The Ultraviolet Coronagraph Spectrometer is one of the instruments on board the Solar and Heliospheric Observatory spacecraft, which was launched in December, 1995. The instrument is designed to make ultraviolet spectrometric measurements and visible polarimetric measurements of the extended solar corona. Prior to launch laboratory measurements were carried out to determine system level values for many of the key performance parameters. Further measurements on instrument performance have been carried out since launch. Presented are descriptions of measurement techniques and representative results.

The Solar Ultraviolet Spectral Irradiance Monitor on the Upper Atmospheric Research Satellite (UARS) carries four deuterium discharge lamps to assist in tracking inflight degradation of the instrument in the spectral range between 115 nm and 410 nm. The lamps have been in orbit since the launch of UARS on 12 September 1991. In this paper we discuss the performance of the two most-used lamps during the first four years of the UARS mission, and offer recommendations for improving the ability of the lamps to track inflight degradation in future space instruments.

The Solar Ultraviolet Spectral Irradiance Monitor on the Upper Atmospheric Research Satellite has been measuring the solar spectral irradiance between 115 nm and 410 nm since October 11, 1991. The original goal of the experiment was to maintain an absolute accuracy of 6 - 10% (a wavelength dependent, 2-sigma value) and a precision of 2% over a lifetime of the experiment, perhaps as long as an 11 year solar cycle. To do this, one must provide a time dependent accounting of the degradation of the optical elements' responsivity. The instrument was designed to maintain its calibration through the use of two identically-designed spectrometers, redundant optical elements, and four deuterium calibration lamps. Calibration measurements, which include solar as well as lamp spectral scans, are performed cyclically at intervals of approximately 1-month, 3-months, 6-months, and 12-months. We discuss the technique of determining the wavelength dependent degradation of the routinely used optical paths from the calibration measurements of sun and lamps. In so doing, we demonstrate the multiplicity of calibration data required to sequentially refine determination of the working channels' degradation. Estimated responsivity changes are also shown for the four years plus of instrument observations.

Three TOMS (Total Ozone Mapping Spectrometers) of a new design series are scheduled to be launched successively over the next several years. Changes have been made in the area of instrument calibration which should significantly improve the precision of TOMS ozone measurements over their predecessors. In the BUV method for determining ozone overburden, the precision of retrieved ozone amounts is directly related to knowledge of changes in diffuser reflectance. A three solar diffuser system employed on a previous TOMS proved capable of detecting a 0.25% (2 (sigma) ) ozone error over the three year mission. In addition to multiple diffusers, the new TOMS have on board a system for monitoring diffuser reflectance which alone should maintain instrument calibration with a precision at least double that of earlier TOMS. Improvements in prelaunch calibration techniques should result in closer inter- instrument agreement, an important consideration when measuring trends with multiple instruments. Unfortunately, the agreement between instruments is not likely to be better than about 1% ozone.

A new instrument has been developed to measure spacecraft attitude which utilizes ultraviolet radiation scattered in the Earth's limb. The sensor consists of a very stable UV bandpass filter with a center wavelength at 355 nm, imaging optics, and a linear diode array detector. The radiance of the limb at this wavelength is dominated by Rayleigh scattering and typically decreases by 15% per kilometer above 20 km. The theoretical resolution at the limb of this device is 0.39 km per pixel for a nominal orbital altitude of 306 km (approximately equals 0.012 degree(s)) and represents a significant improvement over typical infrared-based attitude sensors which have an accuracy of approximately equals 0.1 degree(s). This system was integrated with the Shuttle Solar Backscatter Ultraviolet experiment and flown on STS-72 in January of 1996. The calibration and optical characterization of the device will be presented. Results from the first flight of this instrument, showing an agreement with available shuttle pointing data of +/- 0.05 degree(s), will also be discussed.

In this paper the sun and moon spectra observed by GOME are examined in detail. For the moon observations this paper presents the first analysis of spectra and all factors that contribute to the measured signal are analyzed in detail. It is shown that the moon spectra, like the sun spectra, can be used for monitoring of the instrument performance. The geometrical moon albedo over the complete 240 - 800 nm wavelength range as measured by GOME is presented and discussed. The polarization properties of sunlight and moonlight measured by GOME are investigated.

This paper systematically discussed the three-wavelength dual differential absorption lidar (dual-DIAL) method for measuring the stratospheric and tropospheric ozone profiles in the presence of high loading or inhomogeneous aerosols along the measurement path. Results of theoretical analysis and comparisons with DIAL and aerosol correction method show that the three-wavelength dual-DIAL method not only can greatly reduce the effect of aerosols on tropospheric and stratospheric ozone measurements, but also can get more accurate ozone profiles than DIAL after aerosol correction. The system error of three-wavelength dual-DIAL due to aerosols is kept in a low level. As the system error in the three-wavelength dual-DIAL is almost insensitive to the spatial inhomogeneity of aerosol loading and aerosol optical properties, this method does not need to known the detailed information about the spatial distribution of aerosol loading and aerosol optical properties. In the regions contained high loading or inhomogeneous aerosols, accurate ozone profile can be obtained directly from the lidar return signals with three wavelengths dual-DIAL method. Experimental results indicate the three wavelengths dual- DIAL method is effective.

