We describe the Special Sensor Ultraviolet Spectrographic Imager (SSUSI). This instrument consists of a scanning imaging spectrograph (SIS) whose field-of-view is scanned from horizon to horizon and a nadir-looking photometer system (NPS). The SIS produces simultaneous multispectral images over the spectral range 1 150 to 1800A. The NPS consists of three photometers with filters designed to monitor the airglow at 4278A and 6300A and the terrestrial albedo near 6300A. SSUSI will fly on the DMSP Block 5D3 satellites S-16 thru S-19. The instruments will be calibrated at the Applied Physics Laboratory's Optical Calibration Facility.

The Atmospheric X-ray Imaging Spectrometer (PEM/AXIS) aboard NASA's Upper Atmosphere Research Satellite (UARS) provides continuous horizon to horizon images, both day and night, of the 3to 100-keY x-ray flux emitted from the top of the atmosphere. AXIS achieves a spatial resolution to better than 100 km using a 1—dimensional array of 16 passively cooled silicon detectors. The primary purpose of this instrument is to provide a global monitor of electron energy input to the upper atmosphere. The intensity and energy distribution of electrons precipitating into the atmosphere can be inferred from the x-ray bremsstrahlung spectra. The resulting images and spectra are also a rich source of information on the structure and dynamics of the magnetosphere. AXIS is part of the Particle Environment Monitor (PEM) investigation on UARS, launched 12 September 1991 into a 585km by 57° inclination orbit. We describe the design, development, and calibration of AXIS and provide an assessment of its excellent on-orbit performance. The unique capabilities of x-ray imaging spectrometers are demonstrated through an analysis of specific examples from October and November 1991 .Important new developments for follow-on instruments also will be described.

When the Cassini spacecraft arrives at Saturn early in the next century it will carry an UltraViolet Imaging Spectrograph (IJVIS) designed and built by the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado. Observations made with the UVIS will support a broad set of scientific investigations including spectroscopy, imaging, and occultations. The UVIS consists of three spectroscopic channels covering the wavelength ranges 55—i 15 nm, 1 15—190 nm, and 160— 320 nm. Each channel has an off-axis parabolic telescope followed by a toroidal grating spectrograph and an imaging microchannel plate-CODACON detector. Mirror coatings and detector photocathode materials optimize the sensitivity of each channel for its particular wavelength range. Spectrograph entrance slit mechanisms provide four independent spectral and spatial resolution modes for each of the three channels. A fourth optical train consisting of an off-axis parabolic telescope and solar blind photomultiplier tube with a CsI photocathode provides a high sensitivity photometer mode within the UVIS. The UVIS configuration was selected as a balanced solution to a large number of engineering and scientific constraints. We describe these constraints, the optical design, and the anticipated performance of the instrument.

Observations of bremsstrahlung X rays emitted by energetic electrons impacting the earth's atmosphere can be used for remotely sensing the morphology, intensity, and energy spectra of electron precipitation from the magnetosphere. The utility of the technique derives from the broad energy range of observable X rays (2 to greater than 100 keY), the simple emission process, the large x-ray mean free path in the atmosphere, and negligible background. Two auroral X-ray imagers, developed for future spaceflight, will be discussed. PIXIE (Polar Ionospheric X-ray Imaging Experiment) is scheduled for launch on the NASA International Solar-Terrestrial Physics/Global Geospace Science program POLAR satellite in May, 1994. The POLAR orbit, with an apogee and perigee of 9 and 1 .8 RE (earth radii), respectively, affords the opportunity to image the aurora from high altitude above the north pole continuously for several hours. MAXIE (Magnetospheric Atmospheric X-ray Imaging Experiment) is scheduled for launch aboard the NOAA-I satellite in late 1992. The 800-km polar orbit passes over both the northern and southern aurora! zones every 101 minutes. The presentation emphasizes the experimental approaches used to exploit these very different orbits for remote sensing of the earth's aurora! zones.

WINDII is an imaging, field widened Michelson interferometer built by Canada and France for ffight on NASA's Upper Atmosphere Research Satellite, which was launched September 12, 1991. Its primary purpose is to measure winds in the 80—300 km region of the atmosphere by observing airglow emissions. It has performed well to date. The design of the instrument is outlined in this paper.

