A new high spectral resolution (0.25 cm^-1) and high spatial resolution (2.6 km) scanning (46 km swath width) Fourier Transform Spectrometer (FTS) has been built for flight on NASA high altitude (approximately 20 km) aircraft. The instrument, called the NPOESS Aircraft Sounding Testbed- Interferometer (NAST-I), has been flown during several field campaigns to provide experimental observations needed to finalize specifications and to test proposed designs for future satellite instruments; specifically, the Cross-track Infrared Sounder (CrIS) to fly on the National Polar-orbiting Operational Environmental Satellite System (NPOESS). NAST-I provides new and exciting observations of mesoscale structure of the atmosphere, including the fine scale thermodynamic characteristics of hurricanes. The NAST-I instrument is described, its excellent spectral and radiometric performance is demonstrated, and surface and atmospheric remote sensing results obtained during airborne measurement campaigns are presented.

MIPAS-B2 is a cryogenic limb-sounder dedicated to stratospheric trace gas research. The balloon borne instrument is a precursor of the MIPAS instrument on the ESA ENVISAT satellite. In consequence, the main instrumental specifications and parameters are similar. The instrument has been flown several times successfully in the frame of European atmospheric research campaigns (SESAME and THESEO) and a satellite validation campaign (ILAS). The heart of the instrument is a Fourier spectrometer working in the mid- infrared range (4 to 14 micrometer), which is cooled before launch to its operating temperature of 210 K with solid carbon dioxide. The spectral coverage is split into four spectral channels to improve sensitivity in particular in the short wavelength region. We employ liquid helium cooled Si:As-BIB- detectors to achieve optimum detectivity. A further important part of the instrument is the line of sight (LOS) stabilization system, which is based on an inertial navigation system and can be cross-examined with the help of an additional star reference system. The instrument was flown eight times from balloon launch sites in Sweden and France. The recorded data allowed the retrieval of many trace gases. One major scientific advantage of the instrument is the simultaneous detection of whole trace gas families in the stratosphere. All relevant night-time NOy species (NO₂, N₂O₅, HNO₃, ClONO₂ and HO₂NO₂) together with the source gas N₂O were successfully analyzed.

The balloon borne IR-Fourier transform spectrometer (FTS) MIPAS-B2 has been designed for a low self-emission from each of the instrument ports leading to low noise signals and a radiometrically balanced interferometer. The radiometric accuracy depends strongly on the quality of the phase correction of interferograms and of the calibration measurements and algorithms. It could be observed that the classically derived phases of the complex spectra are in correlation with line structures in the spectrum and cause disturbed calibrated spectra. These phase functions cannot be explained by the instrumental phase due to the beamsplitter nor by sampling shifts but by the emission of the beamsplitter itself. The determination of the instrumental phase function requires to invent an unconventional technique. According to the low radiance received from the stratosphere noise has also to be taken into account, especially in case of single non- coadded spectra. Therefore an advanced statistical method was investigated to derive the phase of the interferogram by minimizing the correlation of the real and imaginary part of the spectrum as well as the variance of the imaginary part (the beamsplitter spectrum). The complete processing and calibration scheme of the FTS-emission sounder will be presented focusing on a detailed description of phase behavior due to the beamsplitter emission and of the correction process.

The Ozone Dynamics Ultraviolet Spectrometer (ODUS) is a satellite-borne, nadir-looking ultraviolet spectrometer for measuring total ozone amount. It will be launched in 2005 onboard Japanese earth observation satellite GCOM-A1. The ODUS instrument measures continuous spectrum from 306 to 420 nm with 0.5 nm spectral resolution and 20 km spatial resolution, using an Ebert-type polychromator and a one-dimensional silicon CMOS array detector, which will improve the accuracy of the retrieved total ozone amount. We have completed the conceptual design of system, and manufactured and tested the laboratory model of the detector and the optical assembly. We have succeeded in developing a detector with sufficient sensitivity and a polychromator with little stray light. We have also confirmed the optical performance and evaluated the detailed wavelength structure of the instrument function. This paper presents an overview of the ODUS instrument, the summary of the evaluation results of the laboratory models.

Development of space-qualified Fourier Transform Spectrometer (FTS) systems for long-life operational space missions requires development of new technologies. ITT Industries has been developing these new FTS technologies for the past 5 years, in anticipation of their use in FTS systems for operational meteorological satellites and other long-life space applications. Our objectives are to identify FTS technologies that have important mission advantages, design and build new components using these technologies, and prove the new technologies in a complete FTS interferometer technology testbed. This paper describes the process used at ITT to identify and develop these new technologies, the Dynamically Aligned Porch Swing (DAPS) interferometer technology testbed used to prove the new technologies, characterization tests of the DAPS used to verify the performance of the new technologies, and space qualification efforts now underway to verify that the new technologies can survive space environments.

The systems engineering aspects of evolving and developing the optimal design for Fourier transform interferometers are presented in this paper. A Fourier transform spectrometer (FTS) is a versatile electro-optical sensor for remote sensing, hyperspectral imaging, and laboratory chemical kinetics. Principal features include broad spectral coverage and high spectral resolution (Fellgate advantage) and high throughput (Jacquinot advantage). Due to its versatility, across various requirements, e.g. (resolution, bandwidth and aperture) sensor architecture contains an N-dimensional parametric trade matrix that needs to be readily assessed. Specifically considered are the logical steps utilized to flow down primary (customer) requirements and specifications to secondary (derived) requirements. Configurational aspects, generic trades, and parametric selections are emphasized for non-imagers as well as for imaging FTS. With an appropriately designed robust sensor, the noise equivalent spectral radiance or NE(Delta) N performance will be largely dictated by the scene and the instrument background flux. The performance will not be dictated by noise terms associated with interferogram encoding and signal handling. The mathematical formalism of interferometric error source types and photon limited design expressions are presented. The composition of these expressions are examined from the points of view of optical band limiting and some useful trade rules parametrically relating scan time and S/N to spectral resolution. For a well designed and executed interferometer, typical performance data are presented in terms of modulation index, calibrated radiometric atmospheric spectral signatures, and atmospheric spectral signatures for two spectral resolutions.

This paper will present measured reflectance, transmittance, surface figure and roughness data for KBr and ZnSe beamsplitters and compensators that were made for use on spaceflight Michelson-type Fourier transform spectrometers. Measured data for visible and infrared wavelengths, at room temperature and cryogenic temperatures, will be shown. Calculated performance data for KCl substrates will be included for comparison.