Changes were made to improve the wavelength and irradiance accuracy of the Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) before being flown on the third Atmospheric Laboratory for Applications and Science (ATLAS-3) Space Shuttle mission. As a result, the Naval Research Laboratory's SUSIM program produced an improved solar spectrum covering the range 110 - 420 nm at 0.15 nm resolution. This spectrum can replace the results of the SUSIM Spacelab-2 which have been used for atmospheric models and as an extraterrestrial solar irradiance and wavelength standard. The improvements in the instrument and its calibration will be presented with a detailed error analysis. Comparison of this data against the Spacelab-2 and other solar UV spectral irradiance data will be discussed.

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, planned for launch in 1997. 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. it will also be used to detect and characterize local perturbations of the ionosphere due to natural and artificial events. Atomic nitrogen in the upper atmosphere will be measured by nitric oxide nightglow emissions resulting from its combination with atomic oxygen. Observations of stellar occultations by Earth's atmosphere will be used to measure the neutral density distributions of N₂ and O₂. Other objectives are to map and monitor the ultraviolet background in near-Earth space due to ionospheric and airglow emissions and extraterrestrial sources, and to obtain all-sky surveys of celestial point and diffuse sources. GIMI consists of two wide-field imaging cameras sensitive in three far- and extreme-UV spectral ranges (75 - 110 nm, 131 - 160 nm, and 131 - 200 nm), selected for their utility in day and night ionospheric and neutral atmospheric remote sensing. The GIMI sensors are based on electron-bombarded CCD arrays, with opaque alkali halide photocathodes and Schmidt or all-reflective optical systems.

We discuss several new uses of backscatter ultraviolet (UV) measurements in atmospheric remote sensing. Radiances in the UV from 310 - 340 nm are primarily sensitive to total ozone and the effects of clouds and the Earth's surface. We have modeled UV radiances in this spectral range to an accuracy of approximately 0.5% with an efficient radiative transfer model. We have retrieved accurate values of total ozone using continuous spectral scan mode data from the Nimbus 7 Satellite Backscatter Ultraviolet (SBUV) spectrometer. Systematic effects resulting from calibration and algorithmic errors have been removed. The continuous scan mode total ozone measurements serve as independent validation of total ozone measurements and trends derived from TOMS and SBUV discrete mode, both of which have better temporal and spatial coverage than SBUV continuous scan mode but fewer channels. At wavelengths between 340 and 400 nm, radiances are sensitive to several properties of clouds and aerosols. We have used rotational-Raman scattering signatures near 360 nm and at the 394 nm calcium solar Fraunhofer line to determine effective UV cloud pressures with both TOMS and SBUV in continuous scan mode. At 280 nm, resonance scattering from magnesium ions has been detected. Spatial and temporal variations in magnesium ion column abundances, including increases with increased solar activity, have been derived from SBUV continuous scan measurements.

We describe imaging detectors (approximately equals 350 g, 0.7 W), using microchannel plates (MCPs), for the ultraviolet imaging spectrometers on Planetary missions to Saturn and other planets. These detectors image by locating and counting individual photons one at a time, accumulating and storing the image in an external digital memory. The 1024 columns (spaced 25 (mu) ) are coded by 10 bits and the 64 rows (spaced 100 (mu) ) are coded by 6 bits. The detector head consists of a header-MCP housing, a chevron microchannel plate with a gain near 3 X 10⁶, and a proximity focused anode called a code plate. The electronics consists of a low power high voltage power supply, a set of 16 hybrid low noise differential charge amps, 16 comparators, and 16 latches. A miniature digital buffer memory utilizes a field programmable gate array. We describe the theory and performance of the 2D CODACON.

