A general approach to the evaluation of remote chemical sensors is described that can be used to provide evaluation of the chemical detection in a particular chemical scenario. It will be used to make comparisons of a CO₂ laser differential absorption lidar sensor and a passive thermal FTIR sensor. The focus of the study will be to evaluate the advantage of the FTIR sensor's spectral coverage and number of frequency channels.

This paper presents preliminary results on the effects of spectral resolution and atmospheric transmission on the recovery of species concentrations using Partial Least Squares procedures. The effects of different levels of random spectral noise on the recovery of concentrations are also explored. Calculations were limited to absorbance spectra, however, future effort is to be directed to more realistic passive sensing cases where radiative-transfer effects are taken into account.

Radiometric models have been used to optimize instrument design or evaluate impacts of changes to the design during integration and test. Tradeoffs such as spectral and spatial resolution, telescope and spectrometer temperature, aperture, f/No., integration time, optics and filter transmissions, and so forth can be quickly changed to evaluate changes to the signal/noise ratio or other performance metrics. An alternative use of such models is to identify promising instrument proposals for further study. A series of models were constructed to evaluate general instrument designs as an illustration of this process. These models included two grating spectrometers and a spatially modulated interferometer. All were given a common set of radiometric inputs and telescope optical prescription. Result of the modeling illustrate the performance differences between instrument types, although signal/noise predictions should be evaluated along with other parameters such as manufacturability, precision of calibration, and so forth. Such modeling allows instrument developers to demonstrate to potential customers improvements in their instruments, and the advantages of their product over other instruments for a specific application. If a common set of inputs is used for the different instrument models, this technique gives customers one metric with which to evaluate the disparate proposals.

The sensitivity of spectroscopic detection of low-lying gas clouds by an arbitrary spectrometer may be determined by simulating the observation using a high spectral resolution radiative transfer code. The instrumental characteristics may be superimposed on the simulation and the accuracy of the retrieval of the desired parameters may be estimated by use of the covariance matrix.

An apparatus has been designed and constructed to continuously monitor the number density, size, and fluorescent emission of ambient aerosol particles. The application of fluorescence to biological particles suspended in the atmosphere requires laser excitation in the UV spectral region. In this study, a Nd:YAG laser is quadrupled to provide a 266 nm wavelength to excite emission from single micrometer-sized particles in air. Fluorescent emission is used to continuously identify aerosol particles of biological origin. For calibration, biological samples of Bacillus subtilis spores and vegetative cells, Esherichia coli, Bacillus thuringiensis and Erwinia herbicola vegetative cells were prepared as suspensions in water and nebulized to produce aerosols. Detection of single aerosol particles, provides elastic scattering response as well as fluorescent emission in two spectral bands simultaneously. Our efforts have focuses on empirical characterization of the emission and scattering characteristics of various bacterial samples to determine the feasibility of optical discrimination between different cell types. Preliminary spectroscopic evidence suggest that different samples can be distinguished as separate bio-aerosol groups. In addition to controlled sample results, we will also discuss the most recent result on the effectiveness of detection outdoor releases and variations in environmental backgrounds.

In recent history, manmade and natural events have shown us the every-present need for systems to monitor the troposphere for contaminates. These contaminants may take either a chemical or biological form, which determines the methods we use to monitor them. Monitoring the troposphere for biological contaminants is of particular interest to my organization. Whether manmade or natural, contaminants of a biological origin share similar constituents; typically the aromatic amino acids tryptophan, phenylalanine, and tyrosine. All of these proteinaceous compounds autofluorescence when exposed to UV radiation and this established the basis of the laser-induced fluorescence technique we use to detect biological contaminants. This technique can be employed in either point or remote detection schemes and is a valuable tool for discriminating proteinaceous form non-proteinaceous aerosols. For this particular presentation I am going to describe a breadboard point sensor we designed and fabricated to detect proteinaceous aerosols. Previous point sensor designs relied on convoluted flow paths to concentrate the aerosols into a solution. Other systems required precise beam alignment to evenly distribute the energy irradiating the detector elements. Our objective was to build a simple system where beam alignment is not critical, and the flow is straight and laminar. The breadboard system was developed over a nine- month period and its performance assessed at a recent test at Dugway Proving Grounds in Utah. In addition, we have performed chamber experiments in an attempt to establish a baseline for the systems. The results of these efforts are presented here.