This paper describes the Mars 2001 Miniature Thermal Emission Spectrometer (Mini-TES) being built by Raytheon Santa Barbara Remote Sensing (SBRS) under contract to Arizona State University (ASU). Mini-TES is a point (single-pixel) Fourier Transform Spectrometer (FTS), covering the spectral range 5 - 28 microns (micrometer) at 10 cm^-1 spectral resolution. It is part of the Athena Precursor Experiment (APEX) that will fly to Mars on board NASA's Mars 2001 Lander mission. Mini-TES is designed to provide a key mineralogical remote sensing component of the APEX mission, which includes several other science instruments. Even though Mini-TES is a new design, the Athena mission required proven, flight-tested instrumentation to meet a two-year development schedule. Therefore, SBRS designed Mini-TES based on proven heritage from the successful Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES), which was launched in 1996 and is currently providing excellent science data from the MGS, in orbit about Mars. Mini-TES occupies only 15% of the volume and is 83% lighter than MGS TES, yet nearly all the design and technology elements of Mini-TES are direct descendants of proven flight components from MGS TES. Relevance of the Mini- TES to APEX science, overall design, performance, as well as details of the hardware being fabricated at SBRS, are discussed. Possible applications to future missions are also addressed.

An advanced compact differential absorption lidar detection system for atmospheric water vapor measurement is reported. This system interfaces the lidar receiver telescope to a personal computer and contains an advanced avalanche photodiode detector, signal conditioning circuit, 14-bit, 10 MHz digitizer and a microcontroller. The whole system was realized on one electronic card. Characterization results indicate low noise with reduced size, reduced mass and an extended measurement range over current lidar detection systems. The new system can be incorporated in spacecraft lidar systems. Simulated lidar return measurements were performed with the new system in order to obtain its minimum detectable signal limits.

The Stratospheric Aerosol and gas Experiment III (SAGE III) is part of the NASA EOS program designed for long term monitoring of atmospheric ozone and aerosol, together with other atmospheric species important to the study of global change. SAGE III is an advanced version of the previous occultation instruments such as SAM II, SAGE I, and SAGE II which have provided long term data on aerosol and ozone for the last twenty years. SAGE III will continue these long term measurements well into the first decade of the 21st century. SAGE III will measure profiles of aerosols, ozone, water vapor, nitrogen dioxide, temperature, pressure, chlorine dioxide, and nitrogen trioxide using the solar and lunar occultation techniques. Currently two SAGE III instruments will be launched between 1999 and 2003. The First SAGE III will be on a Russian Meteor 3M spacecraft to be launched in the Fall of 1999. The second SAGE III will be on the Space Station in 2003.

The SAGE III instrument design, and sampling modes are presented. The central focus will be on the instrument test data useful for characterization and their relevance to processing algorithms. The following effects will be discussed: spectrometer stray light and 'line spread;' CCD substrate scattering into the readout registers; dark current; charge transfer efficiency; wavelength calibration; and etaloning. Test data from Sun/Moon-Look testing from all three instruments will be presented.

The instrument description and ground test simulations of on- orbit scenarios for the Stratospheric Aerosol and Gas Experiment III (SAGE-III) are presented. SAGE-III is a spectrographic instrument that has been developed in the U.S. and will orbit aboard a Russian Meteor-3M spacecraft beginning Fall of 1999. It will orbit at a nominal altitude of 1020 km and inclination of 99.6 degrees for global coverage. The instrument will measure the attenuated solar and lunar radiation from 290 nm to 1550 nm wavelength range through the stratosphere. The radiant data are normalized to the non- attenuated radiation measured above the atmosphere during each occultation event. The data are used to calculate the vertical distribution of stratospheric aerosols, ozone and other species that are critical in studying trends and global change. After on-orbit operations being, the autonomy of the instrument will not need up-link commands to acquire science data or to transmit the data back to the United States and Russia.

SAGE III is the latest version of the successful Stratospheric Aerosol and Gas Experiment instruments that have been launched over the last 21 years. Three instruments have been completed for launch on various platforms over the next few years. This paper summarizes some of the more difficult performance characteristics and many of the lessons learned in building up the spectrometer/telescope.

A detailed discussion on the inversion algorithm developed by the Laboratoire d'Optique Atmospherique, University of Lille, France, for the analysis of the Stratospheric Aerosol and Gas Experiment III (SAGE III) solar occultation data is presented. The scope of the paper is limited to nitrogen dioxide, ozone and aerosol retrieval. The forward model algorithm for calculating atmospheric transmittances in the two SAGE III solar channels, at 440 nm and at 600 nm, is presented. Then the inversion algorithm is introduced, accomplished in two sequential steps: the first one is the spatial inversion of the simulated slant optical thickness profile to obtain the extinction coefficient profile and the second is the spectral inversion of the extinction coefficient at each altitude to separate gas and aerosol contributions by using a least squares method over the spectral signatures. Error analysis is also discussed: the results of this analysis indicate regression error of 1% or less in the aerosol retrieval, of 0.1% or less for the ozone retrieval and of about 0.1% for the nitrogen dioxide retrieval. The paper also discuss on the correlation between the relative differences and the relative contribution of the considered constituents in the total extinction coefficient and then can determine the inversion algorithm's performances.

The occultation experiment SAGE III (Stratospheric Aerosol and Gas Experiment III) is expected to be launched in Autumn 1999. The instrument will be on board the satellite 'Meteor 3M' on a polar orbit. This experiment is based on the same principle than SAGE II. However some channels are divided in some subchannels. For example it is the case of nitrogen dioxide channel at 430 - 450 nm, ozone at 560 - 624 nm and water vapor at 933 - 960 nm. On the other hand the lunar occultation is added in order to detect minor components: OClO, NO₃. A simulation of the transmissions for only the channel devoted to the water vapor has been done, from a water vapor profile obtained for a SAGE II event. The wavelength range 933 - 960 nm is planned to be divided in thirty subchannels. The inverted profiles of water vapor obtained in each subchannel are compared to the input profile. The relative difference between the mean retrieved profile and the data is smaller than 15%.

An overview of joint Russian-American mission operations for the Meteor-3M/SAGE III mission is presented. The Russian Space Agency is responsible for the operation and sustaining engineering of the Meteor-3M spacecraft. The SAGE III mission operations center located at the NASA Langley Research Center is responsible for instrument operation, sustaining engineering, Level 0 data processing, and orbit determination. SAGE III science data is received at ground stations located at the NASA Wallops Flight Facility and in Russia using redundant, twice daily, data playbacks. The highly autonomous mission design requires a high degree of payload autonomy. A combination of navigation data provided by the spacecraft's GPS/GLONASS receiver and novel on-board event scheduling software is used to schedule routine occultation measurements without the need for ground commanding.

