A real time monitor, specifically designed to measure hydrogen fluoride (HF) concentration at the exit of the air purification system of aluminum smelters, has been tested and evaluated over a full year. The system has been designed to be rugged, with a low operating cost and easy to install and maintain in operation. These objectives have been achieved using a cheap halogen lamp as a light source, a simple micromotor as a light modulator, a pair of interference filters as optical analyzing elements and optical fibers as light guides between the central unit and the remote measurement points. In this application, the use of optical fiber provides two great advantages. Firstly, measurements in very demanding conditions become possible since the central unit, which has the task to make the entire optical electronic and digital processing, can be left in a control room where the conditions are much less difficult. Secondly, the capability of the central unit to process the optical information coming from two probe heads significantly reduces the overall costs by measurement points. The detection sensitivity limit achieved is 0.1 mg/m³ with normal stack diameter. The accuracy is around 5% depending on the care devoted to the calibration process. The response time can be adjusted over a large range but is typically set at 10 seconds.

Concentrations of volatile organics in a soil pore-gas plume were measured using a commercially available multigas monitor. The monitor is a photoacoustic radiometer (PAR) controlled by an on-board, programmable microprocessor. The measurements determine the extent and location of the vapor plume in the subsurface. At least twelve wells surrounding the sources are measured quarterly. The sources are located in former liquid chemical waste disposal pits and shafts at Los Alamos National Laboratory. The primary constituents of the plume are 1,1,1 trichloroethane (TCA), trichloroethene (TCE), and tetrachloroethene or perchloroethene (PCE). Four quarters of data are presented for TCA. All were used primarily as solvents and degreasers. Previously the composition of the vapor plume was determined by gas chromatography mass spectrometer (GCMS) methods. Photoacoustic radiometry and gas chromatography are discussed giving the advantages and disadvantages of each method, although in this program they are basically complementary. Gas chromatography is a more qualitative method to determine which analytes are present and the approximate concentration. Photoacoustic radiometry, to function well, requires foreknowledge of constituents and serves best to determine how much is present. Measurements are quicker and more direct with photoacoustic methods. Once the constituents to be measured are known, the cost to monitor is much less using photoacoustics, and the results are available more quickly. The photoacoustic radiometer uses narrow band filters in the region where trimmer or higher molecules have vibrational and rotational resonances, from 2.5 to 15 micrometers (4,000 to 650 reciprocal centimeters). The multigas monitor used is a Model 1302 manufactured by Bruel and Kjaer, a Danish company.

Aromatic molecules are detected in ambient air by a method that provides on-line results. The method is based on sensitive multiphoton ionization (MPI) of these molecules by UV laser pulses. Ions are identified and quantified by their induced electrostatic mirror image during their flight toward a collecting electrode. Only moderate vacuum is needed and quantification is straightforward. The expected performance of the new detection principle is analyzed by computer simulations, and then tested for some aromatic compounds in ambient air (ppm to ppb range). The method has the potential of simultaneous multicompounds analysis, however, it has only been tested for simple mixtures. The very simple experimental setup that is used is compensated by a comprehensive set of chemometric algorithms. These algorithms are needed for identification of aromatic ions and for resolution of mixtures. 124

A passive optical chemical sensor is described that responds to interrogation by a pulsed near- IR optical transceiver over a line-of-sight path. The chemical detection method is based on changes in the near-IR optical transmittance of a dye film on a glass substrate that forms an integral part of the sensor. The response of the sensor to a chemical is encoded onto the signal returned to the transceiver using a re-entrant optical-fiber delay line. For each interrogating optical pulse, this sensor produces a characteristic sequence of return pulses from which the presence of a chemical can be determined. The uniquely identifiable response of the sensor can also be used to identify individual sensors. The sensor is capable of quantitative measurements, it is relatively insensitive to atmospheric conditions over the transmission path, and it has a high signal-to-noise ratio. The operation of the sensor with a semiconductor-based laser transceiver is demonstrated using reagents which exhibit near-IR optical changes in the presence of specific pollutants. This technique is readily adaptable for the sensing of a wide range of hazardous chemicals in both inaccessible and dangerous environments. Modified sensors can also be adopted for use in area protection applications.