Our group has been developing a system for single-particle fluorescence detection of aerosolized agents. This paper describes the most recent steps in the evolution of this system. The effects of fluorophore concentrations, droplet size, and excitation power have also been investigated with microdroplets containing tryptophan in water to determine the effects of these parameters on our previous results. The vibrating orifice droplet generator was chosen for this study base don its ability to generate particles of well- known and reproducible size. The power levels required to reach saturation and photodegradation were determined. In addition, the collection of fluorescence emission was optimized through the use of a UV achromatic photographic lens. This arrangement permitted collection of images of the droplet stream. Finally, the use of a dual-beam, conditional firing scheme facilitated the collection of improved signal- to-noise single-shot spectra from individual biological particles.

The detection and characterization of micro-particles, particularly airborne biological particles, is currently of great interest. We present a novel technique for recording the 2D angular scattering pattern from a single airborne microparticle. Angular scattering measurements were performed in both the near-forward and near-backward regions for a variety of particles including for ethanol droplets, single polystyrene latex spheres, psl clusters, and clusters of Bacillus subtilis spores, all of various sizes. Because the angular scattering pattern is sensitive to size, shape and refractive index, the angular feature associate with clusters may be used to better characterize such airborne micro-particles. A watershed image processing routine has also been implemented. Through this routine, the number of intensity patches per solid angles is found to increase with cluster diameter.

The presented system is based upon a differential imaging radiometry technique, differential in both spectral and spatial domains: The observation of a scene, acting as an IR complex source is realized through a set of wide band filters: 1) a 'reference' filter, the transmission of which is located outside the absorption features of the gas of interest: the resulting picture characterizes the scene background. 2) A 'measure' filter, the transmission of which includes the absorption or emission bands of the gas of interest while remaining as close as possible to the 'reference' filter. The use of such filters, characterized by a high IR transmission over a wide wavelength band unlike the conventional radiometric methods, preserves the imaging function of the thermal imager. A specific treatment is applied to the resulting pictures. Its originality consists in that gas concentration is not directly computed from the received IR flux, but from the image contrast variations between the two filtered images. In this way, the emission flux of gas cloud can be eliminated. Finally, the comparison of the 'contrast' images gives an absolute and quantitative measurement of gas concentration of the cloud integrated along the line of sight, whatever the respective temperatures of the gas cloud and the background scene are. A first generation demonstrator base don 8-12 micrometers commercial radiometric camera, and integrating a quasi-real time processing software, was tested on several chemical agents, both in closed chamber and in open field. This paper presents an overview of the measurement technique and gas cloud evolution experiments in urban atmosphere.

Physical Sciences Inc. (PSI) has developed an Adaptive IR Imaging Spectroradiometer, comprised of a low-order tunable Fabry-Perot etalon coupled to an HgCdTe detector array, for passive, stand-off detection of chemical vapor plumes. The tunable etalon allows coverage of the 9.5 to 14 micrometers spectral region with a resolution of approximately 7 cm^-1 and provides the capability to obtain monochromatic images of a scene at only those wavelengths needed for chemical species identification and quantification. The adaptive sampling capability of the etalon allows suppression of background clutter and minimization of data volume. The tuning time between transmission wavelengths is typically approximately 10 ms, however the mirror tuning system may be operated to obtain tuning times as short as 1.3 ms. We present results using a brassboard imaging system for stand-off detection and visualization of chemical vapor plumes against near ambient temperature backgrounds. This data shows detections limits of 22 ppmv m and 0.6 ppmv m for DMMP and SF₆ respectively against a (Delta) T of 6 K. The reported detection limits are consistent with the measured system noise-equivalent spectral radiance, approximately 2 (mu) W cm^-2 sr^-1 micrometers ^-1.