This paper presents the SAGE III mission for the International Space Station. SAGE III is fifth in a series of instruments developed to monitor aerosols and gaseous constituents in the stratosphere and troposphere. Three instruments are being developed by the National Aeronautics and Space Administration (NASA) Langley Research Center for the Earth Science Enterprise: one for a high-inclined orbit aboard the Russian Meteor-3M (M3M) spacecraft; one for a mid-inclined (51.6 deg) orbit on the International Space Station, the subject of this paper; and a third for a potential flight of opportunity (FOO) mission. The SAGE III/ISS payload is comprised of international components: a pointing platform called the Hexapod, provided by the European Space Agency and the Expedite the Processing of Experiments to International Space Station (ISS) (EXPRESS) pallet adapter, (part of a carrier system to be built by Brazil for NASA. The SAGE III/ISS mission is manifested for a launch on the ISS Utilization Flight (UF) 3, currently scheduled to launch February 2003.

The Stratospheric Aerosol and Gas Experiment (SAGE) III requires a detector that provides spectral coverage from 280 - 1050 nm. In order to achieve higher responsivity at the ultra-violet wavelengths a backside-thinned silicon CCD technology was chosen. For strength, the backside-thinned detector was bonded to a soda glass substrate. The device thinness allowed the long near infrared wavelengths to pass through the silicon, scatter off the soda glass, and cause cross talk into nearby pixels. Reflections from the soda glass caused etalon-like effects and gave the thinned CCD a highly temperature dependent response. These difficulties led the project manager to examine different options for a replacement detector. Photodiode/CCD technology based on the Moderate- Resolution Imaging Spectrometer-Tilt (MODIS-T) and Gas and Aerosol Monitoring Sensorcraft (GAMS) detectors systems was combined and used to design and fabricate a backup detector for the SAGE III program. The device design and characterization are presented. The design focused on elimination of the scattering due to the soda glass and the temperature dependent etalon effect, increasing charge storage capacity. The detector was designed to allow a retrofit with the existing SAGE III spectrometer. The primary disadvantage of the new detector is its loss of responsivity at the shorter wavelengths.

Monitoring tropospheric chemistry from space is the next frontier for advancing present-day remote sensing capabilities to meet future high-priority atmospheric science measurement needs. Paramount to these measurement requirements is that for tropospheric ozone, one of the most important gas-phase trace constituents in the lower atmosphere. Such space-based observations of tropospheric trace species are challenged by the need for sufficient horizontal resolution to identify constituent spatial distribution inhomogeneities (that result from non-uniform sources/sinks and atmospheric transport) and the need for adequate temporal resolution to resolve daytime and diurnal variations. Both of these requirements can be fulfilled from a geostationary Earth orbit (GEO) measurement configuration. An advanced atmospheric remote sensing concept for the measurement of tropospheric ozone from a GEO-based platform is presented. The concept is centered about an imaging Fabry-Perot interferometer (FPI) observing a narrow spectral interval within the strong 9.6 micron ozone infrared band with a spectral resolution approximately 0.07 cm^-1. This concept could also simplify other atmospheric chemistry sensor designs (which typically require spectral resolutions in the range of 0.01 - 0.1 cm^-1), since such an FPI approach could be implemented for those spectral bands requiring the highest spectral resolution and thus simplify overall design complexity.

The NASA sponsored Advanced Geosynchronous Studies (AGS) program is to conduct intensive studies to demonstrate the use of advanced new technologies and instruments on geosynchronous satellites to improve our current capabilities of monitoring the global weather, climate, and chemistry. The Geostationary Atmospheric Sounder (GAS), to be developed under AGS, is intended to demonstrate a new space-based infrared imaging interferometer that is well suited for achieving the high temporal and spatial global coverage of cloud motion, water vapor transport, thermal and moisture vertical profiles, land and ocean surface temperature, and trace gas concentrations. The AGS technology demonstrations will show the capabilities of passive infrared observations from future NOAA geostationary operational sounders. The focus of this presentation is to provide quantitative assessments of a few design configurations for the trace gases sounding feasibility from geostationary orbit. Trade-off studies of spectral, temporal, and spatial resolution are to be emphasized. Preliminary conclusions for the design of an operational geo sounder for chemistry applications will be made.

Wedge Imaging Spectrometer (WIS) technology promises advantages in lower size, cost, and sensor complexity but requires consideration of the effects of non-simultaneous collection of spectral information. Space applications appear particularly matched to the characteristics of this technology. Examples of WIS imagery collected by airborne acquisition systems have been used to assess the utility of WIS space imagery. Recent hardware development efforts have produced sensor components amenable to hyperspectral space applications in the Visible-Near-Infrared, Short Wavelength Infrared, Short-Mid Wavelength Infrared, and Long Wavelength Infrared bands. These components demonstrate excellent performance and provide the basis for space instrument concepts that utilize the inherent simplicity, compactness, and economy of the wedge spectrometer technology.

Imaging spectrometry from geostationary earth orbit (GEO) can provide the frequently-refreshed detailed information on physical properties of earth's atmosphere and surface needed to enable critical new science missions and ultimately improve operational weather forecasting. We describe and evaluate a concept for imaging spectrometry from GEO that addresses both traditional imaging and sounding applications. Our Geostationary Wedge-filter Imager-Sounder (GWIS) uses spatially variable wedge filter spectrometers to collect earth radiance with approximately 2 km resolution over a 710 - 2900 cm^-1 (3.45 - 14.0 micrometer) spectral range at 1% spectral resolution. The resulting instrument, based on LWIR and MWIR wedge spectrometer technology recently developed by Raytheon, is a compact, rugged imager-sounder with better sensitivity, spectral resolution, spatial resolution and full disk coverage time than the current multispectral GOES imager. GWIS sounding performance was simulated by evaluating retrieval performance with respect to a global database of 119,694 cloud-free samples using a stepwise regression algorithm. Retrieved atmospheric parameters included surface air temperature, surface skin temperature, surface water vapor, total precipitable water vapor, total ozone and vertical profiles of temperature and water vapor. In all cases, GWIS outperformed the current GOES sounder. Furthermore, GWIS RMS error performance approached that of advanced higher spectral resolution sounders (e.g., 1.2 K/1 km for GWIS versus 1 K/1 km for advanced sounders). Due to its higher spatial resolution and more complete spatial coverage, GWIS achieves this high quality cloud free sounding performance roughly two times more frequently than high spectral resolution advanced sounders. Combining this new technology with proven wedge spectrometer approaches for visible and near-infrared wavelengths would provide imaging- sounding data from GEO with unprecedented detail and fidelity for a wide range of weather, climate, land use, ocean color and other earth science studies.

