The Stratospheric Wind Interferometer for Transport Studies (SWIFT) is a satellite-born limb-viewing instrument which will be capable of globally measuring horizontal winds at altitudes of between 20 and 40 km with a precision of < 5 m/s, a vertical resolution of 2 km and a horizontal resolution on the order of a hundred km. SWIFT will map stratospheric dynamics. The data from the instrument will be important input for models which seek to predict the global distribution of stratospheric ozone. In addition, the SWIFT data will provide observational input to tropospheric weather models, which are currently being extended to the stratosphere. With global stratospheric wind data, these enhanced models have the potential to significantly improve weather forecasting in the troposphere. The instrument will observe a thermal emission line of an abundant atmospheric constituent near 8 micrometers using a field widened Michelson interferometer. A doppler shift of the emission line is detected as a phase shift at the output of the interferometer. A 2D array detector monitors the phase both perpendicular to and along the limb, thus mapping the velocity field. The fundamental feasibility of the instrument will be shown. The basic instrument requirements are described and the instrument parameters are derived from them. The instrument will utilize radiatively cooled optics and Stirling cycle coolers for the detector and filters. This instrument will be suitable for inclusion on a medium to large satellite with multiple instruments. The lack of cryogens is consistent with its intended use on the operational weather satellites of the future.

A method is described for obtaining four simultaneous phase- stepped images from a Michelson interferometer in order to measure the Doppler shift of a spectral line. One of the Michelson mirrors is divided into quadrants and each quadrant coated separately, so the path difference varies by about (lambda) /4 from one quadrant to another. An image of the mirrors is formed outside the interferometer, where the light from the quadrants is diverted in different directions, and four separate images of the field of view are formed, one for each quadrant. For a given direction in the field of view, the fringe is sampled at four points on the interferogram separated by (lambda) /4 and from these four intensities, the phase of the fringe is calculated. Doppler shifts of the spectral line are seen as changes in the phase of the fringe. In earlier versions of the imaging Doppler Michelson technique, the sampling was done in sequence. Simultaneous sampling eliminates the errors caused by intensity variations during the measurement, making the technique useful for rapidly varying sources such as aurora.

Active atmospheric sounding with lidar in principle offers great advantages over passive sounding, including higher spatial resolution and better species selectivity. These improved capabilities have been unavailable in practice due to the great spacecraft burdens of conventional lasers. The long range and high ground speed of spaceflight operation lead to high laser output power requirements. The low efficiency of most lasers leads in turn to exorbitant electrical power and heat removal requirements. Space qualification of Nd:YAG will provide a high efficiency laser suitable for elastic backscatter measurements, but his laser will not be capable of DIAL operation, nor is it practical for an eye-safe wind speed Doppler lidar. Alexandrite is a laser source that is being proven in certain demanding lidar applications, such as resonant backscatter from mesospheric metals. This laser has the great practical advantage of tunability, permitting its use for differential absorption lidar. Laser diode pumping of alexandrite has been demonstrated, using the recently developed short wavelength, high power laser diodes. Laser diode injection seeding of a ring laser yields tunability and extremely narrow linewidth, under 20 MHz. Spaceflight applications of alexandrite are considered, including two- wavelength measurements of aerosols, differential absorption measurements of atmospheric molecules, and Doppler measurement of tropospheric and stratospheric wind speeds. The lidar support requirements are compared to the capabilities of relatively small spacecraft for low cost missions.