Advanced autonomous detection of chemical warfare agents and other organic materials has long been a major military concern. While significant advances have recently been accomplished in remote spectral sensing using rugged FTIRs with point detectors, efforts towards spatial chemical discrimination have been lacking. Foster-Miller, Inc. has developed a radically different mid-IR and long wave IR spectrometer for standoff detection of chemical warfare agents and other molecular species.This no moving parts device will eliminate the cost, complexity, reliability and bandwidth/resolution problems associated with either Fabry Perot or Michelson Interferometer based approaches currently under consideration. Given the small size and performance insensitivity to on-board vibration, high EMI, thermal variations, the proposed optic would easily adapt cryocooling and field deployable requirements for low radiance detection.

The US Army is currently developing a Chemical Imaging Sensor for the wide-area detection and identification of chemical warfare agents. As part of this effort, LWIR multispectral imaging data was collected with the Adaptive Infrared Imaging Spectroradiometer. Laboratory experiments were conducted using chemical agent simulants, including DMMP and DIMP at different vapor concentration levels. The resulting 14-band images were analyzed by a least squares approach as well as by Convex Cone Analysis (CCA). Both analyses demonstrate the potential of multispectral chemical imaging for wide-area standoff detection. In addition, it is shown that CCA is capable of detecting the presence of spectrally active chemical vapors and estimating their absorbance spectrum without any prior knowledge about the presence or composition of the chemical vapors.

Fourier-transform microwave (FTMW) spectroscopy is an established is an established technique for observing the rotational spectra of molecules and complexes in molecular beams. Scientists at the National Institute of Standards and Technology (NIST) are adapting this measurement technology for applications in analytical chemistry. Presently, FTMW spectroscopy is being used to investigate chemical-warfare agents and their synthetic precursors. A FTMW spectroscopy facility has been established at a surety laboratory at the Edgewood Research, Development, and Engineering Center, where the capabilities exist for handling these deadly warfare agents. Here, the rotational spectra of Sarin, Soman and DF have been observed and assigned. Also, microwave spectroscopic studies of less toxic precursors such as pinacolyl alcohol, isopropyl alcohol, and thiodiglycol have been carried out at NIST. Tests will be undertaken to assess the potential of using FTMW spectroscopy for detecting trace amounts of chemical-warfare agents and precursors in air. A database of rotational transition frequencies is being compiled for use in conjunction with a FTMW spectrometer to unambiguously detect and monitor chemical weapons. The sensitivity and resolution of FTMW spectroscopy of FTMW spectroscopy suggest that the technique may offer real-time, unequivocal identification of chemical-warfare agents at trace vapor concentrations in air.

A small business innovation research Phase II program is being conducted for the US Naval Air Warfare Center - Aircraft Division at Patuxent River, Maryland. The goal is to develop a chemical agent standoff and point detection systems (CASOPDS). The CASOPDS is comprised of standoff and point detection subsystems contained in a stand-alone transit case which can be transported to, carried on-board, and readily installed in the V-22 Osprey aircraft in the event of a CW threat.

This paper extends an earlier optimal approach for frequency-agile lidar using fixed-size samples of data to include the time series aspect of data collection. The likelihood ratio test methodology for deterministic but unknown vapor concentration is replaced by a Bayesian formalism in which the path integral of vapor concentration CL evolves in time through a random walk model. The fixed- sample maximum likelihood estimates of CL derived earlier are replaced by Kalman filter estimates, and the log- likelihood ratio is generalized to a sequential test statistic written in terms of the Kalman estimates. In addition to the time series aspect, the earlier approach is generalized by (1) including the transmitted energy on a short-by-shot basis in a statistically optimum manner, (2) adding a linear slope component to the transmitter and received data models, and (3) replacing the nominal multivariate normal statistical assumption by a robust model in the Huber sensor for mitigating the effects of occasional data spikes caused by laser misfiring or EMI. The estimation and detection algorithms are compared with fixed-sample processing by the DIAL method on FAL data collected by ERDEC during vapor chamber testing at Dugway, Utah.