A unifying theme throughout the ESE science objectives is the identification of regions with large temporal and spatial gradients. Severe storm formation occurs in the boundary regions between airmasses with very different temperatures, pressures, water content, aerosol loading. Severe storm tracking and forecasting utilizes the discontinuities in observed fields and gradient fields to diagnose and forecast the formation, evolution, and motion of severe storms. In a similar fashion, heat islands, super-regional pollution, and rain shower formation are each the result of temporal and spatial gradients present in the atmosphere. Diagnosing and forecasting these events requires an ability to map atmospheric gradients and discontinuities in real-time on micro to meso-scales in the atmosphere (0.5 - 500 km). A new measurement concept, the Imaging Fourier Transform Spectrometer (IFTS) is capable of demonstrating a class of autonomous event identification, monitoring and tracking sensors. In order to provide this capability a sensor with the ability to combine high spatial resolution (0.5 - 1 km) imaging with high spectral resolution (0.25 cm - 1 across the mid infrared 3 -10 microns) in time intervals of a few seconds is required. An electronically programmable infrared camera that combines a large-format focal plane array with a Fourier transform spectrometer can deliver this capability. It also builds on currently fielded airborne demonstration systems and an instrument concept in development for the Next Generation Space Telescope (NGST). The IFTS concept is revolutionary in several aspects. It can produce 2 - 10 fold increase in spatial resolution, 2 fold increases in spectral resolution, and 30 fold increases in temporal resolution. In combination the measurement concept would require a 100 - 600 fold increase in telemetry bandwidth without a new approach to imaging. IFTS breaks this paradigm with a new approach to hyperspectral imaging. Severe storm forecasting requires gradient fields (i.e., first and second derivatives of atmospheric observations). Hence, this measurement concept for IFTS is enabled by four innovations: (1) directly observe the derivative fields, (2) Nyquist sample the image plane to enable full utilization of the telescope performance, (3) have multi-channel detection of gradient regions, and (4) provide an autonomous targeting and tracking system that identifies, subsets, and follows regions with significant discontinuities (i.e., regions where severe storms, toxic pollution, heat islands, or rain/thunderstorms will form).

The Thermosphere (DOT) Ionosphere (DOT) Mesosphere (DOT) Energetics and Dynamics (TIMED) spacecraft being developed by The Johns Hopkins University Applied Physics Laboratory is the first mission in NASA's Solar Connections program. TIMED is a low-cost mission aimed at providing a basic understanding of the least explored and least understood region of the earth's environment, the atmospheric band extending from 60 to 180 kilometers in altitude. The TIMED suite of instruments is intended to determine the temperature, density, and wind structure in the Mesosphere, Lower Thermosphere and Ionosphere (MLTI) region including seasonal and latitudinal variations. TIMED is also intended to determine the relative importance of radiative, chemical, electrodynamic, and dynamic sources and sinks of energy for the thermal structure of the MLTI. This paper provides an overview of the TIMED mission, discussing science objectives, mission architecture, spacecraft and ground system design, and the decoupled mission operations concept. The focus of this discussion will be on cost reduction efforts, especially those related to advanced technology. This paper also provides a brief introduction to the four TIMED instruments (GUVI, SABER, SEE, and TIDI) and develops a context for understanding their common design elements.

The Solar EUV Experiment (SEE) on the NASA Thermosphere, Ionosphere, and Mesosphere Energetics and Dynamics (TIMED) mission will measure the solar vacuum ultraviolet (VUV) spectral irradiance from 0.1 to 200 nm. To cover this wide spectral range two different types of instruments are used: a grating spectrograph for spectra between 25 and 200 nm with a spectral resolution of 0.4 nm and a set of silicon soft x-ray (XUV) photodiodes with thin film filters as broadband photometers between 0.1 and 35 nm with individual bandpasses of about 5 nm. The grating spectrograph is called the EUV Grating Spectrograph (EGS), and it consists of a normal- incidence, concave diffraction grating used in a Rowland spectrograph configuration with a 64 X 1024 array CODACON detector. The primary calibrations for the EGS are done using the National Institute for Standards and Technology (NIST) Synchrotron Ultraviolet Radiation Facility (SURF-III) in Gaithersburg, Maryland. In addition, detector sensitivity and image quality, the grating scattered light, the grating higher order contributions, and the sun sensor field of view are characterized in the LASP calibration laboratory. The XUV photodiodes are called the XUV Photometer System (XPS), and the XPS includes 12 photodiodes with thin film filters deposited directly on the silicon photodiodes' top surface. The sensitivities of the XUV photodiodes are calibrated at both the NIST SURF-III and the Physikalisch-Technische Bundesanstalt (PTB) electron storage ring called BESSY. The other XPS calibrations, namely the electronics linearity and field of view maps, are performed in the LASP calibration laboratory. The XPS and solar sensor pre-flight calibration results are primarily discussed as the EGS calibrations at SURF-III have not yet been performed.

The Global Ultraviolet Imager (GUVI) on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission will determine the variability in thermospheric composition, and its response to auroral inputs as well as measuring those inputs. GUVI is the result of twenty years of work in designing large field of regard far ultraviolet (110 - 180 nm) imagers for spaceflight. These systems are based on the concept of a horizon-to-horizon 'monochromatic' imager. The field of view of a spectrograph is swept from horizon to horizon using a scan mirror. The spectrograph uses a grating to spectrally disperse the light. A two-dimensional detector is used to record spatial and spectral information simultaneously. Images are obtained at discrete wavelengths without the use of filters; this reduces if not eliminates much of the concern about instrumental bandpasses, out-of-band rejection, and characterization of filter responses. Onboard processing is used to bin the spectral information into 'colors' thereby reducing the overall data rate required. The spectral bandpass is chosen to lie in the far ultraviolet so that the sunlit and dark aurora can be imaged. We review the instrument's as delivered performance and the TIMED science requirements. TIMED will be launched May 18, 2000 and will inaugurate the Solar-Terrestrial Connections program at NASA.

The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) experiment is one of four experiments that will fly on the Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics (TIMED) mission to be launched in May 2000. The primary science goal of SABER is to achieve major advances in understanding the structure, energetics, chemistry, and dynamics, in the atmospheric region extending from 60 km to 180 km altitude. This will be accomplished using the space flight proven experiment approach of spectral broadband limb emission radiometry. SABER will scan the horizon in 10 selected bands ranging from 1.27 micrometer to 17 micrometer wavelength. The observed vertical horizon emission profiles will be processed on the ground to provide vertical profiles with 2 km altitude resolution, of temperature, O₃, H₂O, and CO₂; volume emission rates due to O₂(¹(Delta) ), OH((upsilon) equals 3,4,5), OH((upsilon) equals 7,8,9), and NO; key atmospheric cooling rates, solar heating rates, chemical heating rates, airglow losses; geostrophic winds, atomic oxygen and atomic hydrogen. Measurements will be made both night and day over the latitude range from the southern to northern polar regions. The SABER instrument uses an on-axis Cassegrain design with a clam shell reimager. Preliminary test and calibration results show excellent radiometric performance.