The Network for Detection of Stratospheric Change is a set of high quality ground based observing stations, which combined with satellite observations, is intended to provide the earliest possible warning of changes in the chemistry and dynamics of the stratosphere as well as data to understand the causes of the change. There will be five primary stations, some distributed among several sties, and numerous complementary sites. Each primary station will have the same distributed among several sites, and numerous complementary sites. Each primary station will have the same complement of instruments, including UV/visible, infrared, and microwave spectrometers, lidars for temperature, aerosol, and ozone measurements, ozonesondes, and instruments for measuring UV-B irradiance. Each primary station and many complementary sites will have a high resolution FTIR spectrometer observing atmospheric absorption using the sun, and possibly the moon, as a source. Important characteristics of the FTIR spectrometers include the spectral resolution and detailed instrument line shape, the observation time, and the signal to noise ratio in the spectra. The expected performance of these instruments is described, as well as methods for testing the actual performance. In addition to determining with high precision the total column amount of various trace gases, we will attempt to derive some information on the vertical profile of some gases form the resolved line shape. For this purpose, precise knowledge of the instrument line shape is crucial. We will describe the validation of the line shape measured with the Bruker spectrometer.

Using the third version of tunable diode laser heterodyne spectrometers developed by the Tohoku University optical group, infrared absorption spectra of atmospheric O₃, N₂O, CH₄, and HNO₃ were observed at Syowa station from August 1994 to January 1995. This portable spectrometer has an ultra high spectral resolution of 0.0013 cm^-1 and a signal-to-noise ratio of 500 for 10-min scan time. From ozone absorption spectra obtained in early spring, the height profiles of ozone concentration up to 30 km were retrieved at intervals of ten minutes. These profiles showed extremely low ozone concentration in the altitude range of 15-20 km, which is a typical feature of the antarctic ozone hole. Furthermore, these profiles demonstrated the existence of rapid variations of ozone concentration in the altitude range of 20-30 km. From the potential vorticity analysis using the objective analysis data provided by the Japanese meteorological agency, it was concluded that these variations wee caused by a passage of westward traveling waves produced at the polar vortex boundary.

A Fabry-Perot annular summing spectroscopy technique has been sued at the University of Wisconsin's Pine Bluff Observatory to acquire geocoronal Balmer-(alpha) line profile data with significantly improved precision and height resolution. The double-etalon Fabry-Perot interference pattern is imaged onto a photometrics PM512 CCD chip, thus enabling light to be gathered in multiple spectral bins simultaneously. In comparison with scanning systems we used earlier, the high quantum efficiency of the CCD and the multi-channel detection associated with the Fabry-Perot annular summing technique have enabled us to save a factor of about 10 in the integration time required for studies of the line profile. As a result, we are now able to both more precisely observe the line shape of the very faint Balmer- (alpha) emission and obtain data using shorter integration times. Our data illustrate the scientific potential for using this technique for the study of very faint extended emission line sources. The increase in the signal-to-noise of our data has enabled us to examine Balmer-(alpha) profile asymmetries which we have found to be compatible with predictions that on the order of 10 percent of the geocoronal Balmer-(alpha) excitation arises from cascades due to higher-member solar Lyman series excitation. This fine structure was overlooked in previous Balmer-(alpha) studies aimed at determining non-Maxwellian dynamical properties of exospheric hydrogen; we find that cascade excitation largely masks the expected very small dynamical perturbations to the line profile at low shadow heights, and must be more thoroughly studied before drawing conclusions about exospheric dynamics. Accounting for cascade laos leads to more realistic determinations of exospheric hydrogen temperatures near the exobase.

The GLO experiment includes a ground-controlled shuttle- based UV-vis-IR spectrograph and imager set, and has flown on four space shuttle flights, including three in 1995. Each flight returned limb-view on metal atom and ion emissions in the 80-350 km tangent height region. Improved optics provided 0.3 nm FWHM resolution in the ultraviolet, and simultaneous altitude profiles were routinely measured that spanned 150 km in tangent height with 10-15 km resolution. CLouds of metal ions, particularly Mg⁺, were observed in daytime above 120 km tangent height near the geomagnetic equator. The GLO project returned approximately 30 gigabytes of spectral data in 1995. The current high altitude metal ion emission measurements are reported here.

