The availability of high performance two-dimensional InSb detectors enables the design and construction of mid-infrared spectrographs capable of obtaining high resolution spectra over extended spectral regions without moving components. Rugged, stable, cryo-cooled spectrographs suitable for remote field operation are now possible using prism-echelle cross dispersion designs. We discuss the design, fabrication, and performance of a high resolution mid-IR field spectrograph designed specifically for the detection of atmospheric-borne chemicals from airborne platforms. The instrument design provides maximum optical throughput covering the two atmospheric windows at 2.0 - 2.5 micrometers and 3.0 - 4.2 micrometers .

We have designed an immersion echelle-prism spectrograph for the remote detection of chemicals in the atmosphere. The instrument operates in the 2 and 3 micron atmospheric windows, and provides maximum throughput at 0.1 cm^-1 resolution. Crossed dispersers consisting of a high order silicon immersion echelle (13.5 grooves/mm) and 43 degree immersion prism (Rutherford prism) are combined in a Littrow configuration to generate a two-dimensional spectrum in the image plane.

Precise relative measurements of sky continuum and line emission and absorption have been made using FTIR spectroscopy. During conditions of horizontally uniform air composition, measurements of the variation of the spectral radiance with elevation angle sample an air column that varies simply as the cosecant of the elevation angle. In spectral regions that are optically thin, an extrapolation to zero air mass can be used to accurately determine instrumental background. An ambient temperature black body reference furnishes an accurate measurement of the instrumental spectral response. The excess sky emission above instrumental background relative to the local black body reference spectrum thus provides a calibrated sky radiance spectrum. This spectrum can be used to calculate the atmospheric transmission. As a test, transmission spectra have been directly obtained with the full moon as a backlighting source, and are in excellent agreement with the sky radiance derived transmission spectra. For spectral regions dominated by water, the continuum emission has been measured for paths involving the entire atmospheric column. Reasonable agreement with previous laboratory measurements of the continuum strength is obtained.

This paper focuses on a planetary Fourier spectrometer (PFS), an infrared device designed to be flown onboard the Russian-International Mission `Mars '94,' whose launch, planned for November 1994, has just been postponed to 1996. The design and production of the whole instrument results from international cooperation involving Russia, Poland, Germany, Spain, France and Italy; in particular, the University of Padova is responsible for the mechanical and thermal design of the interferometer, while the electronics are in the care of the CNR Institute of Interplanetary Space Physics in Frascati, Italy. This paper summarizes part of the work done at the University of Padova concerning thermal analysis and design; most of it was a preliminary study aimed at evaluating thermal disturbances and therefore the features of the thermal control system. Disturbances analyzed concern the long-wavelength LW channel operating in the range between 6 and 45 micrometers ; the effects of infrared emission of elements in the sensor field of view were evaluated and various solutions compared. With the implemented thermal control system the disturbance arising from the changes of sensor housing temperature is below 10% of the sensor electric noise while that resulting from structural parts in the sensor field of view is four orders of magnitude smaller. Temperature variations of the dichroic filter leads to errors comparable with sensor noise; the attempt of reducing the effect by stabilizing its holding structure proved ineffective, therefore calibration cycle must be more frequently performed.

Remote sensing of major and minor constituents in the earth's atmosphere is of great importance to the study of climate and global change. Because much of remote sensing involves placing instrumentation in environments that are not easily accessible, such as balloons, spacecraft, or remote field stations, it is usually necessary that the instrumentation be compact, lightweight, and rugged. This paper describes the development of a new type of remote sensing instrument we have chosen to call the multiplex Fabry-Perot interferometer (MFPI). We present atmospheric spectra obtained with our working prototype instrument. The MFPI is a Fabry-Perot interferometer for which the etalon plate separation is changed over a large optical distance during a measurement. When the resulting interferogram is Fourier transformed the multiple reflections within the etalon cavity produce a spectrum analogous to that which would be produced by an array of Michelson interferometers. However, for high spectral resolution measurements the scan distance required by the MFPI is much less than for the comparable Michelson. The MFPI will be ideal for remote sensing applications where weight, size, and mechanical reliability are primary considerations.

Instruments with very high spectral resolution are needed to sound stratospheric temperatures from satellite. Maximizing the contributions of the stratosphere to the upwelling radiance measured by a particular channel can be achieved by using high spectral resolution channels positioned at strong carbon dioxide (CO₂) line centers. In this paper, the techniques of stratospheric temperature sounding from satellite are briefly reviewed. The feasibility of high resolution stratospheric temperature sounding with the multi-order etalon sounder (MOES), a high resolution Fabry-Perot array spectrometer, is discussed. Our simulation studies indicate that stratospheric temperatures can be derived with a root-mean-square (RMS) error of about 2 - 3 K with MOES. A scenario to add MOES to the next generation high resolution infrared sounder (HIRS/3) currently under development with minimal cost is suggested. With its compact size and ruggedness, MOES is an ideal candidate as the stratospheric temperature sounding unit for small environmental satellite platforms.

Monitoring of the global distribution of tropospheric ozone (O₃) is desirable for enhanced scientific understanding as well as to potentially lessen the ill-health impacts associated with exposure to elevated concentrations in the lower atmosphere. Such a capability can be achieved using a satellite-based device making high spectral resolution measurements with high signal-to-noise ratios; this would enable observation in the pressure-broadened wings of strong O₃ lines while minimizing the impact of undesirable signal contributions (i.e., from the terrestrial surface and interfering species). 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 conceptual instrument design to achieve the desired measurement is presented. It involves a double-etalon fixed-gap 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. A retrieval technique has been implemented and is demonstrated for a tropical atmosphere possessing enhanced tropospheric ozone amounts. An error analysis assessing the impact on retrieved O₃ amounts of the most significant uncertainties associated with this particular measurement has been performed for several different types of atmospheres. Results show the proposed instrumentation to enable a good measurement of absolute ozone amounts and an even better determination of relative changes.

A limb sounding cryogenic IR telescope named CRISTA (cryogenic infrared spectrometers and telescopes for the atmosphere) has been developed to study dynamic disturbances in the middle atmosphere with high spatial (horizontal and vertical) resolution. For this purpose, it measures mid and far IR emissions of several trace constituents at earth's limb using three independent telescopes with high off-axis rejection performance. Height profiles are derived from simultaneous scans of the three telescope LOS. The radiation received is spectrally analyzed by grating spectrometers followed by Si:Ga and Ge:Ga detectors. High sensitivity together with improved spatial resolution leads to a spacing of only 500 km to 600 km between two adjacent measurement points and thus to a far more detailed picture of the atmosphere compared to present day satellite experiments. CRISTA, integrated in the free-flyer ASTROSPAS, is launched in 1994 by the space shuttle for a short duration mission and will be part of ATLAS 3.

