Pronghorn Field Tests were held at the Nevada Test Site for a two-week period in June 2001. Two passive infrared sensors were tested for inclusion into the Joint Service Wide Area Detection Program. The Adaptive InfraRed Imaging Spectroradiometer (AIRIS) and Compact ATmospheric Sounding Interferometer (CATSI) systems were tested with good results. This field test was a joint effort between the U.S (SBCCOM) and Canada (DREV). Various chemicals were detected and quantified from a distance of 1.5 kilometers. Passive ranging of Chemical Plumes was demonstrated.