Spectrally uniform treatment of the atmospheric radiative transfer (RI) problem has been approached through two different techniques - very high resolution line-by-line (LBL) algorithms and lower resolution band models (BM). Each has its advantages and specific applications. However, if commonality and validation of a specific pair of RI approaches is to be mutually maintained, then these codes must be continually reevaluated against both measurements and other models.

The next generation of atmospheric temperature and humidity sounders will have thousands of radiometrically accurate spectral channels throughout the infrared. The retrieval of atmospheric parameters from these radiances will stress both the accuracy and efficiency of forward model radiative transfer algorithms. We are developing a forward model for the Atmospheric Infrared Sounder (AIRS) which will fly on the EOS PM platform. The work presented here is based on algorithms developed over a number of years by McMillin, Fleming, and others for low resolution infrared sounders (HIRS) and microwave sounders. We have developed tow 'high resolution' AIRS forward model algorithms for water vapor, one based on atmospheric layers with fixed pressures and variable water amounts, and other based on layers of fixed absorber amount but with variable pressures. These algorithms are compared for speed, accuracy, ease of development, and other factors that must be considered in developing a complex operational retrieval system.

We have developed a new information-content based look-up table technique for the fast computation of near- monochromatic atmospheric transmittances in the infrared that is well suited for nadir viewing satellite and airplane observations. It allow a user to quickly compute near- monochromatic radiances using a very simple algorithm that is easily ported to many machine architectures. Radiative transfer based on look-up tables of monochromatic absorption coefficients could speed calculations, but they are impractical due to their large size and the need to interpolate long wavenumber vectors in temperature and pressure. We use a singular value decomposition to transform monochromatic look-up tables of absorption coefficients into a compressed representation that is almost 100 times smaller. Moreover, temperature and pressure interpolations can be performed in this compressed representation, resulting in significant savings in computation times and computer I/O. We start with the line-by-line computation of a set of tables of absorption coefficients for each relevant gas. Each 25 wavenumber table has 10,000 wavenumber points and 1,100 temperature/pressure layers. For water vapor we add an extra dimension to these tables that spans 5 water vapor profiles to provide variability in the self-broadening of water vapor spectral lines. On average we need 37 basis vectors for water, 12 for carbon dioxide, and 6 for each of the other required gases in order to reproduce the absorption coefficient tables to an accuracy equivalent to a nadir-viewing monochromatic brightness temperature error of 0.1K.

Space-based observation of tropospheric pollution has been identified as a high-priority atmospheric science measurement to be included in Earth science missions of the 21st century. Levels of tropospheric O₃ have been increasing and will continue to increase as concentrations of the precursor gases necessary for the photochemical formation of tropospheric O₃ continue to rise. A global tropospheric O₃ monitoring capability is critical to enhance scientific understanding as well as to potentially lessen the ill-health impacts associated with exposure to elevated concentrations in the lower atmosphere. A measurement technique to enable such a measurement capability utilizing Fabry-Perot interferometry will be presented. It involves a double-etalon series configuration FPI along with an ultra-narrow bandpass filter to achieve single-order operation with an overall spectral resolution of approximately .068 cm^-1, sampling a narrow spectral region within the strong 9.6 micrometers ozone infrared band from a nadir-viewing satellite configuration. The Fabry-Perot interferometer (FPI) provides high spectral resolution and high throughput capabilities that are essential for this measurement task. Through proper selection of channel spectral regions, the FPI optimized for tropospheric O₃ measurements can simultaneously observe a stratospheric component and thus the total O₃ column abundance. A retrieval technique employing the maximum likelihood method has been implemented and will be demonstrated for a tropical atmosphere possessing enhanced tropospheric ozone amounts. An error analysis assessing the impact on retrieved O₃ amounts form the most significant uncertainties associated with this particular measurement has been performed for several different types of atmospheres. Emphasis will be placed on a tropical atmosphere, for which sounding data have been used in the a priori information covariance matrix estimation process. An error budget has been formulated by estimating the impact on overall measurement uncertainty of the potential random and systematic component error sources. Results show the proposed instrumentation to enable a good measurement of absolute ozone amounts and an even better determination of relative changes.