The identification of gases and the measurement of their concentration in a mixture is important in a variety of applications such as gas leak detection, process monitoring and control, and pollution control. Many gases can be uniquely identified by their optical absorption spectra. In a mix of gases, the individual species can be identified by measurements at several wavelengths and the knowledge of the absorption strengths. The advantages of these optical absorption techniques can often be utilized to the fullest only if the technology used is capable of measurements over a wide wavelength range. Instruments based on pyroelectric array detectors can utilize both dispersive and nondispersive techniques, and operate over the entire infrared region since the detectors themselves are not intrinsically wavelength sensitive. In this paper, the construction and use of infrared pyroelectric arrays suitable for gas detection and monitoring are described.

Measurements made using two different types of ammonia monitors during a two-month field study in the summer of 1994 are discussed. The first instrument was a diode-laser based open path monitor designed for automated operation in an industrial environment. The second is a point monitor based on thermal decomposition of ammonia to NO and subsequent analysis by O₃ - NO chemiluminescence. The two monitors provided consistent measurements of ammonia during weeks of continuous unattended operation.

Three versions of a near infrared system based on commercial communication type laser diodes have been developed. They have high selectivity and good sensitivity for a number of important gases. All three systems use a common control and data logging and analysis box. The LASAIR-R is a simple, inexpensive, remote sensing instrument using a single 10 cm Cassegrain telescope to both transmit and receive the laser beam. The LASAIR-S is a system for continuous, non-extractive stack monitoring. Fiber optics are used to take the laser beam from the control box (suitably located in the plant), to the stack and to bring the return back to the box. The LASAIR-P is a point source instrument using a multipath cell inside the box to provide the sensitivity required. The ease of operation and the relatively low cost should make these systems an attractive method for measuring specific gases for industrial and regulatory markets.

The use of a modulated, high-intensity green LED light source has made it possible to design a highly accurate opacity monitor with no continuously moving parts. Any possible gain drift between reference and measurement detector electronics is eliminated by alternating the measurement LED with a second LED which floods both detectors with light. The signal ratio with the flood LED depends only on the relative responsivity of the two channels, and so it is possible to correct for any gain drift. Laboratory and field testing have shown that the instrument can measure opacity with an accuracy of better than 1% and is capable of meeting compliance requirements in both the USA and Europe.

Traditionally, mid infrared detection has been performed using black body sources and filters. With the availability of infrared LEDs, which emit between the 2 - 5 micrometers wavelength, solid state gas cells can be designed which eliminate the broad spectrum problem of black body source and allow ac signal detection without mechanical chopper wheels. Dedicated microprocessors also allow other advantages, including over-sampling and, in certain applications, emitter low power mode to reduce power consumption. Results are shown for gas cells to detect carbon dioxide and hydrocarbons. LED optical gas cells are applicable to systems that require low power drain, small size, log-term stability and/or fast warm up time. Laser Monitoring Systems Ltd has developed a family of infrared LEDs with narrower optical bandwidth that can be optically modulated by electrical pulses. These infrared LEDs can thus replace the thermal source, bandpass filters and chopper wheel of the conventional monitor, giving a solid state, lower powered, fast response and contact instrument.

In recent years there has been renewed interest in using diode laser based sensors for environmental monitoring, industrial process control, and medical diagnostics applications. Diode lasers have the advantages of small size, non-intrusiveness, speed, ease of use, and high detection sensitivity. Several spectroscopic detection techniques can be employed with diode lasers, and digital signal processing algorithms can be used to enhance the detection sensitivity of a system. In our laboratory we used the following digital signal processing techniques to enhance the sensitivity and accuracy of near- and mid-infrared diode laser sensors: digital bandpass, Wiener, Kalman, and matched filtering, and a general least-squares fit. These digital signal processing algorithms have enhanced the signal-to-noise ratio of our sensors by an order of magnitude.

We describe room-temperature 2.78-micrometers AlGaAsSb/InGaAsSb multi-quantum well lasers. Pulsed laser operation was observed with threshold currents of 1.1 A, a maximum power output of 95 mW, and a maximum differential quantum efficiency of 9%. Lasers operated pulsed up to 60 degree(s)C with a characteristic temperature of 58 K over the range of 0 - 40 degree(s)C. Continuous wave operation was observed up to 200 K, with a peak emission wavelength of 2.665 micrometers . To date, 2.78 micrometers is the longest emission wavelength for a room-temperature III-V laser.