The RAIDS experiment is an optical remote sensing platform consisting of eight sensors (spectrographs, spectrometers and photometers) covering the wavelength range 550 A to 8744 A. RAIDS employs a mechanical scan platform to view the Earth's limb and measure vertical profiles of atmospheric dayglow and nightglow from the mesosphere to the upper regions of the F region ionosphere (75 -750 km). RAIDS will be flown on the NOAA J weather satellite through the auspices of the Air Force Space Test Program (STP). The RAIDS wavelength and altitude coverage allows remote sensing of the major, and many minor constituents in the thermosphere and ionosphere. These measurements will be used as part of a proof-of-concept for remote sensing of ionospheric and neutral density profiles. The RAIDS database will be used to study composition, thermal structure and couplings between the mesosphere, thermosphere and ionosphere. RAIDS is a joint venture of the Naval Research Laboratory (NRL) and The Aerospace Corporation. This paper describes the subset of RAIDS instruments developed at NRL covering the far to near ultraviolet (1300 A - 4000 A). A companion paper describes the balance of the experiment complement.

The RAIDS experiment consists of eight instruments spanning the wavelength range from the extreme ultraviolet (55 nm) to the near infrared (800 nm) oriented to view the Earth's limb from the NOAA-J spacecraft to be launched into a circular orbit in 1993. Through measurements of the natural optical emissions and scattered sunlight origmating in the upper atmosphere including the mesosphere and thermosphere, state variables such as temperature, composition, density and ion concentration of this region will be inferred. This paper describes the subset of instruments fabricated or otherwise provided by the Space and Environment Technology Center (formerly Space Sciences Laboratory) at The Aerospace Corp. The companion to this paper describes the instruments from the Naval Research Laboratory. The Extreme Ultraviolet Spectrograph (EUVS), the three fixed filter photometers 0! (630), 0! (777), and Na (589), and the near infrared spectrometer (NIR) will be described. These are all mounted on a mechanical scan platform that scans the limb from approximately 75 to 750 km in the orbital plane of the satellite every 90 seconds.

The far ultraviolet (FUV) imager for the International Solar-Terrestrial Physics (ISTP) mission is designed to image four features of the aurora: 0 1 lines at 130.4 nm and 135.6 nm and the N2 Lyman-Birge-Hopfield (LBH) bands between 140 nm -160 nm (LBH long) and 160 nm 180 nm (LBH long). We report the design and fabrication of narrow-band and broadband filters for the ISTP FUV imager. Narrow-band filters designed and fabricated for the 0 I lines have a bandwidth of less than 5 nm and a peak transmittance of 22.3% and 29.6% at 130.4 nm and 135.6 nm, respectively. Broadband filters designed and fabricated for LBH bands have the transmittance greater than 40% for LBH short and close to 60% for LBH long. Blocking of outof-band wavelengths for all filters is better than 0.001% with the transmittance at 121.6 nm of less than 10-6%.

A compact solar spectrograph based on the Rowland grazing-incidence design has been developed that covers 200-3200 A and has no moving parts; it will record the entire spectrum within its range in a single exposure on the basis of pinhole optics. Three gratings are used and these are recorded on a single CCD focal plane detector. Methods used to minimize the effects of scattering include its suppression with coatings and optical components; a detector layout that subtracts scattered light effects, and a photocathode that discriminates against long wavelengths.

New developments in transmission grating and photodiode technology now make it possible to realize spectrometers in the extreme ultraviolet (EUV) spectral region (wavelengths less than 1000 A) which are expected to be virtually constant in their diffraction and detector properties. Time dependent effects associated with reflection gratings are eliminated through the use of free standing transmission gratings. These gratings together with recently developed and highly stable EUV photodiodes have been utilized to construct a highly stable normal incidence spectrophotometer to monitor the variability and absolute intensity of the solar 304 A line. Owing to its low weight and compactness, such a spectrometer will be a valuable tool for providing absolute solar irradiance throughout the EUV. This novel instrument will also be useful for cross-calibrating other EUV flight instruments and will be flown on a series of Hitchhiker Shuttle Flights and on SOHO. A preliminary version of this instrument has been fabricated and characterized, and the results are described.