A polar observatory has been in operation at Eureka (89 degree(s) north magnetic latitude) since 1990, with two studies centering on the dynamics of polar arcs and F-layer patches. Instrumentation has included all-sky imagers and multichannel scanning photometers. A recent addition has been a turntable photometer mount which permits continuous scanning along the dawn-to-dusk meridian. This is optimum for high resolution studies of sun-aligned auroral arcs and other particle precipitation affects poleward of the auroral oval. F-layer patches (whose optical signature are typically 100 - 300 R enhancements in 630 nm emission and lesser 558 nm enhancements) are frequently seen drifting across the pole in an antisunward direction, often in sequences and sometimes recurring through much of the 24-hr period. The instrumentation and results from these studies obtained over the 1993-94 winter are discussed.

A novel all-sky Doppler interferometer (ASDI) has been used to measure Doppler shifts and widths of nightglow emission lines from the upper atmosphere, thereby permitting determination of the neutral wind and temperature fields over regions up to 2000 km in diameter. The ASDI instrument consists of efficient all-sky (160 degree(s) field-of-view) input optics, a 100 mm aperture Fabry-Perot interferometer and output optics which focus 5 orders of the interference ring pattern superposed on the sky image onto a 512 X 512 pixel, LN₂-cooled (-150 degree(s)C) CCD detector. Good quality CCD images of the midlatitude nightglow oxygen 630.0 nm red line (approximately equals 300 km altitude) and 557.7 nm green line (approximately equals 105 km altitude) and the OH 799.4 nm line (approximately equals 86 km altitude) are obtained in 5 - 15 min exposures. The image signal-to-noise ratio is sufficient for division of the 5 circular interference rings into 24 equal azimuthal sectors, so that Doppler shifts and widths for 120 distinct regions of the sky can be obtained from one exposure. Wind and temperature fields derived from the ASDI nightglow 630 nm measurements are compared for observations following the autumnal and the vernal equinoxes.

Airglow imaging instrumentation has been developed to provide quality imagery of airglow in the visible and near IR wavelengths. The lower thermosphere airglow layers emit between 85 and 102 km altitude. The layers are structured with nonuniformity in the horizontal dimension as a result of atmospheric gravity waves (AGWs) passing through the layer and disturbing the nominal recombination processes producing intensity and temperature modulations. Imagers have been developed to measure the AGW-produced airglow nonuniformities. The instrumentation combines large format, low noise CCDs with large aperture optics for improved S/N images. In particular, the large dynamic range of the detectors provides information from the low intensity zenith sky and the bright, van Rhijn enhanced horizon simultaneously in all-sky fields. The imagers have been used effectively to identify AGW structure from a number of ground based facilities as well as a recent NSF sponsored aircraft campaign. Imagery from the OH Meinel bands and OI 5577 angstrom are presented. Discussions are also presented regarding Na 5896 angstrom, and O₂ atmospheric (0,1) band at 8650 angstrom emissions.

This paper describes Fabry-Perot/CCD annular summing applied to airglow observations. Criteria are developed for determining the optimal rectangular format CCD chip configuration which minimizes dark and read noise. The relative savings in integration time of the imaging Fabry-Perot/CCD system over the pressure-scanned Fabry-Perot/PMT system is estimated for the optimal configuration through calculations of the signal to noise ratios for three extreme (but typical) cases of source and background intensity. The largest savings in integration time is estimated for the daysky thermospheric [O¹D] (6300 angstrom) case where the bright (approximately equals 5 X 10⁶R/A) Rayleigh-scattered background dominates the read noise. The long integration times required to obtain useful signal to noise ratios for the faint (approximately equals 10R) nightsky exospheric hydrogen Balmer-(alpha) (6563 angstrom) reduce the importance of the read noise term and yield large savings in integration time. The significance of the read noise term is greatly increased with the very short estimated integration times required for bright (approximately equals 200R) nightsky lines such as thermospheric [O¹D]. Alternate CCD formats and applications methods that reduce read noise and provide improved performance in the latter case are compared against the CCD annular summing technique.

An advanced Fabry-Perot interferometer with an innovative focal plane detection technique called the circle-to-line interferometer optical (CLIO) system and high quantum efficiency CCD has been developed and field tested. During the field test at Ann Arbor, Michigan, 9 interference orders were collected simultaneously for the OH(7,3) P₁(3). A signal-to-noise ratio (SNR) of 10 - 100 was achieved with 1-minute integration. Compared with conventional FPI, the CLIO-FPI is more sensitive and capable of collecting airglow data at much higher temporal resolution. The first operational CLIO-FPI is deployed at the Polar Cap Observatory (PCO) at Resolute, Northwest Territories, Canada (74 degree(s)54' N, 94 degree(s)54' W), in 1994. This new instrument is expected to enhance our ability to study the Earth's mesosphere and lower thermosphere.

The wavelength region surrounding 1.0 micrometers has traditionally been a difficult one to observe. GaAs and silicon both have very low quantum efficiency in the NIR, while some improvements can be made by pre-flashing and oxygen soaking a silicon CCD. Greater improvement can be realized by using a material other then silicon as a substrate. Recently, detector technology has improved to the point where NIR observations can be made almost routinely. Scientifically, the NIR region is ideal for the study of molecular line and band emission, as well as low energy atomic transitions. A collaboration between Boston University and the Aerospace Corporation has resulted in a germanium based detector used in conjunction with an infrared optimized Fabry-Perot spectrometer. Gold plated mirrors were installed and the appropriate transmissive optics are used in the Fabry-Perot to optimize the NIR transmission. The detector is a germanium PIN diode coated with a layer of silicon-nitride. Current produced by the detector is measured by using a capacitive trans-impedance amplifier (CITA). An A/D converter samples the amplified capacitor voltage and outputs a 12 bit word that is then passed on to the controlling computer system. The detector, amplifier, and associated electronics are mounted inside a standard IR dewar and operated at 77 degree(s)K. We have operated this detector and spectrometer system at Millstone Hill for about 6 months. Acceptable noise characteristics, a NEP of 10^-17 watts, and a QE of 90% at 1.2 micrometers , have been achieved with an amplifier gain of 200. The system is currently configured for observations of thermospheric helium, and has made the first measurement of the He 10,830 angstrom nightglow emission isolated from OH contamination. In an effort to both increase the sensitivity of our Fabry-Perot in the visible and to adapt it for planetary astronomy we have entered into a collaboration with CIDTEC. A charge injection detector or CID has some unique capabilities that distinguish it from a CCD and we are evaluating it as a detector for the Hadinger fringe pattern produced by a Fabry-Perot. The CID allows non- destructive readout and random access of individual pixels within the entire frame, this allows for both `electronic masking' of bright objects and allows each fringe to be observed without having to readout a large number of dark pixels.