The TIMED Doppler Interferometer (TIDI) is a Fabry-Perot interferometer designed to measure winds, temperatures, and constituents in the mesosphere and thermosphere (60 - 300 km) region of the atmosphere as part of the TIMED mission. TIDI is a limb viewer and observes emissions from OI 557.7 nm, OI 630.0 nm, OII 732.0 nm, O₂(0-0), O₂(0-1), Na D, OI 844.6 nm, and OH in the spectral region 550 - 900 nm. Wind measurement accuracies will approach 3 ms^-1 in the mesosphere and 15 ms^-1 in the thermosphere. The TIDI instrument has several novel features that allow high measurement accuracies in a modest-sized instrument. These include: an optical system that simultaneously feeds the views from four scanning telescopes which are pointed at plus or minus 45 degrees and plus or minus 135 degrees to the spacecraft velocity vector into a high-resolution interferometer, the first spaceflight application of the circle-to-line imaging optic (CLIO), and a high quantum efficiency, low noise CCD.

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) densities, and stratospheric aerosol extinctions coefficients, are also retrieved. The instrument characteristics have been carefully monitored by frequent calibrations during the nearly eight years of operation. The instrument sensitivity showed a significant decrease (close to 50% in some cases) during the first seven and a half years of operation which was caused by the piezoelectric-controlled etalons slowly drifting from a parallel state. A recalibration of the etalons in late 1998 resulted in close to a complete recovery of the instrument sensitivity. The loss of sensitivity was linear with time, with discrete changes occurring at times. Careful modeling of the data permits a determination of the sensitivity as a function of time, allowing the data to be corrected for this systematic effect.

The night-time temperature in the altitude region from 90 to 120 km is known to be characterized by a steep gradient caused by heating due to ultraviolet absorption of sunlight in the middle thermosphere during the day, yet measurements of this gradient are scarce. Remote optical sensing methods fail in this region because the few nightglow emissions above 100 km are contaminated by photochemical reaction energy. We address this measurement by considering the scattered return signal from a laser emitting horizontally from a rocket as it traverses the region. Two analyses are presented. The ideal method consists of measurement of the Raman rotational spectrum of the combined N₂ and O₂ back-scattered signals by means of interference filter spatial spectral scanning. A quantitative estimate of such a measurement shows that this method, while only marginally practical at the moment, holds significant promise. The second method consists of measuring the back-scattered Rayleigh signal, which is a thousand times brighter, and deducing the temperature from the density scale height. This measurement is shown by quantitative precision estimates to be practical using today's technology. Proposed optical configurations for both methods are presented, and the limitations of both are explored.

Large gains in the sensitivity of Fabry-Perots for geocoronal research have been achieved at the University of Wisconsin employing the technique of CCD annular summing spectroscopy. Earlier 'demonstration observations' of this technique lead to a significant new understanding of geocoronal hydrogen excitation. This paper will outline a new ground-based observing program which is building on these earlier observations in order to obtain definitive data regarding the physical processes which govern the abundance and transport of atomic hydrogen in the earth's atmosphere. Two double-etalon Fabry-Perot spectrometers have been installed at the University of Wisconsin's Pine Bluff Observatory (WI) for the purpose of making a systematic series of high spectral resolution (R approximately equals 100,000) line profile, and intensity observations of geocoronal hydrogen nightglow. For the first time it will be possible to obtain coincident observations of geocoronal hydrogen Balmer-alpha and Balmer- beta with sufficient signal-to-noise for detailed line profile studies. Because the geocoronal Balmer-beta emission is about one tenth the intensity of Balmer-alpha, the fitness of this line has frustrated past attempts to determine its profile; however, gains in sensitivity afforded by the annular-summing technique make these new observations possible. It is anticipated that these simultaneous observations will provide a means by which to isolate previously observed perturbations to the Balmer-alpha line, the components of which may arise from both contributions due to quantum mechanical fine structure and the non-Maxwellian dynamics of the hydrogen exosphere. Each of these instruments employs the annular summing technique in which the Fabry-Perot's annular fringe pattern is imaged onto a low noise CCD chip. Using the property that equal area annuli correspond to equal spectral intervals, software is used to divide the CCD image into equal area annular bins, whereby the Fabry-Perot interference pattern is converted into a useful spectral profile. This paper will describe the instrumentation, and how it relates to the planned observational program.

Spatial heterodyne spectroscopy (SHS) is a relatively new and incompletely developed method of Fourier transform spectroscopy that has advantages over conventional FTS in certain applications. In the SHS instrument, diffraction gratings replace the flat mirrors used in each arm of a conventional Michelson, and an imaging detector is used at the output to record a spatially heterodyned interferogram without any scanning elements. The mechanical simplicity of a diffraction grating is combined with the high light-gathering power of interference spectrometers. SHS systems can achieve an additional light-gathering gain of about two orders of magnitude over conventional FTS or Fabry-Perot interference spectrometers by field-widening using fixed transmitting wedges. Compared to conventional instruments, these gains translate into smaller instruments and/or higher sensitivity for a specified application. Flatness defects in the optics can largely be corrected in software, leading to relaxed tolerances which simplify extension to short wavelengths. This paper focuses on the concepts used in the design of an SHS for mesospheric OH remote sensing at 308 nm, and their validation in laboratory testing. A field-widened system has been constructed, and will soon undergo performance tests with an eye towards space application in the relative near future. Compared to a conventional grating spectrograph used previously for OH measurements, the SHS system is designed to achieve higher resolving power and several times more sensitivity in 1/10 or less of the volume, and with no moving parts.

MODTRAN4, the latest publicly released version of MODTRAN, provides many new and important options for modeling atmospheric radiation transport. A correlated-k algorithm improves multiple scattering, eliminates Curtis-Godson averaging, and introduces Beer's Law dependencies into the band model. An optimized 15 cm^-1 band model provides over a 10-fold increase in speed over the standard MODTRAN 1 cm^-1 band model with comparable accuracy when higher spectral resolution results are unnecessary. The MODTRAN ground surface has been upgraded to include the effects of Bidirectional Reflectance Distribution Functions (BRDFs) and Adjacency. The BRDFs are entered using standard parameterizations and are coupled into line-of-sight surface radiance calculations.