Detection of chemical vapors with a remote sensor is a requirement for both military defense and civilian pollution control. The FLIR is a natural instrument from which to build a chemical sensor since most chemical vapors of interest are spectrally active within its operating wavelength range, it is widely distributed in the battlefield, and it is becoming a standard surveillance tool in police departments. Additionally, the output image provides a 2D concentration map of the cloud which is easily interpreted by a lightly trained operator. A system has been designed to provide the spectral sensitivity in a dedicated instrument or to place a chemical detection capability as an adjunct function in a military thermal imager. In the latter case an additional detector array which is spectrally filtered at the focal plane is added to the imager. Real-time autonomous detection and alarm is a military requirement and is desired for commercial use. A detection system model based on a Gaussian vapor concentration distribution has been the basis for detection algorithms. Image processing and analysis methods have been based upon information theory. These techniques extract the cloud image from a clutter scene and perform a limited vapor classification. These methods are suited to hyperspectral imagery.

FTIR-emission spectroscopy detects the thermal radiation of hot exhaust gases, yielding all information about its compounds during one measurement. Apart from the interpretation of smoke stack measurements, FTIR-emission spectroscopy as a remote sensing technique was further developed for analyzing layered plumes, especially aircraft engine exhausts in a program of the German Science Foundation (DFG) on the effect of air traffic on the environment. The measurements shall be used as input data for model calculations and to validate the extrapolated emission data at flight altitude. The evaluation of the spectra with respect to the gas composition contains a line-by-line calculation of the transmittances of several layers of the exhaust plume (temperature- and concentration-gradients) followed by the radiative transfer through the medium towards the detector. The spectral input data are taken from the HITRAN 92 database. After the spectroscopic determination of the plume temperature and its profile from the CO₂-band around 2400 cm^-1, one obtains the total mass of the single gas species in the field of view of the spectrometer. Comparing the measured data for CO₂ with the theoretical emission index from ideal stoichiometric combustion, one obtains the emission indices for the other measured species. Knowing the fuel consumption of the engine, one gets the emission rates of the compounds in g/s. Apart from future applications for the turbine development and the engine-status control after a certain flight time, this remote sensing system can deliver emission data of aircraft engines and the temperature decay of the exhaust plumes at all altitudes.

The Gas Research Institute (GRI) has been investigating improved methods for the detection of gas leaks, particularly from buried pipes. Detection of natural gas leaks by infrared remote sensing, using topographical targets, can provide a significantly improved method for gas leak surveys, where the remote sensing system is capable of scanning large areas for leaks. For any candidate remote sensing system, the performance goal of greatest interest is the detection limit (DL), which should be as low as possible. A method is described by means of which a realistic DL may be estimated before the start of any proposed R & D project. A key feature of this method is the ability to challenge candidate remote sensing systems with a realistic 3-D model of small turbulent plumes from ground level gas leaks. To obtain these 3-D models, a novel electro-optical technique was developed in which real-time infrared optical density distributions and fluctuations of gas leak plumes from controlled releases of methane were captured as video images. These optical density plume images may be used with the infrared beam geometry of the candidate remote sensing system to achieve realistic estimates of the DL.

Usual sampling methods and instruments for checking compliance with `threshold limit values' (TLV) of gaseous components do not provide much information on the mechanism which caused the measured workday average concentration. In the case of noncompliance this information is indispensable for the design of cost effective measures. The infrared gas cloud (IGC) scanner visualizes the spatial distribution of specific gases at a workplace in a quantitative image with a calibrated grayvalue scale. This helps to find the cause of an over- exposure, and so it permits effective abatement of high exposures in the working environment. This paper deals with the technical design of the IGC scanner. Its use is illustrated by some real-world problems. The measuring principle and the technical operation of the IGC-scanner are described. Special attention is given to the pros and cons of retro-reflector screens, the noise reduction methods and image presentation and interpretation. The latter is illustrated by the images produced by the measurements. Essentially the IGC scanner can be used for selective open-path measurement of all gases with a concentration in the ppm range and sufficiently strong distinct absorption lines in the infrared region between 2.5 micrometers and 14.0 micrometers . Further it could be useful for testing the efficiency of ventilation systems and the remote detection of gas leaks. We conclude that a new powerful technique has been added to the industrial hygiene facilities for controlling and improving the work environment.