Spectral line profiles from light, atomic gases in upper planetary atmospheres are commonly non-Maxwellian. The velocity distributions of these light gases are perturbed in complex ways by atmospheric escape processes, by the paucity of thermalizing collisions, and by infrequent but important collisions with hot ions in the plasmasphere. It has long been recognized that the velocity distributions can be used to unfold the physical processes leading to atmospheric escape and to the partitioning of neutral gas trajectory classifications (ballistic, escaping, or satellite). Unfortunately, isolation of the velocity distribution from the measured emission line profile is not a simple matter, especially when neither of the velocity distributions are non- Maxwellian and when the instrument function used to measure the profile is also a complex function. We have experimented with several techniques to accurately retrieve the velocity distribution of atomic hydrogen in the earth's exosphere from the hydrogen Balmer-alpha (H_(alpha )) emission line profile measured with a Fabry-Perot interferometer. Although the derived velocity distribution remains subject to contamination of the measured emission by extraterrestrial and terrestrial sources, the technique to decompose the actual emission function from the combined instrument function plus emission function is established in this work -- and is applicable to many other similar problems. In particular, two techniques are compared. First, a classical deconvolution technique is developed using objective, low-pass filtering. Second, a nonlinear deconvolution algorithm, commonly referred to as `CLEAN' by the radio astronomy community that developed it, is applied to the optical H_(alpha ) spectra. We find that this second technique is useful for an accurate isolation of the velocity distribution of atomic hydrogen in earth's exosphere, while the classical deconvolution is more useful for determining the full width at half maximum of the emission. The CLEAN technique does a superior job of isolating low signal-to-noise information in the emission profile wings, of particular interest for the derivation of the escaping atomic hydrogen population. It is particularly important that the CLEAN technique, when properly applied, is not susceptible to the addition of unrealistic information in the low signal-to-noise region of emission line extrema, whereas common deconvolution techniques are often quite suspect in these regions. Using this new technique and a new ability to ascribe hydrogen column abundance to H_(alpha ) brightness measurements, we are now poised to derive atomic hydrogen escape fluxes without dependence upon models of escape flux dynamics.

A high-quality, large numerical aperture Fresnel zone device is being developed to enhance the performance of a Fabry-Perot interferometer (FPI) system. As predicted by the theory, the contributions from the successive interference fringes transmitted by this multiple Fresnel aperture increase the throughput of the FPI system many fold. This versatile optical element can also function as a lens, an aperture, and a filter resulting in a very compact system. For a given FPI resolution, a dramatic increase in the throughput and significant reduction in the instrument size attained by this experimental approach offers broad possibilities for major scientific advances for faint radiation measurements in several areas including astronomy, remote sensing of the atmosphere, x-ray microscopy, plasma research, and neutron imaging.

Ground-based observations of terrestrial dayglow emissions requires the measurement of a small signal embedded in a large background. We report the development of an instrument to accomplish this. Under sky background dominated conditions, the signal to noise ratio achievable for the measurement of an airglow line feature with a filter photometer depends little on the filter bandwidth. Thus, apart from spectral purity considerations, the only value of using a smaller bandwidth is that it reduces the number of counts needed to obtain the same statistical S/N. Critical design aspects include the development of the detector techniques needed to count very large photon fluxes generated by the bright daytime sky, and to maintain very high relative stability between the sky background and the dayglow feature channels. High counting rates are achieved by operating in analog mode using high bulk resistivity, low noise silicon didoes in an electrometer integrator circuit. High stability is achieved by using high resistivity dual diodes on a single silicon wafer, and locating the electronics in the same controlled environment. We demonstrate the use of such a filter photometer by the measurement of the diurnal variation of the 630 nm (red line) dayglow emission.

In a companion paper (Swift and Torr), we demonstrate a capability to observe thermospheric dayglow emissions from the ground using a novel photometric approach. In this paper we incorporate the principles of the technique into the design of a spectrometric facility capable of measuring the dayglow spectrum over the wavelength range 300 to 880 m at < 0.5 nm resolution with photometric like sensitivity, namely 50 counts/R at 300 nm and approximately 200 counts/R at 600 nm. the design is an all refractive f/1.4 distortion correctable grating spectrograph capable of operating over a full diurnal cycle with high sensitivity. The field of view is 14 degree(s). The instrument has a dynamic range of 10⁸, no moving parts except shutters, and a noise equivalent detection threshold of approximately 15R in the daytime and 0.01 to 0.1 R at night. The design comprises four spectrometric modules which provide simultaneous measurements of emissions in the 300 - 900 nm range. A 1024 X 1024 CCD is used for the detector. The facility should provide simultaneous measurements from the ground of the rich spectral content of the daytime mesosphere, thermosphere and ionosphere.

We describe a method for retrieving neutral thermospheric composition and solar EUV flux from optical measurements of the O⁺(²P) 732 nm and O(¹D) 630 nm airglow emissions. The parameters retrieved are the neutral temperature, the O, O₂ and N₂ density profiles, and a scaling factor for the solar EUV flux spectrum. The temperature, solar EUV flux scaling factor, and atomic oxygen density are first retrieved from the 732 nm emission, which are then used with the 630 nm emission to retrieve the O₂ and N₂ densities. Between the altitudes of 200 and 400 km the retrieval technique is able to statistically retrieve values to within 3.1% for thermospheric temperature, 3.3% for atomic oxygen, 2.3% for molecular oxygen, and 2.4% for molecular nitrogen. The solar EUV flux scaling factor has a retrieval error of 5.1%. We also present the results of retrievals using existing data taken from both groundbased and spacebased instruments. These include airglow data taken by the Visible Airglow Experiment on the Atmosphere Explorer spacecraft and the Imaging Spectrometric Observatory flown on the ATLAS 1 shuttle mission in 1992.

We report the design of a miniature imaging spectrometer array (ISA) for observations of the daytime and nighttime mesosphere, capable of operating in a spectral range extending from the near-ultraviolet (NUV) to the near-infrared (NIR) -- 260 to 870 nm. The instrument comprises an array of f/2 all-reflective imaging spectrometers with a 6 degree(s) field of view. The design comprises an offset single aspheric toroidal telescope mirror, a slit, an offset aspheric toroidal collimator, a plane reflective grating and a camera with three offset decentered aspheric mirrors. The optical system has a 75 mm effective focal length and approximately 7.5 micrometers spot size. The slit image curvature distortion for the system is less than 7.5 micrometers . Sampling of the image plane is provided by a 1317 X 1035 spatial x spectral pixel CCD array with 6.8 micrometers X 6.8 micrometers pixel size. Three modules of the array cover the wavelength range 260 to 400 and 550 to 870 nm at 0.3 nm spectral resolution. One high resolution module covers the range 306 to 310 at 0.05 nm resolution. This channel is used for the measurement of the hydroxyl radical. The sensitivity in the mid visible is approximately 0.1 counts/R-s/spatial bin, dropping to approximately 0.05 count/R-s/bin in the NUV. The readout electronics software allows the 1317 spatial pixels to be summed into any number of selectable bin sizes incurring a single read per bin. Since much of the full slit sensitivity is attributable to the large (6 degree(s)) field of view, the slit could be slanted with respect to the vertical, in order to enhance the sensitivity per vertical spatial bin, at the cost of some horizontal smearing. The instrument offers a powerful means for conducting comprehensive spectroscopic studies of the lower thermosphere and mesosphere, since the overall performance is better than that of the Imaging Spectrometric Observatory (ISO) flown on the ATLAS 1 shuttle mission in 1992. The weight and size reduction from the ISO to the ISA are approximately 270 kg to < 15 kg, and 20 cubic feet to 1 cubic foot respectively. The instrument has been designed specifically to address the issue of quantifying the chemical reactions which result in the natural destruction of ozone in the upper atmosphere. Expected measurements include the concentrations of O, OH, O₃ O₂, N₂, and the neutral temperature between 50 and 110 km. Concentrations H and HO₂ are indirectly determined from the data. The design meets NASA Administrator Daniel Goldin's challenge to build better, cheaper, smaller instruments for fast turn around small satellite missions.