Radiance multiply scattered from clouds and thick aerosols is a significant component in the short wave IR through the visible region of the electro-optical (EO) spectrum. In MODTRAN, until very recently, multiple scattering predictions could not vary with the azimuth of the line-of-sight (LOS), although the single scattering component of the radiance did take the azimuthal variation into account. MODTRAN has now been upgraded to incorporate the dependence of multiple scattering (MS) on the azimuth of the LOS. This was accomplished by upgrading the interface between MODTRAN and DISORT, which is used as an MS subroutine in MODTRAN. Results from the upgraded MODTRAN are compared against measurements of radiance in a cloudy sky in the 1.5 - 2.5 micrometer region. Furthermore, taking advantage of DISORT, the upgraded version of MODTRAN can accommodate parameterized BRDFs (Bi-Directional Reflectance Distribution Functions) for surfaces. Some results, which demonstrate the new MODTRAN capabilities, are presented. Additionally, MS results from MODTRAN are compared to results obtained from a Monte-Carlo model.

Atmospheric emission, scattering, and photon absorption degrade spectral imagery data and reduce its utility. We report on the use of an atmospheric compensation code for the visible and near-infrared, based on MODTRAN 4, that includes spectral analysis, accounts for interference to a given pixel by adjacent pixels, and provides a polishing routine to clear residual atmospheric spectral features common to a group of pixels. A NASA/JPL AVIRIS data sample is analyzed.

Scattered solar radiance from cirrus clouds has traditionally been detected over land at 1.37 micrometer, a wavelength that is ordinarily opaque to the surface due to water vapor absorption. We describe a new pairwise regression method for spectral imagery that retrieves cloud signals in the vicinity of a partially transmitting band, such as the 1.13 micrometer band, over any type of spatially structured terrain. The method, which uses spatial filtering and linear regression to cancel the surface background, has been applied to several rural and urban AVIRIS scenes. With a single cloud or cloud layer in the scene, the 1.13 micrometer and 1.37 micrometer cloud signals are closely correlated. Since the two signals are absorbed differently by water vapor, the slope of the correlation plot indicates the column water vapor above the cloud and thus the approximate cloud altitude. The less strongly absorbed 1.13 micrometer signal is closely related to the cloud optical thickness and can be used by itself or in combination with the 1.37 micrometer signal to correct apparent surface reflectance spectra for cirrus cloud effects.

Using NOAA-14 AVHRR satellite imagery and ground-based aerosol optical thickness ((tau) ) measurements, the single scattering albedo ((omega) ₀) of biomass burning aerosols is estimated for selected days during the Smoke, Clouds and Radiation- Brazil (SCAR-B) experiment held in Brazil during 1995. The retrieved average aerosol single scattering albedos at 0.55 micrometer over the study areas range between 0.83 to 0.92 which is in good agreement with in situ measurements and previous studies. The uncertainty in the retrieved (omega) ₀ due to the uncertainties in clear sky albedos and observed AVHRR reflectance is examined. When (tau) at 0.55 micrometer is smaller than 1.0, the retrieved (omega) ₀ is sensitive to the assumed clear sky albedo values. When (tau) at 0.55 micrometer is larger than 2.0 , the retrieved (omega) ₀ is less sensitive to clear sky albedos. This study shows that when ground-based aerosol (tau) is available, (omega) ₀ can be retrieved to within 0.06 which could then be used to characterize biomass burning aerosols in radiative transfer calculations.

The potential for using Geostationary Operational Environmental Satellite (GOES) Sounder radiance measurements to monitor total atmospheric ozone is examined. A statistical regression using GOES channel 1 (14.7 micrometer), 2 (14.4 micrometer), 3 (14.1 micrometer), 4 (13.6 micrometer) and 9 (9.7 micrometer) radiances, followed by a physical iterative retrieval using only the channel 9 radiance, allows retrieval of total atmospheric ozone. Simulations show that the algorithm is suitable for retrieving total ozone with reasonable accuracy. In addition, GOES retrieved ozone values are compared with Total Ozone Mapping Spectrometer (TOMS) ozone measurements from the Earth Probe (EP) satellite. Both qualitative and quantitative comparisons show that GOES retrievals are able to capture most of the main features of the ozone distribution. Because of the high temporal and spatial density provided by GOES Sounder measurements, the potential uses of GOES ozone retrievals and associated products is exciting.

The Measurements Of Pollution In The Troposphere (MOPITT) instrument will monitor the global concentrations of carbon monoxide and methane. It will be flown on the Earth Observing Satellite, Terra (EOS-AM1), scheduled for launch late in 1999. This paper describes the proposed early mission operations of MOPITT.

This paper will serve as an overview of the challenges to the recovery of information on atmospheric CO and CH₄ from the measurements made by the MOPITT instrument that has been described by Drummond et al. It will also provide a context and introduction to several of the following papers that go into greater detail on particular topics, and outline plans for the data processing. Here we briefly outline the principles of correlation radiometry as used by MOPITT, and introduce the principles behind the retrievals. After noting plans for data processing, we discuss our approach to data validation, and the ability to see global distributions of CO in the MOPITT data.

The Measurements Of Pollution In The Troposphere (MOPITT) instrument will monitor the global concentrations of carbon monoxide and methane. It will be flown on the Earth Observing Satellite, EOS-AM1, scheduled for launch late in 1999. This paper primarily describes the pre-flight testing conducted at the University of Toronto, Instrument Characterization Facility (ICF) and will also very briefly describe testing, post integration to the spacecraft at the Lockheed Martin, Valley Force integration and test facility and at the Vandenburg launch site.

The Measurements Of Pollution In The Troposphere (MOPITT) instrument will monitor the global concentrations of carbon monoxide and methane. It will be flown on the Earth Observing Satellite, EOS-AM1, scheduled for launch late in 1999. This paper describes the analysis of a twenty four hour data set that was recorded during the latter stages of testing at the University of Toronto Instrument Characterization Facility (ICF). This data set represents the best 'near real time' contiguous data available and it is being used to help understand the instrument behavior and characteristics, as well as with algorithm development with the goal of the University of Toronto team being to determine the gain, offset and noise parameters for all channels from the in-flight calibration system.

The MOPITT (Measurement of Pollution in the Troposphere) instrument, to be launched on the Earth Observing System Terra platform, employs gas-correlation spectroscopy to measure profiles of tropospheric carbon monoxide and the total column of methane. The modeling of the instrument, and the associated radiative transfer, comprise the forward model employed in the retrieval calculations. The MOPITT forward model has been implemented through a hierarchy of radiation codes whose salient features are reviewed here.

The Measurement of Pollution in the troposphere (MOPITT) instrument is an eight-channel gas correlation radiometer to be launched on the Earth Observing System (EOS) Terra spacecraft in 1999. Its main measurement objectives are tropospheric carbon monoxide (CO) profiles and total column. This paper gives a detailed description of MOPITT CO retrieval algorithm, which derives total CO column and tropospheric CO mixing ratios at a number of atmospheric pressure levels from MOPITT radiance observations. Retrieval performance evaluation using simulated MOPITT data are discussed.