Recent food poisoning incidents have highlighted the need for inexpensive instrumentation that can detect food pathogens. Instrumentation that detects the relatively strong ultraviolet (UV) fluorescence signal from the aromatic protein amino acids in bacteria could provide a solution to the problem of real-time pathogen measurements. The capabilities of UV fluorescence measurements have, however, been largely ignored because of the difficulty in identifying pathogens in the presence of interfering backgrounds. Implementation of fluorescence measurements thus requires methodologies that can distinguish fluorescence features associated with pathogens from those associated with proteins, harmless bacteria, skin, blood, hair follicles, pesticide residue, etc. We describe multispectral UV fluorescence measurements that demonstrate the feasibility of detecting and identifying protein, DNA, and bacteria using a relatively simple UV imaging fluorometer and a unique multivariate analysis algorithm.

For the monitoring of hydrocarbons and toxic air contaminants, Fourier transform infrared (FT-IR) spectroscopy has advantages in the ability to rapidly measure multiple species accurately at low concentrations. During the last few years, FT-IR spectrometers have improved substantially in ruggedness, speed, sensitivity, and flexibility for performing air emission measurements. This paper discusses advances made at On-Line Technologies, Inc. (On-Line) in: a rugged interferometer, an advanced data system, linearized photoconductive detectors, analysis software, and operating software. These improvements in the FT-IR hardware allow improvements in detection sensitivity, scan speed, and the ability to operate in harsh environments.

The lightweight standoff chemical agent detector (LSCAD) is an infrared Michelson interferometer operating in the 8 - 12 micron band and is designed primarily for military applications. The first group of prototypes has been delivered and is undergoing testing. A secondary and no less important mission of LSCAD is its application to the civilian environmental monitoring field. Trials with earlier systems at industrial sites have been successful. The system is designed to be operated from a vehicle while on the move. Platforms which have been used are road vehicles, helicopters, unmanned air vehicles (UAV), and scanning from a fixed emplacement. To meet the restrictions of military applications, the prototype system has a weight of about 22 lbs and is approximately 0.3 cu ft in size. It employs an onboard instrument control, data collection, and analysis and detection decision system which is key to its real-time operation. The hardware, data system, and preliminary results are discussed.

Recent environmental regulations, including the Clean Air Act and the Enhanced Monitoring Regulations, may require continuous emissions monitoring (CEM) of hazardous air pollutants (HAPs). A promising technique for this application is Fourier transform infrared spectroscopy (FTIR). FTIR spectroscopy can, in principle, be used to monitor virtually any gas phase species. Two evaluations of FTIR CEM systems are discussed. The first study, performed in 1993 - 94, compared two FTIR CEM systems on a side-by-side basis in an extended field test at two coal-fired electric power plants. The FTIR CEM systems monitored the legally mandated criteria pollutants and diluents (CO, CO₂, NO, NO₂, and SO₂) as well as H₂O. In addition, one system monitored two HAPs (HCl and HF) and NH₃. The FTIR CEM measurements were compared with those from the compliance CEM systems at the facilities. Several relative accuracy test audits were also performed to verify the FTIR CEM accuracy. The second evaluation was recently commenced on behalf of the Environmental Protection Agency. In this study, FTIR CEM systems are evaluated specifically for the monitoring of HAP species by conducting laboratory and field tests. The evaluation culminates in the development of proposed performance specifications and protocols for FTIR CEM systems.

Interferant spectral features that are stable in both time and optical frequency oftentimes can be made negligible with respect to spectral features of interest by simple data processing techniques such as absorbance subtraction. With varying degrees of success more sophisticated processing of these same spectra can reject these interferant spectral features even when not stable in time. Beyond this, a classic approach to rejecting spectral interferants is to operate at higher and higher spectral resolutions so that ultimately the interferant feature separates from the feature of interest so that it is of negligible effect as an interferant. For a given observation time this approach results in a loss of radiometric sensitivity. A further reduction in radiometric sensitivity may occur since the maximum allowed etendue in a fixed parameter system must also be decreased to accommodate the higher resolution. (This reduction in etendue is more likely in the instance of a process control application as opposed to an open path monitoring application). The use of offset scanning and field widening as techniques for regaining this lost sensitivity are discussed.

Beam-steering mirrors and long-range infrared sources can be used to enhance the coverage offered by bistatic long-path FTIR monitoring systems. Factors involved in mirror design for industrial applications are discussed, and data from a typical plant installation are presented. Moderately severe vibration was shown to have no discernable effect on results. Long-range infrared sources which allow one FTIR and two remote sources to monitor a one-kilometer fenceline are discussed, and data from an industrial installation are used to contrast FTIR operation at 120 - and 450-meter pathlengths.