A Loral 1024 X 1024 CCD array with 15-micron pixels has been incorporated as the focal plane detector in a new imaging spectrometer for auroral research. The large format low-noise CCD provides excellent dynamic range and signal to noise characteristics with image integration times on the order of 60 seconds using f/1.4 camera optics. Further signal enhancement is achieved through on-CCD pixel binning. In the nominal binned mode the instrument wavelength resolution varies from 15 to 30 angstrom across the 5000 to 8600 angstrom spectral range. Images are acquired and stored digitally on a Macintosh computer. This instrument was operated at a field site in Godhavn, Greenland during the past two winters (1993, 1994) to measure the altitude distribution of the various spectral emissions within auroral arcs. The height resolution on an auroral feature 300 km distant is approximately 1 km. Examples of these measurements are presented here in snapshot and summary image formats illustrating the wealth of quantitative information provided by this new imaging spectrometer.

The Arizona Airglow Experiment (GLO) is a panchromatic intensified CCD (ICCD) spectrograph, bore sighted with 12 monochromatic imagers. The spectrograph provides continuous spectral coverage from 1150 angstrom to 11,000 angstrom with a resolution of 5 angstrom to 20 angstrom. The spectrograph was designed to record simultaneously as much information as possible from a single column of gas. The resolution was selected to allow the determination of molecular emission vibrational and rotational structure. Molecular band emissions contain much more information than atomic lines, although interpretation of band emissions is more complicated. This complexity is due to the distribution of their energies over broad spectral ranges that overlap. The most productive method of interpreting molecular spectra is by modeling. The nature of the molecular transitions is well known, and synthetic spectra can be calculated to match the recorded spectrum accurately. Our knowledge of the transition probabilities allows accurate estimates of the intensity and shape of blended bands. It is our goal to synthesize all of the emissions recorded by the GLO as a tool to aid in detailed analysis of spectra. This work describes the approach used in calculating the synthetic spectra and references the source of parameters used for 14 band systems. This software utility will become a part of the GLO facility.

To study the polarization of sunlight scattered from polar mesospheric clouds (PMC) and the Rayleigh scattering from the upper atmosphere, we designed, constructed, and flew an ultraviolet imaging polarimeter (UVIP). A rocket-borne experiment, the UVIP consists of: an f/2 baffled telescope with a focal length of 76 mm; a filter/polarizer wheel with spectral bandpass and UV polarizing filters; a diode image intensifier; a thermoelectrically cooled, self-scanned diode array; and driver-interface electronics. The three polarization measurements are at 265 nm (8 nm spectral bandpass). Also, an unpolarized filter at 190 nm (20 nm bandpass) provides the color ratio 195 nm/265 nm. The Earth's limb is imaged onto the 128 pixels of the detector, observing tangent heights of 40 - 150 km with a height resolution of approximately equals 2 km. Previous optical measurements of PMC ice crystals indicate the particle scattering is Rayleigh-like, suggesting very high polarizations. To measure PMC against the ambient Rayleigh scatter requires 1% precision in polarization. Since we accurately know the polarization of the Rayleigh background, the technique is self-calibrating. We present the design of this instrument and example data from two rocket flights.

Limb observations of UV dayglow emissions from 80 to 300 km tangent heights were made in December 1992 using the GLO instrument, which flew on STS-53 as a Hitchhiker-G experiment. STS-53 was at 330 km altitude and had an orbit inclination of 57 degree(s). The orbit placed the shuttle near the terminator for the entire mission, resulting in a unique set of observations. The GLO instrument consisted of 12 imagers and 9 spectrographs on an Az/El gimbal system. The data was obtained over 6 days of the mission. Emissions from Mg⁺ and Ca⁺ were observed, as were emissions from the neutral metallic species Mg and Na. The ultimate source of the metals is ablation of meteors; however, the spatial distribution of the emissions is controlled by upper mesospheric and thermospheric winds and, in the case of the ions, by the electromagnetic fields of the ionosphere. The observed Mg⁺ emission was the brightest of the metal emissions, and was observed near the poles and around the geomagnetic equator near sunset. The polar emissions were short-lived and intense, indicative of auroral activity. The equatorial emissions were more continuous, with several luminous patches propagating poleward over the period of several orbits. The instrumentation is described, as are spatial and temporal variations of the metal emissions with emphasis on the metal ions. These observations are compared to previous observations of thermospheric metallic species.

The Upper Atmosphere Research Satellite (UARS) was launched in September 1991 with a complement of 10 instruments focused on the middle and upper atmospheric processes, and on solar irradiance variability. After nearly three years of successful UARS operations, eight of the ten instruments continue to operate. Data is routinely processed and reprocessed on a central facility. This data is now being distributed electronically to the scientific community. Among the more important UARS accomplishments are the first global mapping of ozone depleting chlorine radicals and reservoirs, measurement of middle atmosphere winds, the tracking of the Mt. Pinatubo aerosols, and highly accurate measurements of solar ultraviolet variability.

Measurements by the Halogen Occultation Experiment (HALOE), on board the Upper Atmosphere Research Satellite (UARS) are producing high quality atmospheric profiles of trace gases involved in ozone chemistry. Using eight IR channels to sense the atmospheric absorption of sunlight, HALOE is providing scientists with high quality global fields of HCl, HF, O₃, CH₄, NO, NO₂, H₂O, aerosol extinctions and temperature, shedding new light on the dynamics and chemistry of the atmosphere. Critical to the retrieval of atmospheric constituent profiles from space-borne spectroscopic sensors is the ability to determine the true path through the atmosphere of measured radiation. Since becoming operational in October 1991 new effort has been put into validating and refining the techniques required to estimate the tangent point altitude associated with each signal sample. This is accomplished by measuring transmission of sunlight in the CO₂ 2.8 micron region, and registering the CO₂ transmission profile with a modeled transmission profile based on temperature and pressure data from NMC or UKMO and an assumed CO₂ mixing ratio. In this paper we report on lessons learned during the data validation phase, and improvements made to the altitude registration process. The parameters and processes involved include CO₂ limb radiance inversion, signal processing, zenith angle estimation, refraction calculations, registration regions and aerosol effects. We also present the results of sensitivity and error analyses which reveal the accuracy required for each estimated parameter in order to register within the specified error budget.