Tropospheric concentrations of methane have been increasing at a rate of approximately 1%/year, though recent measurements suggest some slowing in this trend. Increased concentrations of methane, a greenhouse gas, will have significant consequences for tropospheric chemistry and climate on a global scale. Characterization of the spatial and temporal variability of methane is one goal of the MOPITT (Measurement of Pollution In The Troposphere) instrument included on the EOS Terra satellite. This instrument includes spectral channels designed to measure methane total column with approximately 1% precision with a spatial resolution of approximately 22 X 22 km. Retrieval of the methane total column will be accomplished by the MOPITT instrument from measurements of solar radiation reflected at the earth's surface. Gas correlation radiometry will be used to separate the spectral signature of methane in the upwelling radiance from features produced by other trace gases. The retrieval algorithm is based on maximum likelihood and uses an initial guess profile and methane total column variance estimates provided by aircraft in-situ measurements. In this talk, we will describe features of the retrieval algorithm in detail and present results of retrieval simulations conducted to test the sensitivity of the retrieval algorithm to various sources of error.

The Measurement Of Pollution In The Troposphere (MOPITT) instrument, which will be launched on the Terra spacecraft, is designed to measure the tropospheric CO and CH₄ at a nadir-viewing geometry. The measurements are taken at 4.7 micrometer in the thermal region, and 2.3 and 2.2 micrometer in the solar region for CO mixing ratio retrieval, CO total column amount and CH₄ column amount retrieval, respectively. To ensure the required measurement accuracy, it is critical to identify and remove any cloud contamination to the channel signals. In this study, we develop an algorithm to detect the cloudy pixels, to reconstruct clear column radiance for pixels with partial cloud covers, and to estimate equivalent cloud top positions under overcast conditions to enable CO profile retrievals above clouds. The MOPITT channel radiances, as well as the first guess calculations, are simulated using a fast forward model with input atmospheric profiles from ancillary data sets. The precision of the retrieved CO profiles and total column amounts in cloudy atmospheres is within the expected plus or minus 10% range. Validations of the cloud detecting thresholds with MODIS Airborne Simulator (MAS) data and MATR (MOPITT Airborne Test Radiometer) measurements are also carried out and will be presented separately.

The Measurements Of Pollution In The Troposphere (MOPITT) experiment will measure the amount of methane and carbon monoxide in the Earth's atmosphere utilizing spectroscopy in the near Infrared (IR) (2.2, 2.3, and 4.7 micrometer). In this wavelength region, clouds confound the retrieval of methane and carbon monoxide by shielding both the surface and atmospheric emission below the clouds from MOPITT. A technique has been developed to detect cloudy pixels, and an algorithm has been developed to estimate clear sky radiance from cloud contaminated pixels. This process is validated using images from the MODIS Airborne Simulator (MAS). MAS images are comprised of 50 m pixels in comparison to the larger 22 km MOPITT pixels. We aggregate the higher resolution MAS data to simulate MOPITT pixels. The aggregation is analyzed for clear and cloudy conditions and a cloud fraction is calculated. The aggregate is then averaged to recreate the scene that MOPITT would have seen. The cloud detection algorithms are applied to the degraded MAS image. The results are compared to validate the techniques imbedded in the standard MOPITT processing stream.

The Measurements of Pollution in the Troposphere-Aircraft (MOPITT-A) instrument is being constructed at the University of Toronto, as a primary data validation tool for the Terra based MOPITT instrument. MOPITT-A is designed to operate aboard a NASA ER-2 research aircraft and as such must be rugged and field serviceable while maintaining the same characteristics as the satellite instrument. The resulting instrument is a hybrid of flight space components with commercial devices. Calibration data generated by both instruments, at the U of T Instrument Calibration Facility (ICF) will play a key role in data validation.

The MOPITT Airborne Test Radiometer (MATR) uses gas filter correlation radiometry to measure tropospheric carbon monoxide (CO) with three optical channels or methane (CH₄) with one channel. MATR uses the same gas correlation techniques as does the MOPITT satellite instrument, namely length modulation and pressure modulation MATR data serves to test retrieval techniques for converting infrared radiometric data into atmospheric CO, or CH₄ amounts. MATR will also be applied to MOPITT data validation. This paper gives an overview of the MATR instrument design; it discusses the results of laboratory testing and calibration; and it presents results from recent flights.

MOPITT is a nadir-viewing gas correlation radiometer due to be launched aboard the EOS Terra platform. The feasibility of MOPITT data validation using ground-based sun-viewing spectrometers of moderate resolution is investigated. Several instruments with a spectral resolution of approximately 0.2 cm^-1 are now operating in Russia and in China for the monitoring of CO and CH₄. A spectrometer of this type has been tested and improved at the University of Toronto. It has also been compared with other spectroscopic instruments in field conditions. The results of these comparisons, and the prospects for further work are presented and discussed.

The validation of MOPITT measurements of atmospheric carbon monoxide (CO) and methane (CH₄) will require independent, simultaneous, co-located measurements from ground- and aeroplane-based instruments. Recently, a program of MOPITT validation measurements in Russia and Canada has been proposed. This program will use three (nearly) identical Russian-made medium-resolution grating spectrometers (known as Sarcophagus) capable of measuring the atmospheric column concentration of CO and CH₄. Two of these instruments are located in Russia, and one in Canada. The similarity of these instruments provides the opportunity of acquiring a highly correlated validation dataset from diverse locations around the globe. As part of this program, we are proposing to inter- calibrate these instruments using a set of standard gas cells. These cells will be regularly shipped between the instruments for calibration and inter-comparison purposes. These measurements will be made relative to measurements from a very high-resolution Difference Frequency Laser Spectrometer (DFLS) located at the University of Toronto. In this paper we present the results of a test of this inter-calibration experiment using a single CO gas cell and involving Sarcophagus, a high resolution Fourier Transform Spectrometer (FTS) and the University of Toronto DFLS.

High time-resolved measurements of ozone during high altitude flights can address many scientific question regarding stratospheric ozone depletion, exchange processes across the tropopause and potential vorticity barriers -- such as the polar vortices and the sub-tropical barrier -- and the microphysics of ozone in clouds. A Fast OZone ANalyzer (FOZAN) was developed and installed on board of M55-Gheophysica, a stratospheric platform able to reach an altitude of more than 20 Km. FOZAN is a joint Russian-Italian instrument and uses the chemiluminescent heterophase reaction between ozone in the airflow and a solid state sensor; the luminescence intensity is proportional to ozone concentration, and it is registered by a photomultiplier. The devices includes an automatic self- calibrator, as well as an optical modulator, pump, microprocessor unit, air valve, ozone generator, ozone destroyer, thermostabilizer. This instrument comprises an electronic unit to control the instrument performance and to process measurement data. To improve the instrument sensitivity and measurement precision, synchronous digital detection and signal averaging are performed. The instrument features also a built-in calibrated ozone generator. The instrument was tested during test flights in Italy and was operated successfully during flights over mid-latitudes and Arctic region. A tropical campaign in spring '99 over the InterTropical Convergence Zone (ITCZ) took place in the frame of the THESEO project. The paper presents the design of the instrument, the result of laboratory tests as well as preliminary results of scientific flights on board of M55- Geophysica aircraft.