This paper presents a performance investigation of a number of available gas analyzers for ammonia monitoring in flue gases. The measurement systems included in the study were: MCS 100 (Perkin-Elmer), GASMET (Temet Instruments), OPSIS (OPSIS AB), GM 30 (Sick Opto-Electronic) and DOAS (Vattenfall Utveckling AB). The investigation focused on parameters such as the effects of interfering gases, comparisons between measured absolute concentrations of ammonia and obtained response times. The test program followed two stages: (1) measurements at a pilot scale oil burner for which the gas composition could be varied by injecting test gases, and (2) a comparison between the systems at a waste incinerator plant during various operating conditions. Results and experiences from the field testing and the measurements at the oil burner are presented.

A program was undertaken to evaluate FTIR for use in monitoring acid and solvent stacks in the semiconductor industry. The program consisted of an initial laboratory feasibility effort followed by field testing and ultimately a system development program. The clear result of the feasibility and field tests was that FTIR is an appropriate technology for use with these sources. In this paper we present the details of the laboratory and field tests and briefly outline the system that was developed as a result of the program. 12

Development of chemical detection algorithms for open-path FTIR is complicated due to the restricted release of the target compounds. The testing and verification of these algorithms are often impossible since the toxic target compounds can never be released outside the laboratory. A method of generating synthetic FTIR data by introduction of laboratory absorbance spectra into previously collected clean reference backgrounds facilitates this algorithm testing. A method of synthesizing `field grade' spectra has several additional advantages over actual open air releases. The cost of synthetic data is insignificant compared to the cost of data collected at actual open air releases. Unlike open air releases, the synthetic data's concentration pathlength (CL) and cloud temperature (Tc) are precisely known and easily modified. This capability makes it possible to evaluate the precise limit of detection for each of the algorithms being considered. This method works equally well for passive FTIR (using natural radiation as the source) or active FTIR (using a hot source). It is shown that synthetic spectra and real spectra of a target cloud at the same concentration pathlength and cloud temperature are in good agreement.

Recent conferences have discussed both active and passive FTIR remote sensing. However, the importance of the agent cloud temperature has not been discussed. A passive radiation model was developed that includes the effect of the agent cloud temperature. This model was compared with Beer's law as a function of temperature difference and concentration pathlength. The error in the absorbance calculated with Beer's law increases with decreasing temperature difference and with increasing concentration pathlength. The applications of the model include passive algorithm development and synthetic data production.

Environmental monitoring with passive Fourier transform infrared (FTIR) spectroscopy offers an effective method for the identification and quantification of hazardous gas pollutants. Infrared spectroscopy reveals the spectral signature of the pollutant when there is a temperature difference between the pollutant and the background radiation, resulting in emission or absorption by the pollutant. The US Army has a lightweight standoff chemical agent sensor system that generates 1024-point interferograms. The interferogram, being nonstationary, has special features that develop as a function of time. Appropriate signal processing techniques enable real-time detection and can eliminate the need for background radiation references. An algorithm has been developed for the detection of gaseous pollutants/chemical agents with single- or multiple-peak spectra. It exploits the time-dependent spectral behavior and employs signal processing techniques to enhance the spectral signature of interest in both time and frequency domains jointly, thus facilitating detection. The algorithm has been successfully developed and tested, via laboratory and real data, for the single-peak spectral signature pollutant SF₆; the signal processing concept has been extended to DEMP, DIMP, DMMP, and TEP as representatives of multiple-peak spectral signature pollutants. The algorithm software is written in the C language; the SF₆ algorithm was implemented on the Motorola M96002 DSP chip for real-time processing studies.

Remote monitoring of molecular species in the atmosphere is accomplished using a Fourier transform infrared (FTIR) spectrometer. Advanced processing algorithms utilized by AIL Systems include the classical least squares (CLS) technique as well as a more recently developed approach which combines digital finite impulse response filtering, adaptive sampling, and artificial neural networks (ANN) to improve detection sensitivity and estimation accuracy. This paper presents a comparison between the CLS and the ANN methods in estimating concentrations of multicomponent mixtures. Detection improvement of ANN over CLS has been demonstrated by examining SF₆ in a stack plume and toluene in a laboratory experiment.

Passive FTIR remote sensing measurements were made to test real-time detection of an SF₆ seeded stack plume using a probabilistic neural network (PNN) algorithm. The plume concentrations were determined using a classical least squares (CLS) algorithm and compared well with calculations using measured flow rates for the SF₆ and the waste stream.