We are currently developing an instrument free from optical components to measure the full-disk solar spectrum in the extreme ultraviolet regime covering wavelengths from 75-500 A. The instrument, which will be launched aboard a NASA Black Brant sounding rocket in September 1992, consists of a windowless noble gas ionization cell followed by a toroidal electrostatic analyzer to spatially disperse photoelectrons as a function of their energies. A microchannel plate based position sensitive detector will be used to detect individual electrons, indirectly returning the solar EUV spectrum.

A sounding-rocket experiment is being developed for the study of EUV spectral irradiance and its effects on the upper atmosphere, using three solar EUV instruments devised by the Laboratory for Atmospheric and Space Physics. These include a 25-cm Rowland circle EUV spectrograph, an array of Si X-UV photodiodes, and an X-UV imager with 20 arcsec resolution of the sun.

We have developed a prototype spectrometer for space applications which require long term absolute EUV photon flux measurements. In this recently developed spectrometer, the energy spectrum of the incoming photons is transformed directly into an electron energy spectrum by taking advantage of the photoelectric effect in one of several rare gases at low pressures. Using an electron energy spectrometer operating at a few eV, and followed by an electron multiplying detector, pulses due to individual electrons are counted. The overall efficiency of this process is essentially independent of gain drifts in the signal path, and the secular degradation of optical components which is often a problem in other techniques is avoided.

We are developing a compact, rugged, high-resolution remote sensing instrument with wide spectral scanning capabilities. This relatively new type of instrument, which we have chosen to call the Fourier-Transform Fabry-Perot Interferometer (FT-FPI), is accomplished by mechanically scanning the etalon plates of a Fabry-Perot interferometer (FPI) through a large optical distance while examining the concomitant signal with a Fourier-transform analysis technique similar to that employed by the Michelson interferometer. The FT-FPI will be used initially as a ground-based instrument to study near-infrared atmospheric absorption lines of trace gases using the techniques of solar absorption spectroscopy. Future plans include modifications to allow for measurements of trace gases in the stratosphere using spectral lines at terahertz frequencies.

Recent CCDs have been found to be suitable for performing aeronomical-quality observations of airglow emissions with Fabry-Perot interferometers; the fringe quality is satisfactory, and standard reduction techniques are able to extract high quality geophysical data from their observations. An account is given of the initial problems for which satisfactory solutions have been found, including sensor cooling.

An overview is presented of an observational campaign which will measure (1) the seasonal variations of the CO mixing ratio on the Martian polar cap due to accumulation and depletion of CO during the condensation and evaporation of CO2, as well as (2) the early spring ozone and water vapor of the Martian north polar cap, and (3) the presence of H2CO, H2O2, and SO2. The lines of these compounds will be measured by a combined 4-m telescope and Fourier-transform spectrometer 27097.

To take advantage of the large luminosity-resolution product of the Fabry-Perot interferometer used in tandem with modest aperture telescopes, a Fabry-Perot interferometer has been developed that is widely adaptable to a variety of extended source observations. The instrument is designed for adaptability across a range of optical and near infrared spectral lines from 550 nm to 1,100 nm, which are characterized by a wide range of velocity distributions of the emitting species. The system features twin etalon configuration to provide extended free spectral range and to enhance contrast when observations include bright reflected solar or twilight backgrounds. Although the optical path and all optical elements of the system are readily accessible, the instrument is ruggedized for transportability and extended remote field operation once optically configured. State-of-the-art, but proven detectors (GaAs photomultipliers, large charge coupled devices, and Ge-Nitride integrating detectors) are featured to optimize instrument sensitivity, and are modularly adaptable.