Space-based observation of tropospheric pollution has been identified as an important measurement to be included in Earth science missions of the 21st century. This presentation will summarize on-going efforts focused on enabling such a new capability, a high-priority atmospheric science mission for the measurement of tropospheric ozone from a space-based platform, through the implementation of Fabry-Perot interferometry. The measurement technique involves a double-etalon series configuration FPI along with an ultra-narrow bandpass filter to achieve single-order operation with an overall spectral resolution of approximately .068 cm^-1, sampling a narrow spectral region within the strong 9.6 micrometers ozone infrared band form a nadir-viewing satellite configuration. Current research efforts are focusing on technology development and demonstration activities to address technology drivers associated with this measurement concept. To this end we have developed a small-scale, modular, double-etalon prototype FPI for laboratory characterization and testing, modelled the instrument optical configuration, and performed R and D associated with an etalon optical control scheme. This presentation will cover advancements pertaining to all aspects of this effort, however, emphasis will be placed on integration and testing activities associated with the laboratory prototype FPI. This will include multichannel operation considerations pertaining to different configurations for spectral tuning. In addition, implications associated with extrapolation toward a full- scale flight instrument design will also be addressed.

A remote measurement of the atmosphere with high spectral resolution form the ground or from space, such as might be made form one of the new generation of instruments such as the Fourier transform or grating spectrometers AIRS, MIPAS, TES, or IASI, would appear to contain a large amount of information about the atmosphere, but it is not immediately obvious how to quantify it or to use it efficiently or effectively. The usefulness of a particular remote measurement can be described by a wide range of parameters including the spatial resolution, precision and accuracy of the retrieved product. For optimization of a measurement method, however, a single scalar figure of merit is required, whereas all of the above are vectors because they are functions of altitude and/or quantity retrieved. Spatial averages of resolution, precision and accuracy could be used, but there are two quantities of general applicability which can be defined without reference to the specific retrieval method, and are therefore more straightforward in use. These are the information content, and the number of degrees of freedom for signal, the latter being a measure of the number of statistically independent quantities in any one measurement. It can be shown that both of these quantities are functions of the eigenvalues of a certain matrix, and are closely related. The information content and the degrees of freedom provide single parameters which can be used in the automated optimization of for example, instrument design parameters, the selection of microwindows or subsets of channels for retrieval, the optimization of retrieval strategy, and the understanding of the information content of a spectrum. Some such applications are illustrated by means of simulated spectra for the AIRS instrument.

A sounder using a high-finesse Fabry-Perot etalon offers substantial potential to extract temperature profiles from the stratosphere atmosphere. The multi-order etalon sounder (MOES) is such an instrument. Its extremely high spectral resolution makes it possible to selectively observe emission at the very line centers and near shoulders of individual CO₂ lines. However, the radiances at the centers of these lines can contain large non-LTE contributions originating at much higher altitudes. At high altitudes, the non-equilibrium absorption and re-radiation of solar illumination enhances the vibrational temperature compared to the kinetic temperature. The kinetic temperature profile can only be estimated from the complex line radiance spectrum by relating the observed vibrational temperature to the probable kinetic temperature. The effective separation of layer contributions requires that the instrument be designed so that (1) its dynamic range preserves the much larger range of expected radiances and (2) its spectral response function is very well known so that the line wing radiances can be accurately determined in the presence of large line center radiances. This paper discusses the retrieval of stratospheric temperatures in terms of typical measured radiance covariances, the required solar illumination model and a sensor suitable for routine temperature profile retrieval.