This paper discusses the development of a frequency agile receiver for CO₂ laser based differential absorption lidar (DIAL) systems. The receiver is based on the insertion of a low-order tunable etalon into the detector field of view. The incorporation of the etalon in the receiver reduces system noise by decreasing the instantaneous spectral bandwidth of the IR detector to a narrow wavelength range centered on the transmitted CO₂ laser line, thereby improving the overall D* of the detection system. A consideration of overall lidar system performance result in a projected factor of 2 to 7 reduction in detector system noise, depending on the characteristics of the environment being probed. These improvements can play a key role in extending the ability of DIAL to monitor chemical releases form long standoff distances.

The sensor is a hybrid IR/UV lidar system that maps aerosol clouds, measures cloud wind speed and direction, and determines whether the cloud fluoresces. It is being developed by EOO, Inc. and SRI International under a DARPA SBIR. The hybrid IR/UV lidar system was conceived to operate from a small UAV platform for tactical battlefield missions. The IR sensor can detect and map aerosol clouds out to ranges of several kilometers. After detection, the UAV can close to within several hundred meters of the cloud and interrogate it with the UV sensor to identify whether the UV cloud fluoresces. Both sensors use the same basic IR laser source that is non-linearly shifted to the appropriate UV wavelength. The IR sensor also provides wind speed using edge-filter Doppler information. Parametric studies during the Phase I SBIR provided performance vs. form/fit trade-off for various platforms. The tactical UAV was chosen as the platform to guide the Phase II brassboard development. Other airborne and ground-based platforms suitable for surveillance or intelligence can be used. The paper will describe the brassboard system and the sensor performance as validated by test data.

We describe the development of an IR source capable of generating light simultaneously in the 3-4 micrometers and 8-13 micrometers bands. Using a tandem optical parametric oscillator architecture, the output wavelengths arise as the signal and idler, respectively, of an AgGaSe₂ based OPO. Both efficiency and tuning of this OPO system are discussed and, in particular, a rapid electrooptic method of tuning both mid-wave and long wave IR bands is described.

Effective remote sensing DIAL transmitters require accurate and rapid monitoring of their wavelength and spectral linewidth. For mid-wave and long-wave IR transmitters, an absolute measurement resolution on the order of 0.1 cm^-1 allows for accurate turning of the source onto narrow absorption lines of atmospheric molecules. Unfortunately, pulsed wavemeters with this level of resolution, that also operate outside of the visible and near IR regions, are not readily available. We have, therefore, designed and constructed a suitable spectral diagnostic instrument for use with an optical parametric oscillator-based DIAL transmitter. The transmitter is capable of emitting simultaneously in the 3-4 micron and 8- 13 micron regions. Although the operating wavelength range of the wavemeter is restricted to 1.4-1.85 microns, relationships between pump, signal and idler wavelengths, along with a nonlinear frequency mixing technique, allow the wavemeter to serve as a complete spectral diagnostic for this broadband transmitter. The wavemeter architecture is based on a combination grating spectrograph and single-stage Fabry-Perot etalon design.