It is well known that a globally accurate, non-biased, satellite-derived sea surface temperature (SST) database has important applications in quantitative studies of the earth's atmosphere-ocean system. Current satellite SST retrieval algorithms do not provide the instantaneous accuracy of 0.3 K necessary for useful calculations of surface flux in climate modeling. The present study demonstrates the potential for utilizing high spectral resolution infrared radiance data toward the objective of improving global satellite-derived SSTs. The NPOESS aircraft sounder testbed interferometer (NAST-I), a newly developed experimental Fourier transform spectrometer, is employed here. This instrument is flown experimentally from high-altitude aircraft and is capable of cross-track scanning similar to that found on polar orbiting satellites; this unique scanning feature allows the possibility of accurate SST imaging. NAST-I data collected during the Wallops 1998 field campaign are used in a generalized physical multiwindow retrieval method. The combined technology and algorithm is anticipated to allow clear-sky imaging of SST with accuracy limited primarily by the noise and calibration errors of the instruments.

Biomass burning events and their effects are investigated using measurements from the Advanced Very High Resolution Radiometer (AVHRR) over Africa in 1997 and South America in 1995. Fires are detected, and aerosol optical thicknesses of the smoke pixels identified from the AVHRR imagery are retrieved using a table look-up approach. The retrieved mean aerosol optical thickness ((tau) _0.64) ranges from 0.3 to 0.6 over Africa and from 1.2 to 1.5 over South America. The top-of-atmosphere (TOA) and surface shortwave aerosol radiative forcings (SWARF) are estimated. Using two different approaches, the mean TOA SWARFs are about -20 and -40 Wm^-2, respectively, over Africa and about -50 and -60 Wm^-2, respectively, over South America, indicating an aerosol cooling effect. Over four sites where (tau) _0.64 measurements are available, values of aerosol single scattering albedos ((omega) ₀) are retrieved and surface downward shortwave irradiances (DSWI) are estimated using a radiative transfer model. Comparison of calculated DSWIs with observed DSWIs shows that, for 9 out of 12 cases, the root-mean-square (RMS) differences are within 35 Wm^-2. The largest error is about 70 Wm^-2, which is mainly caused by the uncertainties of the retrieved (omega) ₀. This suggests that DSWI can be properly estimated from AVHRR measurements if aerosol optical thickness is available.

One of the essential difficulties of spectral researchers atmosphere on scattering from ground Solar light is the contradiction between necessity of work with the small angular aperture, its need for satisfactory work of spectral devices, and with necessity of its increase to ensure a sufficient energy level of radiation on an input of photoreceivers. One of the decisions of this problem is installation of the spectral device (for example, Fabry-Perot interferometer) before focusing lens. Unfortunately such decision is connected to technological difficulties of creation of spectral devices with the large linear aperture. In submitted work the given problem is solved with the help of installation before an entrance of the photoreceiver of a mask adjusting phase structure of incident radiation, to ensure inphase addition of under different incident waves on spectrometer. Accounts of structures of such masks for interference-polarization light filter, Fabry-Perot interferometer with flat mirrors and Fabry-Perot interferometer with connected by convex and concave mirrors are resulted. Technological ways of creation of such masks are considered.

Global Measurements of water vapor in the upper troposphere and lower stratosphere (UT/LS) are required to assess its influence on the radiation budget of the Earth and for its use as a suitable tracer for the study of troposphere-stratosphere exchange processes (STE). MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) is a Fourier transform spectrometer measuring limb emission spectra. The field of view of the satellite-borne MIPAS/Envisat is rather wide compared to horizontal and vertical structures in real water vapor distributions (e.g. hygropause). Our aim is to derive UT/LS water vapor profiles from MIPAS/Envisat data with optimized spatial resolution and accuracy. The retrieval errors and vertical resolution were assessed in an altitude- range 5 - 25 km with respect to a MIPAS standard observation scenario and the retrieval of the water vapor profile to be performed on the measurement grid. As target parameters we used water vapor and continuum in the first case and water vapor, temperature and continuum in the second scenario. Improvements by joint retrieval of water vapor and temperature are investigated, in particular for saturated H₂O- signatures originating from the troposphere. The vertical resolution was estimated by the use of so-called averaging kernels.

A UV/Vis spectrometer (named GASCOD) for Differentiated Optical Absorption Spectroscopy (DOAS) has been developed at ISAO Institute and deployed for ground based measurements of stratospheric trace gases for several years at mid-latitudes and the Antarctic region. An airborne version, called GASCOD/A has been installed on board a M55-Geophysica airplane, a stratospheric research platform, capable of flying at an altitude of up to 20 Km. After a test campaign in Italy, the GASCOD/A performed successfully during the Airborne Polar Experiment in the winter 95/96. More recently, the instrument was upgraded to achieve higher sensitivity and reliability. Two additional radiometric channels were added. The input optics can turn in order to collect solar radiation from five different channels: one for detection of the zenith scattered radiation through the roof window (for DOAS measurement), two for direct and diffused radiation through two lateral windows and two for radiometric measurements through two 2(pi) optical heads mounted on the upper and bottom part of the aircraft and linked to the instrument by means of optical guides. The radiometric channels give us the possibility of calculating the photodissociation rate coefficients (J-values) of photochemical reactions involving ozone and nitrogen dioxides. The mechanical and optical layout of the instrument are presented and discussed, as well as laboratory tests and preliminary results obtained during flights onboard the M55- Geophysica.

This paper will describe the miniaturization of the Thermal Emission Spectrometer (TES) electronic system for use in the Miniature-TES (Mini-TES) being built for Arizona State University. Mini-TES will be used to measure thermal emission for mapping of surface minerals on Mars. Mini-TES is a single pixel, Fourier Transform Spectrometer, covering 5 - 28 micrometer at 10 cm^-1 resolution. The Mini-TES electronics incorporate modern Field Programmable Gate Array (FPGA) technology, surface mount designs, and simplified command, control and data protocol allowing for a 4 fold reduction in the electronics subsystem. Use of the Lander computer for shared signal processing further help to reduce the Mini-TES complexity. Details of the specific flight hardware design, actual hardware fabrication and initial test results will be discussed.