The signals obtained from a differential absorption lidar (DIAL) when the beam is directed through an external gas cell have been simulated in order to evaluate the use of such cells for checking DIAL performance and calibration. A particular concern has been to examine how the backscatter coefficient of the gas in the cell would affect the measurements. The results of the simulations show that with high spatial resolution, concentration measurements are not highly sensitive to the amount or nature of the scatterer in the cell. When the spatial resolution of the DIAL is comparable to the cell dimensions or greater, the sensitivity of concentration measurements to variations in aerosol content is much greater and significant errors can occur unless there is a relatively close match between the cell and background backscatter coefficients.

The performance of a mobile CO₂-laser-based LIDAR is demonstrated.

Many of the 189 hazardous air pollutants (HAPs) listed in the Environmental Protection Agency regulations can be monitored by frequency agile CO₂ DIAL (FACD) systems. These systems can be used to survey industrial and military installations and toxic waste repositories at ranges of a few kilometers from emission sources. FACD systems may become a valuable tool for detection and estimation of a wide array of HAPs. However, in most cases, several of the listed HAPs will be present simultaneously and discrimination of one HAP from another based on differences in spectral characteristics can be challenging for FACD systems. While FACD hardware is mature and is capable of addressing these discrimination issues, multiple-contaminate separation algorithms need to be developed. A one week field test was conducted at Los Banos, California, to gather multiple HAP data that will be used for future algorithm development. A vapor chamber was used to control disseminated concentrations of each HAP and reduce effects of atmospheric turbulence and wind direction and speed. Data was collected for several chemicals injected into the vapor chamber simultaneously. The data and results from the field test are presented and calibration issues are discussed.

LIDARs are powerful devices for remote detection of atmospheric pollution. However calibration of data is difficult as there are no other methods that allow for fast non interfering remote measurement of the integrated concentration. In a unique field test two similar coherent LIDARs were used to detect gaseous emission. Fast response time (1 sec) and good quantitative correlation of the measurements demonstrate the applicability of the technique.

The design and several applications of an airborne lidar system are described. The system allows instantaneous, non-invasive optical measurements of pollutant concentrations in the atmosphere. In the measurement of atmospheric mercury, the detection limit of the system is better than 1.0 part per trillion by volume (mercury). The system is useful for investigating mesoscale, small synoptic, large synoptic and planetary scale pollution phenomenon, for locating previously unknown emission sources, and for obtaining detailed information about specific plumes. For wet and dry deposition rates studies, the system offers a cost effective alternative to ground-based monitoring stations for Rossby (Ro) numbers on the order of 1 to 100.

Both hardware and software methods are used to extend LIDAR detection capability in terms of range resolution and concentration threshold. Non overlapping targets are used at different ranges along the LIDAR line of sight (LOS) to replace the dependence on low aerosol backscattering. Methods of signal processing are used in concentration calculations. Presented experimental data demonstrate the method capability.

Tethered and free-flying manned hot air balloons have been demonstrated as platforms for various atmospheric measurements and remote sensing tasks. We have been performing experiments in these areas since the winter of 1993. These platforms are extremely inexpensive to operate, do not cause disturbances such as prop wash and high airspeeds, and have substantial payload lifting and altitude capabilities. The equipment operated and tested on the balloons included FTIR spectrometers, multi-spectral imaging spectrometer, PM10 Beta attenuation monitor, mid- and far-infrared cameras, a radiometer, video recording equipment, ozone meter, condensation nuclei counter, aerodynamic particle sizer with associated computer equipment, a tethersonde and a 2.9 kW portable generator providing power to the equipment. Carbon monoxide and ozone concentration data and particle concentrations and size distributions were collected as functions of altitude in a wintertime inversion layer at Logan, Utah and summertime conditions in Salt Lake City, Utah and surrounding areas. Various FTIR spectrometers have been flown to characterize chemical plumes emitted from a simulated industrial stack. We also flew the balloon into diesel and fog oil smokes generated by U.S. Army and U.S. Air Force turbine generators to obtain particle size distributions.