The purpose of this project is to build a prototype instrument that will, running unattended, detect, identify, and quantify BW agents. In order to accomplish this, we have chosen to start with the world's leading, proven assays for pathogens: surface-molecular recognition assays, such as antibody-based assays, implemented on a high-performance, identification (ID)-capable flow cytometer, and the polymerase chain reaction for nucleic-acid based assays. With these assays, we must integrate the capability to: (1) collect samples form aerosols, water, or surface; (2) perform sample preparation prior to the assays; (3) incubate the prepared samples, if necessary, for a period of time; (4) transport the prepared, incubated samples to the assays; (5) perform the assays; (6) interpret and report the result of the assays. Issues such as reliability, sensitivity and accuracy, quantify of consumables, maintenance schedule, etc. must be addressed satisfactorily to the end user. The highest possible sensitivity and specificity of the assay must be combined with no false alarms. Today, we have assays that can, in under 30 minutes, detect and identify simulants for BW agents at concentrations of a few hundred colony- forming units per ml of solution. If the bio-aerosol sampler of this system collects 1000 1/min and concentrates the respirable particles into 1 ml of solution with 70 percent processing efficiency over a period of 5 minutes, then this translates to a detection/ID capability of under 0.1 agent- containing particle/liter of air.

Recently, a number of analytical methods have been successfully developed which use nucleic acid sequencing to identify biological warfare agents. However, the effectiveness of these methods, towards the safety and protection of US Armed Forces and their allies are limited by the period required to enumerate the nucleic acid through polymerase chain reactions or culture growth to produce sufficient quantities for analysis. To overcome this limitation, we have been investigating the ability of surface-enhanced Raman spectroscopy to detect nucleic acids with sufficient sensitivity and selectivity to eliminate the need for enumeration. The design of a small volume electrolytic sample cell will be presented along with analysis of the nucleic acid bases and preliminary analysis of model bacteria.

Polymerase Chain Reaction (PCR) is an in vitro enzymatic, synthetic method used to amplify specific DNA sequences from organisms. Detection of DNA using gene probes allows for absolute identification not only of specific organisms, but also of genetic material in recombinant organisms. PCR is an exquisite biological method for detecting bacteria in aerosol samples. A major challenge facing detection of DNA from field samples is that they are almost sure to contain impurities, especially impurities that inhibit amplification through PCR. DNA is being extracted from air, sewage/stool samples, food, sputum, a water and sediment; however, multi- step, time consuming methods are required to isolate the DNA from the surrounding contamination. This research focuses on developing a method for rapid cleanup of DNA which combines extraction and purification of DNA while, at the same time, removing inhibitors from 'dirty samples' to produce purified, PCR-ready DNA. GeneReleaser produces PCR-ready DNA in a rapid five-minute protocol. GeneReleaser resin was able to clean up sample contain micrograms of typical aerosol and water contaminants. The advantages of using GR are that it is rapid, inexpensive, requires one-step, uses no hazardous material and produces PCR-ready DNA.

Sensitivity and selectivity requirements in on-line trace gas analysis of volatile organic compounds often cannot be satisfied. Due to their photochemical Ozone creation potential there is a strong demand for fast and accurate measurement techniques. Although many spectroscopy techniques are quite sensitive to individual components they often suffer from a lack of selectivity between similar spectroscopic compounds. We report on a special system with optical derivative generation. Gas analysis is performed by means of transmission spectroscopy in the UV. A deuterium lamp is used as light source. Due to the strong UV- absorption bands of organic compounds, sensitive detection is typical. Spectroscopic filtering is provided by a special grating monochromator. The grating is mounted on a galvanometer scanner, allowing a computer controlled wavelength scan and modulation. Analog signal processing is performed using lock-in-amplifier techniques. This form of detection of derivative spectra with a movable optical component is the origin of the term Dynamic Derivative Spectroscopy (DDS). Combined with the use of a White-Cell - providing an optical path length up to 100m - very high sensitivity is achieve. The adjustment of the wavelength- modulation amplitude, as a significant parameter of DDS, can be optimized to the gas of interest due to the individual and characteristic slopes and curvatures of the gaseous absorption bands. Selectivity is improved separating spectral features in overlapping bands. We discuss the theoretical background and present experimental data on system performance. The impact of wavelength modulation as a powerful tool is demonstrated, sensitive and fast multicomponent measurements of volatile organic compounds are presented.