The Earth Radiation Budget Experiment (ERBE) radiometers were designed to make absolute measurements of the incoming solar, earth-reflected solar, and earth-emitted fluxes for investigations of the earth's climate system. Thermistor bolometers were the sensors used for the ERBE scanning radiometric package. Each thermistor bolometer package consisted of three narrow field of view broadband radiometric channels measuring shortwave, longwave, and total (0.2 micron to 50 microns) radiation. The in-flight calibration facilities include Mirror Attenuator Mosaics, shortwave internal calibration source, and internal blackbody sources to monitor the long-term responsivity of the radiometers. This paper describes the in-flight calibration facilities, the calibration data reduction techniques, and the results from the in-flight shortwave channel calibrations. The results indicate that the ERBE shortwave detectors were stable to within +/- 1 percent for up to five years of flight operation.

The Lightning Imaging Sensor (LIS) wide field-of-view solid-state camera can measure the global distribution of lightning from LEO, through the use of a narrowband interference filter to detect the neutral O band at 777.4 nm. Prelaunch testing and calibration of the LIS has required three separate laboratory systems; absolute radiometric calibration of the sensor will be furnished over the whole spectral range by a high resolution monochromator and motorized gimbals.

The Earth Radiation Budget Experiment (ERBE) active cavity radiometers are used to measure the incoming solar, reflected shortwave solar, and emitted longwave radiations from the Earth and atmosphere. The radiometers are located on the NASA's Earth Radiation Budget Satellite (ERBS) and the NOAA-9 and NOAA-10 spacecraft platforms. Two of the radiometers, one wide field of view (WFOV) and one medium field of view (MFOV), measure the total radiation in the spectral region of 0.2 to 50 microns and the other two radiometers (WFOV and MFOV) measure the shortwave radiation in the spectral region of 0.2 to 5.0 microns. For the in-flight calibrations, tungsten lamp and the sun are used as calibration sources for shortwave radiometers. Descriptions of the tungsten lamp and solar calibration procedures and mechanisms are presented. The tungsten lamp calibration measurements are compared with the measurements of solar calibration for ERBS and NOAA-9 instruments.

The gains of an isoplanatic patch, both in diameter and in area, are presently derived for a Multiconjugate Adaptive Optics system through comparison with a conventional system for height-dependent refractive index structure coefficient. By treating the atmosphere as an N-layer model and keeping the isoplanatic patch size invariable for all layers, the patch gain is obtained.

As part of an ongoing investigation of airglow emissions from space, we have developed an intensified CCD imaging spectrograph for a sounding rocket project called General Excitation Mechanisms In Nightglow (GEMINI). The instrument, known as Limb Imaging Spectrograph for Airglow (LISA) will be used to measure the limb profiles of some important nighttime airglow emission features. The GEMINI rocket is to be launched from White Sands Missile Range, New Mexico, in early 1993. The payload will be three-axis stabilized and absolute pointing will be derived from a star video camera. In this paper the imager design is discussed and we present the results of some laboratory tests performed using an artificial source of the oxygen nightglow emission.

We have constructed a high resolution imaging spectrograph for use as a payload in a sounding rocket experiment. The spectrograph employs a modified Ebert-Fastie design using a LiF predispersing prism and a replica of the E1 echelle grating developed for the Space Telescope Imaging Spectrograph. The spectrograph is used as a focal plane instrument of the Jupiter Telescope, a Cassegrain telescope constructed exclusively for use as a sounding rocket payload. The telescope and spectrograph were launched from the White Sands Missile Range on May 4, 1991 to observe the H Ly-alpha line profile spatially resolved across the disk of Jupiter in the north-south and east-west directions, and to measure the H Ly-alpha emission line profile from interplanetary hydrogen associated with the local interstellar medium.

We describe an instrument package to remotely measure thermospheric, exospheric, and plasmaspheric structure and composition. This instrument was flown aboard the second test flight of the Black Brant XII sounding rocket on December 5, 1989, which attained an apogee of 1460 km. The experiment package consisted of a spectrophotometer to measure He I 584 A, O II 834 A, O I 989 A, hydrogen Lyman beta (1025 A), hydrogen Lyman alpha (1216 A), and O I 1304 A transitions, and a photometer to measure the He II 304 A emission. The optical design of the spectrophotometer was identical to that of the Berkeley Extreme Ultraviolet (EUV) Airglow Rocket Spectrometer payload, flown on September 30, 1988 aboard the maiden flight of the Black Brant XII rocket. We present the initial data analysis and describe directions we will go toward the completion of our study.