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. Examination of various calibration data indicates the instrument has remained remarkably stable since launch. The instrument has a thermal drift of about 30 m/s/ degree(s)C (slightly dependent on wavelength) and a long-term temporal drift that has amounted to about 80 m/s since launch. These effects are removed in the data processing leaving an uncertainty in the instrument stability of approximately 2 m/s. The temperature control of the instrument has improved significantly since launch as a new method was implemented. The initial temperature control held the instrument temperature at about +/- 1 degree(s)C. The improved method, which holds constant the temperature of the optical bench instead of the radiator, keeps the instrument temperature at about 0.2 degree(s)C. The calibrations indicate very little change in the sensitivity of the instrument. The detector response has shown no degradation and the optics have not changed their transmittance.

Horizontal winds in the mesosphere and lower thermosphere are obtained with the high resolution Doppler imager (HRDI) on the Upper Atmosphere Research Satellite (UARS) by observing the Doppler shifts of emission lines in the O₂ atmospheric band. The validity of the measurements depends on an accurate knowledge of the positions on the detector of the observed lines in the absence of a wind induced Doppler shift. These positions have been determined to an accuracy of better than 5 ms^-1 from the comparison of winds measured by HRDI with those obtained by MF radars and rockets. In addition, the degrees of horizontal and vertical smoothing of the recovered wind profiles have been optimized by examining the effect both on the amplitude of the HRDI derived diurnal tidal amplitude and the variance of the wind differences with correlative data.

The wind imaging interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS) is a CCD imager which views a selection of airglow emissions at the limb through a field-widened Michelson interferometer. Winds are calculated from the Doppler shifts of the spectral lines, detected as changes in the phase of the fringes. WINDII has been operating in space for almost three years and its performance has been monitored over that time. It continues to function well, though subtle changes have been seen. This paper is a discussion of the endurance of the instrument and of the changes that have occurred during the mission.

Among the emissions viewed by the wind imaging interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS) are selected lines in the (0 - 0) transition of the O₂ atmospheric band. These lines are viewed simultaneously using a narrow band filter/wide- angle Michelson interferometer combination. The narrow band filter is used to separate the lines on the CCD (spectral-spatial scanning) and the Michelson used to modulate the emissions so that winds and rotational temperatures may be measured from the Doppler shifts and relative intensities of the lines. In this report this technique is outlined and the on-orbit behavior since launch summarized.

The Solar Stellar Irradiace Comparison Experiment (SOLSTICE) is a three channel grating spectrometer on the Upper Atmosphere Research Satellite (UARS). The instrument measures the solar irradiance in the ultraviolet, 120 to 420 nm, with a spectral resolution ranging from 0.1 to 0.2 nm. The prime science objective is to accurately measure the solar irradiance at wavelengths important to atmospheric photochemistry, with particular emphasis on determining the variation of the solar UV flux. In order to track changes in the instrument sensitivity, SOLSTICE has the unique capability of observing bright blue stars with the very same optics and detectors used for the solar observations. Individually, the ultraviolet flux from these stars should vary by only small fractions of a percent over time periods of thousands of years, but the average flux from the twenty calibration stars provides an even more stable reference. In this report we describe the instrument design and operation and illustrate the success of this technique during the first two years of the UARS mission.

The HIRDLS instrument is being designed to obtain data to address critical questions related to the middle atmosphere and its role in global change. We briefly state the scientific objectives of the experiment, and then describe the requirements placed on the instrument. These include the ability to obtain measurements with 4 degree(s)latitudinal and longitudinal resolution, and 1 km vertical resolution, the ability to sound down into the upper troposphere when clouds are absent, and the ability to measure radiance profiles in order to infer temperature and the concentrations of a number of trace species of different chemical lifetimes, along with the gradients of the geopotential height fields, for 5 or more years. The HIRDLS instrument is a multichannel infrared limb scanner that significantly extends the measurement capabilities of earlier instruments such as LIMS and ISAMS. Advances include the use of a two-axis scanner to allow limb scans at multiple azimuths, narrow fields of view coupled with over-sampling, digital filtering and low noise to enhance vertical resolution, the use of larger numbers of channels to acquire data over a larger range of altitudes and the use of a gyroscope to determine motions of the optical bench. The ways in which this is done are described. The most demanding requirements are for radiometric accuracy and precision, and for precise pointing knowledge (in the presence of vibration). The results of trade-off studies are presented, and the current conceptual design is described.

In this paper we describe the scientific design work behind the selection of the IR spectral passbands for the 21 sounding channels of the high resolution dynamics limb sounder (HIRDLS) which is scheduled to fly aboard the Earth Observing System (EOS) chemistry platform at the beginning of the next century. At least one radiometer channel must be used for each gas that is being measured. Preferably the interfering contributions to the radiance by other gases in a channel should be small, but the principle requirements are that the desired emission be measured with high signal-to-noise ratio, and that there be separate channels for the measurement of interfering species. However, more than one channel is required to provide full altitude coverage of those target gases such as CO₂, H₂O, and O₃, which have emission bands whose centers become optically thick in the middle atmosphere. Further channels, in which gaseous absorption is low, are required for the characterization of aerosol effects. We describe the HIRDLS channels selected for each gas, with emphasis on signal-to-noise considerations and altitude coverage, the elimination of contaminating signal between channels, and non-LTE processes for high altitude sounding and space view definition.

In order to measure the effect of rocket exhaust on stratospheric ozone and aerosol profiles, it is necessary to deploy a space-based mid-UV spectrograph capable of making measurements at high spatial resolution (1 - 2 km) of the intensity and state of polarization of solar light backscattered by the atmosphere. This paper describes the design of an instrument called HIROIG (high resolution ozone imager) which is expected to be deployed in a sun synchronous orbit sometime after 1995. The instrument consists of three identical spectrographs, each one sensitive to light polarized in one direction. Each spectrograph uses a frame-transfer CCD which images the entire 270 - 370 nm spectrum at approximately equals 1 nm spectral resolution. Images re exposed, in the push broom mode, for 140 msec, providing an effective spatial resolution of better than 2 km for typical orbital velocities. The HIROIG field of view is 1000 km cross-track. A ground-based prototype consisting of a single spectrograph has been constructed and the characterization of this instrument is discussed.

GOMOS is a medium resolution spectrometer designed to measure the concentrations of, and monitor the trends in, ozone and other atmospheric trace gases with very high accuracy. In addition, it can measure atmospheric turbulence, which is of interest for understanding the vertical exchange of energy between the lower and upper layers of the Earth's atmosphere. GOMOS offers global coverage in a broad spectral range, extending from ultraviolet to the near-infrared.

The polar ozone and aerosol measurement experiment (POAM II) was launched on the SPOT 3 satellite on 25 September 1993. POAM II is designed to measure the vertical profiles of the polar ozone, aerosols, water vapor, nitrogen dioxide, atmospheric density and temperature in the stratosphere and upper troposphere. It makes solar occultation measurements in nine channels defined by narrow-band filters. The field of view is 0.01 by 1.2 degrees, with an instantaneous vertical resolution of 0.6 km at the tangent point in the earth's atmosphere. The SPOT 3 satellite is in a 98.7-degree inclined sun-synchronous orbit at an altitude of 833 km. From the measured transmissions, it is possible to determine the density profiles of aerosols, O₃, H₂O, and NO₂. Using the assumption of uniformly mixed oxygen, we are also able to determine the temperature. We present details of the POAM II instrument design, including the optical configuration, electronics and measurement accuracy. We also present preliminary results from the occultation measurements made to date.