We present a novel method, the Gas Imaging (GIm) method, developed for the localization of gas distributions in the atmosphere. The method is suitable for the detection of a gases which exhibit at least one absorption line in the IR spectral range. In this paper the GIm method is demonstrated for methane released into the atmosphere from leaks along natural gas pipelines. Methane distributions in the atmosphere around the leaky pipeline are detected and visualized by spectrally tuned IR imaging. In contrast to conventional techniques which utilize laser radiation sources or scanning, we irradiate the overall region under investigation by 1 kW halogen lamps. The scene background is subtracted by a real-time computer evaluation of the image. The methane gas emitted from the leak creates a flickering cloud in the image which is easily recognized. Methane concentrations as low as 0.03 percent by volume are visible. The method was successfully tested under realistic conditions on a buried pipeline by a natural gas provider.

The lidar remote sensing techniques are powerful for monitoring of gaseous toxic species in atmosphere over wide areas. The paper presented describes design, development and field testing of Mobile Lidar System (MLS) based on utilization of Differential Absorption Lidar (DIAL) technique. The activity is performed by Russian Research Center 'Kurchatov Institute' and Research Institute of Pulse Technique within the project 'Mobile Remote SEnsing System Based on Tunable Laser Transmitter for Environmental Monitoring' under funding of International Scientific and Technology Center Moscow. A brief description of MLS is presented including narrowband transmitter, receiver, system steering, data acquisition subsystem and software. MLS is housed in a mobile truck and is able to provide 3D mapping of gaseous species. Sulfur dioxide and elemental mercury were chosen as basic atmospheric pollutants for field test of MLS. The problem of anthropogenic ozone detection attracts attention due to increase traffic in Moscow. The experimental sites for field testing are located in Moscow Region. Examples of field DIAL measurements will be presented. Application of remote sensing to toxic species near-real time measurements is now under consideration. The objective is comparison of pollution level in working zone with maximum permissible concentration of hazardous pollutant.

It is known that the tunable diode laser spectroscopy provides a very high degree of selectivity and sensitivity of the detection of gaseous components. For the evaluation of the mean density of a specific molecular constituent, the differential absorption method is employed. Recently it was shown that probing by a frequency-modulated single sideband signal and measuring the resulting radio-frequency beat signal phase relates absorption and dispersion and provides a species detection limit well below 1 part per billion if a multiple-pass cell is used. More recently it was shown that the dispersive properties near to the absorption lines of a matter can be used for concentration measurements. Now the theoretical research is showing that the nonlinearity of the refractive index near an absorption and more workable than the beat phase. The short pulse laser promotes excellent temporal and spatial resolution of pollutant detecting and analysis. This idea may also be used for the laser remote sensing by short pulses.

A standoff detection of atmospheric tracer dispersion in a military installation, using active and passive remote sensors, was demonstrated in a field test. System performance was evaluated at various atmospheric conditions, different forms of tracer release and different rates of release. Source locations as well as sensors positions were varied between test. A network of point detectors was used as an additional mean to map tracer concentrations, especially at locations not accessed by the remote sensors due to the complex nature of the installation.The test results are presently in a process of evaluation, some of them are presented here.

Dipicolinic acid (DPA) and the Ca²⁺ complex of DPA (CaDPA) are well-known and are major chemical components of bacterial spores. DPA's native fluorescence is very weak and is thought to be completely masked by the fluorescence of tryptophan when this compound is presented. Thus fluorescence related to DPA in spores is assumed by many authors to be completely absent. AWe show that the fluorescence of CaDPA is substantial for excitation between about 290 nm and 310 nm with emission peaking near 400 nm. This emission is at the long wavelength tail for emission form tryptophan. We examine whether the emission of CaDPA could contribute to the total emission spectrum when bacterial spores are present in an aerosol, for excitation wavelength in the neighborhood of 310 nm. In this report we present measurements of fluorescence excitation and emission for CaDPA and compare them with that of DPA and tryptophan.