The Ultraviolet Spectrograph Telescope for Astronomical Research (UVSTAR), is an EUV spectral imager for solar system and stellar astronomy that covers the 500-1250 A wavelength range with sufficient spectral resolution to distinguish atomic emission lines and form spectrally resolved images of extended plasma sources. UVSTAR employs a pair of telescopes and concave-grating spectrographs that cover the overlapping 500-900 A and 850-1250 A spectral ranges.

This paper describes a preliminary design for an imaging spectrograph that simultaneously covers the 2.15-5.2-micron spectral region with a resolution of 0.01 to 0.03 micron. Light entering the spectrograph through a slit is dispersed onto a 256 x 256 pixel InSb array by a novel spherical-faced prism/conic mirror combination. The use of a prism rather than a grating disperser allows more than a one-octave spectral interval to be covered with no moving parts. In addition, the prism optical efficiency remains high over the entire band covered. The simplicity and ruggedness of the design make it ideal for a space-borne instrument.

Ultrahigh resolution line studies can deepen insight into the excitation processes and structures of the upper atmosphere; attention is presently given to the possibility of a study of terrestrial atomic oxygen in the thermosphere through measurements of the O I 1304 A solar and terrestrial airglow emissions from a sounding rocket. These line profile studies of the airglow yield a relative contribution of the two main excitation mechanisms (photoelectron impact and solar-resonance scattering), as well as a verification of cross section and branching ratios.

Curtain shutter location has an effect on nodal camera performance; with large aperture and long focal length, the relative deviation of exposure is directly proportional to the distance between the shutter slit and the film. This will result in a degradation of imaging quality, an increase in distortion, and changes in the character of the exposure.

The Naval Research Laboratory is developing a limb imaging far- and extreme-ultraviolet (FUV/EUV) spectrograph (800-1700 A) to measure vertical profiles of the ionospheric and thermospheric airglow from DMSP Block 5D3 satellites. The spectrograph, called the Special Sensor Ultraviolet Limb Imager (SSULI), uses a near-Wadsworth optical configuration with a mechanical grid collimator, concave grating and linear array detector. Measured airglow profiles from the SSULI sensors will be used to infer vertical profiles of electron density and neutral density. At night, electron densities will be determined by measurement of ion recombination nightglow. Daytime electron densities will be obtained from measurements of multiple resonant scattering of O(+) 834 A radiation produced primarily by photoionization excitation. Dayside neutral densities and temperatures will be inferred from measurement of dayglow emissions from N2 and O produced by photoelectron impact excitation.

The Global Imaging Monitor of the Ionosphere (GIMI) is one of several remote-sensing instruments under development for flight on the Air Force Space Test Program's P91-1 Advanced Research and Global Observation Satellite (ARGOS), planned for launch in late 1995. The primary objective of GIMI is to map and monitor the ionospheric O(+) and electron density on a global basis, by means of wide-field imaging of ionospheric far-ultraviolet emissions. GIMI consists of two wide-field imaging cameras sensitive in two far- and extreme-UV spectral ranges (75-105 nm and 131-160 nm), selected for their utility in day and night ionospheric remote sensing. The GIMI sensors are based on electron-bombarded CCD arrays, with opaque alkali halide photocathodes and Schmidt or all-reflective optical systems.

Monochromatic imaging instrumentation has been developed that uses narrow-band (12 A FWHP) interference filters or plane reflection gratings for 2D imaging and imaging spectrograph applications. By changing the optics in front of the filter or grating, the field of view of the instruments can be varied from 180 deg to 6 deg. In the case of the 2D monochromatic imager, the 12 mm-diameter filtered image is formed at about f/1 on the input photocathode of an intensified CCD camera (380 x 488 pixels). The sensitivities of the systems are about 50-100 R s (S/N about 2). Examples of data taken with both of these instruments include detection and mapping of Jupiter's sodium magnetonebula and stable auroral red arcs in the terrestrial ionosphere.