A conceptual space-based incoherent Doppler lidar wind measurement system is described. The system employs a Fabry-Perot interferometer to detect the Doppler shift of the backscattered laser line, and uses two channels, one for aerosol and one for molecular backscatter. Previous investigations have considered only the aerosol backscatter as the means to determine the Doppler shift. Several studies have demonstrated that aerosol backscatter, particularly over the oceans and in the southern hemisphere, can be extremely low in the free troposphere. The two channel configuration permits acceptable measurements regardless of the aerosol loading. The system operates in the near UV, which is eye safe and provides a large molecular backscatter. With a 20 Watt laser, 1 meter diameter collecting telescope, and 5 seconds integration time, the horizontal line of sight wind errors would be less than 1 m/s with aerosols typical of a continental loading from the surface to the stratosphere. Areas of low aerosol loading would have errors of about 3 m/s.

A number of interesting lightning events have been observed using the low light level TV camera of the space shuttle during nighttime observations of thunderstorms near the limb of the Earth. Some of the vertical type lightning events that have been observed will be presented. Using TV cameras for observing lightning near the Earth's limb allows one to determine the location of the lightning and other characteristics by using the star field data and the shuttle's orbital position to reconstruct the geometry of the scene being viewed by the shuttle's TV cameras which are located in the payload bay of the shuttle.

The sounding of the atmosphere using broadband emission radiometry (SABER) experiment has been selected for flight on the thermosphere-ionosphere, mesosphere, energetics, and dynamics (TIMED) mission expected to fly in the latter part of this decade. The primary science goal of SABER is to achieve fundamental and important advances in understanding of the energetics, chemistry, and dynamics, in the atmospheric region extending from 60 km to 180 km altitude, which has not been comprehensively observed on a global basis. This will be accomplished using the space flight proven experiment approach of broad spectral band limb emission radiometry. SABER will scan the horizon in 12 selected bands ranging from 1.27 micrometers to 17 micrometers wavelength. The observed vertical horizon emission profiles will be mathematically inverted in ground data processing to provide vertical profiles with 2 km vertical resolution, of temperature, O₃, H₂O, NO, NO₂, CO, and CO₂. SABER will also observe key emissions needed for energetics studies at 1.27 micrometers [O₂(¹(Delta) )], 2 micrometers [OH((upsilon) equals 7,8,9)], 1.6 micrometers [OH((upsilon) equals 3,4,5)], 4.3 micrometers [CO₂((nu) ₃)], 5.3 micrometers (NO), 9.6 micrometers (O₃), and 15 micrometers [CO₂((nu) ₂)]. These measurements will be used to infer atomic hydrogen and atomic oxygen, the latter inferred three different ways using only SABER observations. Measurements will be made both night and day over the latitude range from the southern to northern polar regions.

The temperature-ozone-nitric oxide experiment (TONE) on the thermosphere, ionosphere, mesosphere, energetics, and dynamics (TIMED) mission consists of two ultraviolet spectrometers and an infrared photometer. A medium resolution spectrometer (MRS) covers the spectral region from 210 to 247 nm with 0.2 nm resolution, and a low resolution spectrometer/infrared photometer (LRS/IRP) covers the 235 to 320 nm region with 2.0 nm resolution, and measures the 1.27 micron emission from molecular oxygen excited by ozone photolysis. The Earth's limb is scanned by articulation mirrors which also serve as the field- of-view limiting elements. The TONE measures profiles of emission as a function of altitude on the Earth's limb. The primary measurements include profiles of Rayleigh scattered sunlight and 1.27 micron emission in the mesosphere and lower thermosphere, and fluorescent emission from nitric oxide in the upper mesosphere and thermosphere. The inverted radiance measurements will yield profiles of temperature, density, and ozone in the mesosphere, and temperature and nitric oxide density in the thermosphere with 2.5 km vertical resolution and 4.5 degree spatial resolution along the orbital path. The primary TONE measurements extend from 50 to 180 km and are fundamental to the science objectives of the TIMED mission. The broad capabilities of the TONE contribute significantly to the TIMED mission with a low-cost, highly reliable instrument based on a long heritage of space instruments built at the University of Colorado's Laboratory for Atmospheric and Space Physics. The TONE has heritage from spectrometers on Mariner 9, Pioneer Venus, the Solar Mesosphere Explorer, Galileo, and Cassini.

The interpretation of infrared radiance measurements made by satellite-borne limb scanning broadband radiometers requires accurate and computationally fast techniques with which to evaluate the equation of radiative transfer. This requirement is made even more stringent when analyzing measurements of non-LTE emission from the terrestrial mesosphere and lower thermosphere. In principle, line-by-line calculations which explicitly account for the departure from thermodynamic equilibrium in both the source functions and the transmittances are necessary. In this paper we extend the emissivity growth approximation (EGA) technique developed for LTE conditions to the non-LTE environment. Computations of the non-LTE spectrally integrated limb radiance for the molecular oxygen airglow (1.27 micrometers and 762 nm), ozone and carbon dioxide in the 9 - 11 micrometers spectral interval, carbon monoxide (4.6 micrometers ), nitric oxide (5.3 micrometers ), and carbon dioxide (15 micrometers ) are presented. Using the non-LTE form of the EGA, the spectrally integrated limb emission is calculated for 35 tangent heights in the mesosphere and lower thermosphere (requiring a total of 1200 atmospheric layers) with line-by-line accuracy in only approximately 0.25 sec of CPU time on readily available desktop computer hardware, while the corresponding line-by-line calculations may require tens of minutes. The non-LTE EGA technique allows minor constituent retrieval algorithms to readily include non-LTE effects limited only by the a priori knowledge of the departure from LTE in the observed bands.

An imaging instrument is being developed for the NASA thermosphere ionosphere mesosphere energetics and dynamics (TIMED) mission. This instrument images the small, few km scale structure of the earth airglow. The measurement permits the remote sensing of the temperature and intensity fluctuations produced by atmospheric gravity waves propagating through the mesopause region. Instrument modules look in the nadir direction to observe the fine structure of the airglow. Other modules look at the limb in the satellite orbit plane to monitor the limb latitude profiles. The measurement is performed by observing the rotational temperature of the O₂(0,0) band at 762 nm in nadir and limb. The waves also modulate the airglow intensity and the instrument will record the modulations of the O₂(0,0), O₂(0,1) and OH emissions in the nadir. The nadir channels of the instrument use a wide angle telecentric imager in which the distortion of the image is closely controlled so that the motion of the satellite can be compensated during the extended integration time by time delayed integration (TDI) mode of scanning of the CCD. The TDI method requires the CCD pixel columns to be aligned parallel with the orbital velocity vector and the shifting of the rows to be synchronized with the satellite motion. Through TDI scanning the imager can stare at a target at atmospheric altitude for an extended exposure duration. Each telecentric instrument module contains a single filter, and adjacent wavelength bands are imaged simultaneously by passing the light through the filter at different angles. The limb imagers use CCDs in the frame transfer mode.