We have developed a retrieval algorithm for deriving the tropospheric CO profile and column amount from the radiances measured by the Measurements of Pollution in the troposphere instrument. The main components of the algorithm are a fast radiative transfer model, based on the GENLN2 line-by-line model, and a maximum likelihood inversion method. The retrieval a priori information is derived from the results of several aircraft in situ measurements and a 3D chemical- transport model. This paper discusses the CO retrieval algorithm with an emphasis on the analysis and characterization of the algorithm. Forward model and retrieval sensitivities, along with the a priori information used in the retrieval are discussed in terms of their orthogonal components. Examples of ensemble retrieval experiments are also included.

One goal of the atmospheric infrared sounder (AIRS), scheduled to fly on the EOS-PM1 satellite in 2000, is the global measurement of the atmospheric abundance of carbon monoxide (CO). ALthough it is primarily a temperature and humidity sounder for EOS, AIRS can resolve individual CO lines in a portion of the 1-0 vibration-rotation band of CO between 2170 and 2200 cm^-1, but with significant noise. Taking advantage of the almost regular spacing of these lines, we have developed an algorithm to retrieve the column density of CO from AIRS spectra using standard signal processing techniques for noise reduction. Detailed simulations indicate the capability to retrieve total column densities of CO to an accuracy of approximately 10 percent. Validation of our CO retrieval algorithm has been accomplished using a combination of in situ CO profiles acquired by an instrumented Cessna and nearly coincident infrared spectra obtained by the University of Wisconsin Madison's High-resolution Interferometer Sounder (HIS) flying onboard a NASA ER-2 during the Second Convection and Moisture Experiment in August, 1995. Excellent agreement was obtained between the retrieved CO abundance, approximately 90 ppbv, and the in situ profile above the boundary layer, approximately 80-100 ppbv. Additional HIS spectra obtained near Long Island, NY show enhanced CO levels, 1400-4300 ppb if confined to portions of the boundary layer, in the smoke plume downwind from forest fires near Westhampton, NY on August 25, 1995.

The scientific objectives and requirements for HIRDLS are presented, and the ways in which these flow down to some of the most important instrument requirements are shown. An overview of the conceptual design of the HIRDLS instrument, a 21-channel infrared limb scanner is presented, followed by a brief summary of the key requirements on the 9 subsystems, and an outline of some of their noteworthy design features.

The high resolution doppler imager (HRDI) on the upper atmosphere research satellite has been providing measurements of the wind field in the stratosphere, mesosphere and lower thermosphere since November 1991. Mesospheric temperatures, ozone and O(¹D), as well as stratospheric aerosol extinctions, are also recovered. The instrument characteristics have been carefully monitored during the nearly five years of operation. The instrument thermal and long-term drifts can be removed from the data, and wind biases are less than about 2 m/s. The interferometer sensitivity has varied by about 3 percent, most likely due to changes in the parallelism of one of the etalons. There is not indication that either the radiator or thermal blankets have shown any significant degradation. Recently, the azimuth slew rate of the telescope has displayed some variation, which may indicate an increase of bearing friction.

Sounding the stratosphere using the 4.3 micrometers CO₂ lines requires observations where radiance contributions from the very thin upper atmosphere form a significant part of the measured signal. In order to properly account for the influence of these extremely narrow emission features in the temperature retrievals, extremely high spectral resolution is required. The multi-order etalon sounder (MOES) is an instrument which capitalizes on the extremely high spectral resolution achievable with a standard Fabry-Perot etalon and on the regular spacing of the lines in portions of the vibration-rotation spectrum of gases such as CO₂. The MOES instrument simultaneously measures several identically shaped CO₂ lines when its etalon spacing is set to produce a free spectral range equal to the uniform line intervals in the spectrum. By combining the signals from a large number of lines a MOES sensor greatly improves the signal-to-noise ratio without reducing its inherent spectral resolution. A detailed design for the most recent MOES concept is presented along with its expected/simulated performance parameters.

The measurement of pollution in the troposphere (MOPITT) instrument is designed to globally map carbon monoxide and methane concentrations in the lower atmosphere from space. It will be launched on NASA's EOS-AM1 platform in mid-1998. The MOPITT engineering model has been undergoing tests at the University of Toronto Instrument Characterization Facility and the flight model will be tested in the same facility in a few months. The tests to be performed and some of the results form the engineering model are discussed.