New algorithms are developed to improve the methodology of the ozone profile extraction from the signals measured by an ultraviolet DIAL system in a turbid troposphere. A routine procedure is developed to estimate the likely boundaries of the uncertainty in the retrieved ozone concentration profile caused both by the errors in the measured signals and by an uncertainty in the atmospheric characteristics used for the ozone concentration correction (specifically, by uncertainties in the assumed aerosol backscatter-to-extinction ratio and spectral dependence of the aerosol extinction and backscattering). The algorithms are integrated into a computer program, and a preliminary verification of the new technique for the ozone concentration derivation is made with one and two pairs of the signals, measured at the on and off wavelengths of the DIAL system.

We have designed a very compact, low cost lidar system designed for profiling of aerosols in the planetary boundary layer. Our design emphasizes portability, reliability, ease-of-use, and the lowest possible cost. Our goal is an instrument which can provide easy and reliable characterization of the boundary layer for users in operational meteorology or air quality management. The lidar transmitter is a diode laser array. As compared with more conventional laser transmitters, the diode array offers overwhelming advantages in compactness, reliability, and cost. The emission wavelength of the AlGaAs diode array is well matched to the peak sensitivity of silicon avalanche photodiodes. The transmitter and receiver are polarization multiplexed through a common aperture. A relatively large (37 cm) optical aperture compensates for the low transmitter peak power. Since the main mission of this particular lidar is measurement in and around major urban areas where aerosol loadings are generally high, the modest sensitivity is not a severe limitation. The transmitter beam is eye- safe at all ranges. Control and data acquisition are managed by a portable computer. To demonstrate the capabilities of the design, we show simulated results under a wide variety of atmospheric conditions.

We have developed a new eye-safe, high power lidar system which uses a Nd:YAG pumped KTP optical parametric oscillator (OPO) as the laser source. The output power of the OPO was about 170 mJ/pulse with a wavelength of 1.57 microns. Preliminary atmospheric lidar returns have been measured with this system out to ranges of 5 km.

Doppler lidars can be separated into two main categories by the detection technique used, coherent or incoherent. This paper focuses on the differences between the two types of Doppler lidar and the effect of speckle on each. Coherent Doppler lidars make use of a local oscillator heterodyning system similar in principle to a Doppler radar to determine Doppler shift while incoherent lidars typically use an interferometric technique to resolve the small spectral shift. The effect of laser speckle on lidar measurements in general has become a topic of great interest in recent years because in many cases it limits the ultimate resolution or accuracy of the measurement. In the case of Doppler lidars, speckle has very different effects on coherent and incoherent Doppler detection systems. Due to the single-shot nature of coherent lidar measurements and the narrow field of view required, many shots of data are lost due to speckle. The larger fields of view used for incoherent Doppler lidar as well as the inherent multiple pulse averaging make speckle significantly less of a problem for these systems.

A state-of-the-art, dual-use, mobile sensor suite has been developed incorporating both active, multi-wavelength, laser remote sensing technologies, as well as passive multispectral imaging systems. This paper discusses the current status and objectives of work ongoing at Battelle in the field of remote sensing for chemical/biological warfare (CBW) agents and environmental applications.

The hemispherical optimized net radiometer (HONER) is an instrument under development at the Los Alamos National Laboratory as part of the Atmospheric Radiation measurements/Unmanned Aerospace Vehicles (ARM/UAV) program. HONER is a radiometer which will either measure directly the difference between the total upwelling and downwelling fluxes or the individual fluxes and will provide a means of measuring the atmospheric radiative flux divergence. Unlike existing instruments which only measure the upwelling and downwelling fluxes separately, HONER will achieve an optical difference by chopping the two fluxes alternately onto a common pyroelectric detector. HONER will provide data resolved into the two relevant spectral bands; one covering the solar dominated region from less than 0.4 micrometer to approximately 4 micrometers and the other covering the region from approximately 4 micrometers to greater than 50 micrometers, dominated by thermal radiation. The means of separating the spectral regions guarantees seamless summation to calculate the total flux. The fields-of-view are near-hemispherical, upward and downward. The instrument can be converted, in flight, from the differential mode to absolute mode, measuring the upwelling and downwelling fluxes separately and simultaneously. The instrument also features continuous calibration from on-board sources. We describe the basic design and operation of the sensor head and the on-board reference sources as well as the means of the initial deployment on a UAV. This instrument can also be used in ground-based, space, or other airborne applications.