The global ultraviolet imager (GUVI) investigation is designed to provide quantitative observations and interpretation of the Earth's airglow and auroral emissions in support of the NASA thermosphere, ionosphere, mesosphere, energy and dynamics (TIMED) mission. It addresses TIMED objectives dealing with energetics, dynamics, and the specification of state variables. The instrument provides multiple-wavelength, simultaneous `monochromatic' images of the far-ultraviolet emission (115 to 180 nm) using a scan mirror to sweep the instantaneous field of view of a spectrographic imager through an arc of up to 140 degree(s) aligned perpendicular to the orbit plane of the spacecraft. The instantaneous field of view is 11.8 degree(s) by 0.37 degree(s) (adjustable) along the slit and perpendicular to the slit, respectively. The field of view is mapped to a two-dimensional image plane with up to 64 spatial pixels by 160 spectral pixels of spectral width 0.4 nm per pixel. Binning of pixels can be performed along both the spatial and spectral axes of the array to reduce the demands on the downlink telemetry. The f/3 Rowland circle scanning spectrographic imager is outfitted with a toroidal grating ruled at 1200 grooves per millimeter. The fore-optics consists of a plane scanning mirror and an off-axis parabolic telescope. The detector is a photon-counting microchannel plate with a wedge and strip anode mounted in a sealed tube.

The Solar EUV Experiment (SEE) selected for 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 above 25 nm and an avalanche photodiode for spectra below 25 nm. As part of the in-flight calibration plan, silicon XUV photodiodes with thin film filters are used as stable broadband photometers between 0.1 and 40 nm. In addition, redundant spectrograph and avalanche photodiode capabilities provide calibration checks on the time scale of a month, and annual rocket underflight measurements provide absolute calibration checks traceable to NIST photometric standards. All three types of instruments have been developed and flight proven as part of a NASA solar EUV irradiance rocket experiment.

Consider the evolution of a temporal signal X(t) that is an intrinsic random field. In the sense of a certain measurement-estimation experiment, the state of disorder of X(t) should increase toward an equilibrium state. The disorder of X(t) is measured by its `physical information' I, and the equilibrium state is determined by the condition that I be an extremum. The equilibrium state is shown to have a power spectrum S((omega) ) of the form (omega) ^-(alpha ), 1 <EQ (alpha) <EQ 2, that of 1/f noise.

This work is based on the use of diode lasers as spectroscopic sources for the observation and study of weak overtone bands of the NIR. The diode laser emission wavelength can be scanned around a gas resonance by sweeping its injection current, permitting a direct observation of an absorption line-shape. The resolution is limited principally by the effective laser linewidth, generally approximately equals 20 MHz in free running mode. The signal-to-noise ratio is increased by using the frequency modulation technique, and the excess laser amplitude 1/f noise is reduced by working at high frequencies. Since detectors operating at high frequencies are expensive and less sensitive, a good compromise is the two-tone frequency modulation technique, which uses two close high frequencies and collects the beat signal at lower frequency. Pressure broadening coefficients have been measured for some acetylene and ammonia absorption lines in the 790 nm bands and new lines have been observed. Pressure shift of two acetylene lines have been examined. It is shown that this spectroscopic apparatus can extract very weak signals from the background and can be a good choice when the space occupied by the spectrometer needs to be restricted into small volumes.

In Fourier transform spectroscopy degradation in spectral resolution and the introduction of false spectral features (`feet') both result from the limited optical pathlength used by a real instrument. This work describes a quantitative relationship between the truncation length of an interferogram and the distortion of the computed halfwidth for the three most common spectral shapes: Gaussian, Lorentzian, and Voigt profiles. The technique can also be used to aid in the alignment and calibration of a Fourier transform interferometer by deriving a calculated truncated interferogram lineshape of a `known' spectral line to compare with the lineshape actually produced by the instrument.

After point out the principles of the acousto-optic spectrometer (AOS) some questions about channels number and the AOS measurements uncertainties are discussed. To overcome the limits imposed by the acoustic attenuation and velocity one low cost LiNbO3 acousto-electro-optic interaction configuration with high channels number possibilities is proposed. Taking the turbulence and temperature effects on measurements uncertainties together it was established a criteria to use the spectroemter during for radio astronomy observations with lower uncertainties and costs.

Spatially resolved information from atmospheric-pressure helium inductively coupled plasmas (He ICP) was acquired with a simple, inexpensive optical imaging spectrometer. The system uses a 35-cm focal length Czerny-Turner monochromator/spectrograph and a solid state charge-injection device (CID) or a charge coupled device (CCD). Quantitative image maps of the plasmas were produced with good resolution. For example, when the CID was used, the entire plasma image could be monitored with a spatial resolution of 0.13 and 0.10 mm in the horizontal and vertical directions. The spectral resolution was 4 nm. Lateral distributions of emission intensities were converted, using an Abel inversion routine, to radial distributions. Some unique features of the He ICP, compared to the commonly used Ar ICP, were identified at or around analytical conditions for elemental analysis of gaseous and aqueous samples.

A joint radar/aircraft optical turbulence measurement is discussed. The joint measurement was made over White Sands, New Mexico with a KC135E aircraft equipped with fiber film temperature probes and a ground-based atmospheric profiler. General meteorological conditions were such that the turbulence on the day of the experiment was fairly weak. Emphasis was placed on the 36,000 ft to 42,000 ft altitude regime. Results showed good agreement between the atmospheric profiler and the aircraft-based measurements.

The Raman technique, while a valuable tool in chemical and combustion research, is limited in many remote sensing applications because of the low Raman scattering cross-section, which may be three to five orders of magnitude below the Rayleigh (elastic) values. Two concepts for increasing the signal level are discussed. First, use a range-gated Fourier transform spectrometer to increase the system throughput and allow multiplexing advantages. The spectrum is obtained by performing a FFT on the resulting interferogram. Second, since the cross section goes as the fourth power of the optical frequency, use ultra-violet laser illumination, and separate the resulting florescence radiation by placing a known dispersion on the transmitted waveform. The techniques for achieving this function, and the mathematical formulation for the phase-modulated auto-correlation which result, are not evaluated in this paper. However, the approach does not appreciably lower the available resolution because the limits are imposed by the sampling function inherent to the finite-duration Michelson mirror scan. A conceptual design using a long-pulse, flashlamp-pumped dye laser is shown, and typical performance equations in the detection of Freon 12, CCl₂F₂, are presented. For a one joule laser and a thirty (30) cm aperture operating in darkness, a concentration of 10²³ molecules/m³ can be detected in a 60 km visibility at a range of 3.4 km.

recent advances in silicon micromachining techniques allow the fabrication of very coarse infrared echelle gratings. When used in immersion mode the dispersion is increased proportionally to the refractive index. This permits a very significant reduction in the overall size of a spectrometer while maintaining the same resolution. We have fabricated a right triangular prism from silicon with a grating etched into the face of the hypotenuse. The grating covers an area of 32 mm by 64 mm and has a 97.5 micrometers periodicity with a blaze angle of 63.4 degree(s). The groove surfaces are very smooth with a roughness of a few nm. Random defects in the silicon are the dominant source of grating scatter. We measure a grating ghost intensity of 1.2%. The diffraction peak is quite narrow, slightly larger than the Airy disc diameter at F/12. However, due to wavefront aberrations, perhaps 15-20% of the diffracted power is in the peak with the rest distributed in a diameter roughly five times the airy disc.