The student nitric oxide explorer (SNOE) is a small satellite to be designed built and operated at the University of Colorado under the student explorer demonstration initiative from the University's Space Research Association (STEDI). The goal of the STEDI program is to demonstrate that low cost satellite missions can be done with large student involvement. The primary science goals of SNOE are to measure thermospheric nitric oxide (NO) and its variability over the lifetime of the mission. SNOE will also monitor the solar irradiance at soft x-ray wavelengths and the auroral energy deposition at high latitudes. Three science instruments are required to achieve the simultaneous measurements: an ultraviolet spectrometer for NO; a solar soft x-ray photometer; and a far ultraviolet photometer for studying the aurora. The instruments are designed to represent a minimum impact on the spacecraft, particularly in terms of data storage and interactions with the command and data handling system. The focus of this paper is the outline of the design of the science instruments. We discuss why these instruments are well suited for smaller, lower cost satellite missions.

Direct measurement of CCD MTF using a unique Lloyd's mirror fringe projector is described. MTF measurements on the MISR linear CCD arrays have been performed as a function of spatial frequency, wavelength, number of charge transfers, radiation dosage, and device architecture. Test results are reported here.

A unique, highly automated thermal-vacuum facility for optical testing of lenses and cameras is described. In particular, measurements of MTF, boresight, and geometric image distortion over a large parameter space including wavelength, field of view and temperature will be discussed. Unique aspects of the facility include a 'virtual nodal bench' opto-mechanical metrology system and fiber-optic illumination of mechanical reference features.

SFIM Industries has designed a new radiometer for satellite observation of the earth radiation budget at the top of the atmosphere. COmpared to previous instruments, this new radiometer halves costs, mass and probability of failure, while it improves radiometric performance significantly. The key idea to achieve these goals is to multiplex the various spectral channels of the instrument. This paper presents the main results of this study and focuses on the advantages and shortcomings of this new small size instrument.

Present trends in space vehicles are leading to smaller platforms which represent a new set of challenges and requirements. For instance, because of their smaller inertias, these vehicles are likely to be more sensitive to disturbances and experience higher levels of attitude jitter. This higher frequency motion may be unacceptable for some scientific instruments and require compensation. Hence, the bandwidth of inertial reference units may need to be enhanced if it is desired to control the high-frequency attitude jitter. In the case of line-of-sight type instruments, attitude jitter can be mitigated by incorporating a fast steering mirror into the system. To take full advantage of these devices, the spacecraft attitude needs to be measured at sufficiently high bandwidth, well beyond wheat is commonly provided by inertial reference units. Furthermore, due to cost and/or power considerations, it may be desirable to replace conventional gyros with accelerometers or quartz rate sensors, and star trackers with GPS receivers configured to measure attitude. This paper explores various ways to obtain higher bandwidth attitude measurements for the purpose of jitter control, and provides a practical solution.

Optical remote sensing plays an important role in the study of planetary atmospheres, especially in determining trace gas abundance, temperature profiles and dynamics/winds. Instruments to be flown aboard interplanetary platforms must be small, have low mass and consume little power. Fabry- Perot interferometers (FPI) satisfy these physical constraints and are capable of acquiring spectra suitable for analysis of the atmospheric parameters. Two new applications of FPI technology have recently been developed at UM/SPRL: the multiplex Fabry-Perot interferometer (MFPI) and the multi-order etalon spectrometer (MOES). The MFPI produces a broad bandwidth high resolution spectrum via Fourier transformed interferograms produced by scanning the etalon over large distances. The MOES simultaneously measures several similar lines in a regular spectrum by matching its free spectral range to the line spacing. Thus MFPI provides a means for broadening the usable bandwidth and MOES can record improved signal-to-noise spectra at extremely high resolution. This paper reports recent progress in the design, construction and testing of a prototype instrument incorporating both the MFPI and the MOES concepts using a single set of etalon plates.