DIAL lidar for water-vapor and temperature remote sensing in the eye-safe two micron region has been receiving much interest. Such systems rely on accurate spectral line characterization. Typically spectral line properties are taken from the HITRAN database. A series of transmittance measurements are made to complete and improve the HITRAN database in this important spectral region. A 3-meter base-path White cell attached to a BOMEM DA3.02 is used for the transmittance measurements. The White cell is set to a path length of 216 meters for all experiments. Measurements of pure water-vapor, nitrogen broadened water-vapor, pure carbon dioxide, and nitrogen broadened carbon dioxide are collected at room temperature. Data analysis is performed on water-vapor lines that are relatively temperature insensitive and carbon dioxide lines that are relatively temperature sensitive over the range of typical atmospheric temperatures. The measured spectrum is converted to the absorption coefficient and is nonlinear least squares fitted to determine the spectral line parameters. Some lines show good agreement (within a few percent) with the HITRAN database, other lines disagree by more than +/- 10%. Thus care must be exercised in applying the HITRAN database to DIAL lidar applications. New parameters are obtained that are not available on the current 1992 HITRAN database, such as the self width and pressure shift.

We describe a multispectral ultraviolet (UV) fluorescence laser remote sensing system developed to detect and identify airborne pollutants. The system uses a UV laser source that is continuously tunable from 250 to 400 nm in conjunction with a database of fluorescence signatures and multivariate analysis algorithms to obtain species concentrations from multispectral UV fluorescence measurements. As presently configured, the system is designed to operate with sequentially transmitted laser wavelengths between 250 and 400 nm at a pulse repetition rate of 10 Hz and is designed to map chemical concentrations with a range resolution of approximately 1 m. We describe the optical detection, associated data acquisition and control electronics, and tunable UV laser transmitter. We also describe a unique software package used for instrument setup and control. Based on sensitivity calculations, 1 ppm-m of toluene can be detected at a range of approximately 2.0 km with a range resolution of 1 m and a signal-to-noise ratio of approximately 3.

Detection of different chemical species in the atmosphere is performed with a frequency- tunable middle IR laser. The design of lidar for this range is discussed. Two pulses can be used, one propagates to an object another provides receiving a reflected signal. When emitting, it is possible to start with YAG:Nd repetitively-pulsed solid-state laser radiation of 1.06 micrometers , 1 - 8 J, 10 - 100 Hz. The first pulse is further converted by OPO in 1.5 - 2.1 micrometers range and then into 4 - 14 micrometers radiation with SRS in hydrogen or other gases. To receive a weak reflected signal of 4 - 14 micrometers we propose using a hydrogen or other Raman amplifier which is pumped with the second OPO pulse (two pulses spaced by 2L/c, L being the distance from an object). A sensitivity for the method better than 10 photon per mode is achieved. For a wavelength less 4 micrometers it is possible to use only one OPO (for example by LiNbO₃) as an emitter and receiver.

This brief review deals with various types of new multipass systems developed for urgent high resolution spectroscopic applications at the Institute of Chemical Physics of the Russian Academy of Sciences. Some of them have been widely acknowledge and independently applied in different fields of modern science and technology, i.e., laser technology, metrology, spectral instrument engineering and environment.

A field-of-view stack plume model, developed for use with remote optical sensors, was evaluated using field data collected during February and March 1994 at a Department of Energy test site where homogeneously mixed and heated sulfur hexafluoride in air were intermittently released under controlled stack conditions from a 16-inch-diameter 70-foot stack. The duration of each of the intermittent periods ranged from approximately 2 to 4 hours. A total of 27 hours of released occurred over a 3-week period. The model is 3D with animation, focuses on the first 100 meters downwind from the stack, and has a temporal resolution of 1 second. It determines concentration pathlength for up to 6 compounds as well as a bitmap of plume temperatures and concentration. The model's performance was evaluated by comparing field observed versus model-predicted plume vertical thickness, which were monitored in near real time using infrared cameras operated in the sulfur hexafluoride band and mounted alongside the plume. For a sensor-plume scenario, comparisons were also made between model-predicted concentration pathlengths and concentration pathlengths derived from the observed vertical plume thickness, measured wind speed, gravitational effects, and conservation of mass in the plume. In predicting the plume's vertical thickness through its center, the model's range of accuracy was +34.0 to -21.4% for the inclusive distances between 5-50m from the stack. In predicting the plume's concentration pathlength for sulfur hexafluoride, this translated to a range of accuracy of +27.1 to -25.4% for a specific plume-optical sensor scenario. The arithmetic mean for this range was +5.19%.