The SWIF spectroradiometer was designed and built utilizing wedge interference filters (produced by Carl Zeiss of Jena, Germany) and a CCD-matrix (of Russian production) as sensors for use in ground-based and airborne optical sensing of the atmosphere and the surface in the spectral range of 0.35 - 1.15 micrometers . To perform absolute calibration of this instrument, a series of observations of direct solar radiation where made at Mauna Loa Observatory (MLO) in Hawaii in May - June 1993. The present paper is devoted to the description of the SWIF instrument and its absolute field calibration.

The use of limb radiation measurements to infer atmospheric parameters continues to be a popular technique. The HALOE (Halogen Occultation Experiment) instrument is a gas correlation radiometer on board the UARS (Upper Atmosphere Research Satellite) that performs solar occultation measurements for inferring vertical profiles of HF, HCl, CH₄, NO, O₃, H₂O, NO₂, aerosol extinction and temperature. The first four gases and aerosol are inferred from gas correlation measurements. The remainder are inferred from broadband (> 20 cm^-1) radiometer measurements. The eruption of Mt. Pinatubo before the UARS launch presented a number of challenges for HALOE data processing. Although ideally the gas correlation technique is insensitive to aerosol, in practice the aerosol signature induces optical effects that must be accurately addressed. The inference of extinction profiles for modeling aerosol signature in the radiometer channels was found to require high vertical resolution. The impact due to vertical resolution and other optical effects on the retrieved results is discussed. Simulations and HALOE results are presented to demonstrate and validate the effects. It is found that the Pinatubo layering demands a vertical resolution on the order of 2 km or less to accurately model aerosol effects on broadband limb viewing radiometers.

With the combination of a grism and a Kosters interference prism not only a beam doubling but also a reversion of the dispersion direction is achieved. With this principle a new type of an astronomical radial velocity spectrograph was designed. With this instrument radial velocities of stars in clusters, galactic field stars and of stars in the Magellanic clouds should be observable to a limit of about 15 mag with an accuracy of ±1 km/s with a im telescope. A description of the optical arrangement is given.

Accurate assessment of the potential impact of greenhouse gases and aerosols on the Earth system can be enhanced by a global monitoring network and can be facilitated by the development of compact, portable optical instruments for field use. The more important of these gases, e.g., methane (CH₄), carbon dioxide (CO₂), and nitrous oxide (N₂O), have strong absorptions at wavelengths between 2 and 5 micrometers ; however, this spectral region is heavily dominated by absorption by water (H₂O) which is itself an important contributor to radiative transfer at these wavelengths. To achieve the desired reduction in instrument size, it is often necessary to relax wavelength resolution requirements which in turn affects the accuracy and precision of the retrieved column abundances. To address these measurement problems, an infrared sun photometer has been constructed for application to trace-gas detection and analysis techniques are being developed to extract column abundances from the spectrally congested data. The current instrument design is based on a circular variable filter (CVF) with wavelength coverage from 1.2 to 5 micrometers . Preliminary measurements with this instrument are presented and electro-optical alternatives to the CVF as the tuning element are discussed.

The U.S. Air Force has long maintained an `exact' accelerated line-by-line (LBL) radiative transfer model, the Fast Atmospheric Signature CODE (FASCODE), appropriate for applications in both the laboratory and any arbitrary line-of-sight in the atmosphere. The first version was released in 1978 with optimized Voigt line shape decomposition and layering algorithms; it had a speed advantage of about 100 over existing fixed frequency LBL codes. The current version of FASCODE, FASCOD3, is fully compatible with the HITRAN92 database, including access to the temperature-dependent cross sections for heavy molecules (e.g., chloro-fluorocarbons/CFCs, etc.). Some new features of FASCOD3 are: line coupling algorithms for both 15 micron CO₂ and the mm lines of O₂; non-local thermodynamic equilibrium models; updated H₂O continuum; multiple scattering capability; and laser options for lidar modeling applications. Because of its speed over other LBL codes and extensive validations against measurements, FASCOD3 is increasingly being used as a high resolution remote sensing data analysis tool from microwave and infrared (IR) to ultraviolet (UV) spectral ranges.

A high spectral resolution lidar, under development by the Australian Antarctic Division and the University of Adelaide, is described. This instrument will be stationed at Davis, Antarctica (68.6 degree(s) S, 78.0 degree(s) E) from early 1996 for the long-term measurement of atmospheric parameters as a function of altitude from the lower stratosphere to the mesopause. The siting of the lidar will allow for data comparison with existing optical, radar, and balloon-borne atmospheric studies. Research utilizing the multi-instrument database will be aimed at assessing climatic variability and coupling processes throughout the atmosphere. The lidar transmitter consists of a commercial injection-seeded pulsed Nd:YAG laser coupled to a altazimuth mounted Cassegrain telescope with a 1 meter diameter primary mirror. The laser emits at a wavelength of 532 nm with an average power of 30 W. The telescope also serves as the collecting optics for the receiving system. The lidar is switched between transmit and receive modes by a high speed rotating shutter system. The detection system consists of a dual scanning Fabry Perot spectrometer (FPS) followed by a cooled photomultiplier operated in `photon counting' mode. The received signal is integrated as a function of equivalent range over a bandpass that may be either fixed or scanned in the wavelength domain. Performance simulations for the fixed bandpass operating mode are discussed. These indicate that useful measurements of density and inferred temperature should be achievable for the mesopause region, particularly at night and during twilight. In addition, detection of clouds in the mesosphere during the day appears feasible.

This review describes the step-by-step development and updating of the optical multipass system with a fixed path length and large relative aperture. Including some breaks in the work, the system has been improved for many years. The models were designed using the ratio between the base length of the multipass system and the focal length of an objective equal to 1.5, that ensured the development of a cycle of six-pass systems with a single objective. Of special interest is an original scheme with f number equals f/3.7 to be applied in high resolution spectroscopy. This brief review deals with various types of multipass systems developed for urgent high resolution spectroscopic applications in the Russian Academy of Sciences. Some of them have been widely acknowledged and independently applied in different fields of modern science and technology: i.e. laser techniques, metrology, spectral instrument engineering, and environment.