An imaging spectrometer has ben designed as a new instrument for remote sensing of the atmosphere. The design has been focused on applications in the field of weather forecast, climate research and atmosphere chemistry research. The push-broom type of instrument consists of a wide field of view telescope, in combination with three spectral channels. The instrument operates without a scanning mirror. Each channel contains a grating, imaging optics and a state-of- the-art 2D CCD detector. The channel separation is performed by a dichroic filter. A sunlit diffuser is applied for the in-flight radiometric calibration and the spectral calibration of the instrument. The polarization sensitivity is minimized by the application of a polarization scrambler. The basic instrument module consists of a UV-channel, a visible channel and a NIR-channel. The main new features of the instrument are a fast and high-resolution coverage of the atmosphere, in combination with high-resolution spectral measurements. This performance is realized in a rather compact instrument. The modular instrument configuration enables an easy adaptation of the instrument for different spectral bands.

We discuss the design of tunable birefringent filters utilizing liquid crystals. The performance of several assembled filters is presented. We have incorporated nematic liquid crystals in Lyot and Solc filter designs to a low continuous spectral tunability. Liquid crystals can be manufactured as electrically variable retarders in the visible and near infrared spectral regions, and can provide filter tuning times as short as 20 msec. The performance characteristics and design enhancements of assembled tunable filters for diverse applications are discussed. These include: solar imaging in the near infrared with a narrow band filter; imaging fluorescence microscopy in the visible with a fast tuning filter; and airborne remote sensing over the 400-2500 nm spectral range with wide field of view filter.s Design considerations for improving speed, field of view, transmission and contrast of liquid crystal tunable filters are discussed.

Applications of the Army Research Laboratory Mobile Atmospheric Spectrometer Remote Sensing Rover required development of a customized computer-controlled mount to satisfy a variety of requirements within a limited budget. The payload was designed to operate atop a military electronics shelter mounted on a 4-wheel drive truck to be above most atmospheric ground turbulence. Pointing orientation in altitude is limited by constraints imposed by use of a liquid nitrogen detector Dewar in the spectrometer. Stepper motor drives and control system are compatible with existing custom software used with other instrumentation for controlled incremental raster stepping. The altitude axis passes close to the center of gravity of the complete payload to minimize load eccentricity and drive torque requirements. Dovetail fixture mounting enables quick service and fine adjustment of balance to minimize stepper/gearbox drive backlash through the limited orientation range in altitude. Initial applications to characterization of remote gas plumes have been successful.

A novel depolarizer composed of two quartz sedges is presented. The depolarization mechanism of this depolarizer lies in the double effects of integration over both frequency and space domain. The conditions of the depolarizer for effect depolarization are concluded: (1) the slope of retardance should be large enough; (2) retardance of the depolarizer should be large enough; (3) the angle between optical axes of two crystals should be 45 degrees. Furthermore, the image characteristics of the depolarizer is analyzed and image tripling is demonstrated. The experiment results show that our theoretical analysis is responsible. This depolarizer can be applied in many fields such as astronomy, remote sensor and spectroscopy.

MOPITT is a satellite instrument which will be launched in 1998 on the EOS-AM1 platform of the Earth Observing System. The primary objective of the MOPITT instrument is to enhance our knowledge of the lower atmosphere by measuring atmospheric profiles of carbon monoxide (CO) and methane. Operationally MOPITT will employ a new form of correlation radiometer known as the length modulated radiometer (LMR). To date, the LMR has been successfully implemented in a ground-based remote sounding instrument measuring CO, and is currently being implemented on two airplane-based instruments known as MATR and MOPITT-A. The operating principle of the LMR is the modulation of a static gas cell path length by means of an optically inert filler material. This paper will describe aspects of the operation of an LMR. Topics that will be covered include a discussion of the sources of optical imbalance in the LMR and the radiometric calibration of the LMR with CO. An analysis of the sources of error in the radiometric calibration of an LMR will also be presented.

To measure trace concentrations of the atmospheric radical NO₃ we are investigating the use of two amplitude stabilized diode lasers, one tunes to the center of the absorption profile, and the second tuned to a wavelength outside the absorption. This approach is taken because the absorption feature is much broader than the visible diode laser's tuning range and removing the sample concentration from the beam path to measure the baseline is difficult. This paper describes the preliminary system design, interferences expected from water, and electronics design.

Two approaches have been explored for the retrieval of atmospheric constituent and aerosol extinction profiles from radiance measurements made by a limb sounding satellite radiometer. One of the retrieval schemes can be used with different signal to noise ratios and with measurements from different spectral regions. Multiple constituents can be retrieved simultaneously. Characterization and error analysis of the retrieved products arise naturally from theoretical considerations. The algorithms have been implemented on CLAES, an infrared limb sounder on the upper atmospheric research satellite. The CLAES measurement technique requires the level 1 extracted radiance data from CLAES to be processed before they are input to the NCAR research retrieval algorithm. The algorithms are applied to blocker 3 radiance measurements and some initial results are presented.

A three-wavelength sun-photometer was designed and built. The attenuation of direct solar light, at wavelengths of 0.38 micrometers , 0.50 micrometers and 1.00 micrometers were measured. Silicon photodiodes and interference filters of 10 nm FWHM were used. Aerosols were characterized by angstrom's turbidity formula in terms of coefficients (alpha) and (Beta) and by Moon's model in terms of the precipitable water content, w, and the amount of dust particles per unit volume, d. Aerosol attenuation was calculated from the slope of Langley's plots. Several measurements were performed in the city of San Luis during summer and autumn seasons of 1996. Results corresponded to a very clean atmosphere. Weather was extremely dry during most of measurements.

The data processing of the global ozone monitoring by occultation of stars instrument separates naturally into two parts. The nonlinear spectral inversion retrieves the horizontally integrated gas densities. The vertical profiles of the gases are retrieved by using the generalized onion peeling method. The Markov chain Monte Carlo method has been used to calculate the posteriori distribution of the spectral inversion problem. This method was found to be simple and straightforward in analyzing the real posteriori distribution and confidence regions of the retrievals.

Optical measurement of the density of ozone and other atmospheric species at night is possible by using stars as light sources. The Technical Research Centre of Finland (VTT) has built a star-pointing spectrometer, which records stellar spectra by a 2D CCD-array. The spectrometer has a 'slitless' design, so it can measure the absolute intensity level of a stellar spectrum attenuated by the atmosphere. A spectral inversion method designed for the satellite-based instrument GOMOS is applied for constituent retrieval form stellar spectra measured on ground. Analysis of simulated measurements shows that when averaging over one night the total ozone column can be measured by the VTT spectrometer at an accuracy of 2-3 percent.

A ground-based instrument for measurement of perturbations of the rotational temperature and vertical column emission rate of the O₂ atmospheric nightglow layer at 94 km and the OH Meinel layer at 86 km is described with special emphasis on its suitability as a remote field instrument. Ground-based instruments are needed in the detailed study of planetary scale dynamic effects in the upper atmosphere because they show detailed perturbation development in both solar and universal time that is missed by satellite-borne instruments. Ground-based instruments must be stable, accessible to but not dependent upon operator interaction, and inexpensive. The technique of interference filter spectral imaging has shown itself to satisfy these requirements when embodied in the instrument MORTI, a mesopause oxygen rotational temperature imager. SATI represents a complete re-design of MORTI in order to make it more flexible for ground-based networks. In particular, the cryogenic cooling was replaced by thermo-electric cooling, removing the requirement for daily attention, an OH channel was added that will allow comparison of perturbation amplitudes at two significantly different altitudes, and real-time temperature and emission rate readout was incorporated into the revised software.