Atmospheric mesoscale (100's of meters to a few kilometers) temperature structure and the structure associated with thin cirrus and aerosol layers in the upper stratosphere and lower mesosphere are difficult to measure by ground and satellite based techniques. We show in this paper that the altitude range between about 10 and 80 km is amenable to satellite sounding techniques in the UV-visible-near infrared bands (approximately 200 to 900 nm). The rapid change in optical depth vs. line-of-sight (LOS) end point along a downward-viewing LOS in the 200 - 350 nm spectral range allows separation of atmospheric regions according to the LOS optical weighting functions. The UV imager weighting functions (200 - 300 nm) in combination with the satellite- sensor zenith angle effect allows sounding in the approximately 40 to 80 km region, while the visible band imagery allows detection and separation of high altitude cloud structure leakage from the UV images of clear-air density structure. The instrument requirements necessary to detect such structure and to discriminate aerosol-induced Mie scatter from Rayleigh scatter components consists of UV to visible band spectral imagers having sufficient spatial, temporal and spectral resolutions. Only moderate spectral resolution imagery in the 200 to 900 nm region over a range of sensor line of sight nadir angles is required to detect clouds and infer cloud types. However, high signal to noise ratios and high spatial resolution are required to characterize the structure power spectral density of clouds and clear-air scatter components. Middle atmosphere structure sounding capability on the mesoscale level allows connection between turbulent-like small scale atmospheric phenomenology and larger scale cloud-related and weather- driven atmospheric variability. We demonstrate the stratosphere-mesosphere sounding concept by applying a low altitude mesoscale stochastic structure (LAMSS) model. This model was derived from the NSS (non-stationary stochastic structure) model which utilizes multi-dimensional Fourier- space descriptions of wavelike, turbulent-like, and deterministic, large scale structure to simulate the effects of atmospheric earthlimb structure. LAMSS specifically address tropospheric background clutter processes such as clear-air wind shears, turbulence, temperature inversions, and cirrus cloud structure. The empirical models are applied to synthesis of visible, UV, and IR clutter backgrounds as measured by passive spectral imaging sensors such as the UVISI (UV, Visible Imagers and Spectral Imagers) sensors on the Mid-course Space Experiment (MSX). This paper analyzes images from MSX-UVISI to obtain cloud and atmospheric density structure characteristics in the 200 - 230 nm UV and 300 - 900 nm visible bands. These data illustrates the feasibility of the UV structure sounding concept by comparison to the synthesized structured backgrounds.

The GLO experiment is an on-going shuttle-based spectrograph/imager project that has returned ultraviolet (100 - 400 nm) limb views. High spectral (0.35 nm FWHM) and temporal (4 s) resolution spectra include simultaneous altitude profiles (in the range of 80 - 400 km tangent height with 10 km resolution) of dayglow and nightglow features. Measured emissions include the NO gamma, N₂ Vegard-Kaplan and second positive, N₂⁺ first negative, and O₂ Herzberg I band systems and both atomic and cation lines of N, O, and Mg. This data represents a low solar activity benchmark for future observations. We report on the status of the GLO project, which included three space flights in 1995, and present spectral data on important ultraviolet band systems.

A series of three-second firings of Space Shuttle Orbiter's 870-lbf Primary Reaction Control System thruster motors were photographed from the crew cabin with an intensified video camera. The spectral imager sequentially recorded 4 ms exposures at 30 Hz in six 20 to 30 nm FWHM channels centered from 400 to 800 nm, chosen specifically to study bi- propellant (monomethyl hydrazine fuel/nitrogen dioxide oxidizer) thruster exhaust chemistry. The species producing the visible radiance were earlier identified as CN, CH, C₂, NO₂, and HNO; the electronic bands originating from the same excited states of CN (B-X) and CH (A-X) extend into the near UV. Images of the vacuum core viewing within a few degrees of perpendicular to the first several meters from the exit plane were analyzed to relate the spatial distribution of exhaust product species and afterburning chemistry to a flowfield-kinetics model. Profiles of radiance transverse to the exhaust symmetry-axis show substantial limb brightening in all six channels, indicating that the distribution of the radiating species corresponds to a `zone'-type model of liquid-fuel film-cooled engine performance. Profiles of band radiance along the axis indicate the production and quenching of excited species as the exhaust gas adiabatically expands and cools.

This paper reviews selected previously published papers that have appeared since the last UV SPIE conference in 1994. The papers data from late 1994, 1995, and early 1996. The intent is to cover UV remote sensing applications, measurements, and associated models that relate to the thermosphere, the ionosphere, the aurora, equatorial disturbance regions, and solar flux. These remote sensing techniques rely on airglow or auroral radiances and on accurate knowledge of the solar flux. As previously, the wavelength region is from the beginning of the ultraviolet at 400 nanometers to about 1 nm.

Numerous instruments for UV-visible optical measurements of terrestrial backgrounds have recently flown or are scheduled for launch in the near future. In order to maximize the scientific return from such flight opportunities, simulations of data acquired by imaging and spectrographic imaging instruments spanning wide wavelength ranges are required to support experiment planning and post-launch data analysis/fusion activities. We are currently developing comprehensive capabilities for modeling these types of remote sensing data suitable for a number of mission-support applications, with specific focus on data acquired by the UVISI instruments on the Midcourse Space Experiment satellite. These capabilities are described in this presentation. The core modeling capabilities reside in a suite of well-tested first principles and empirical modeling codes for atmospheric radiances arising from a variety of physical processes (e.g., photoelectron impact excitation, Rayleigh and aerosol scattering, solar resonance and resonant fluorescence scattering, chemistry). Image generation and LOS spectral radiance evaluation techniques permitting continual change in observer location and viewing geometry without incurring large computational burdens have been set up to ingest the radiance modeling results to create high fidelity synthetic satellite data. Illustrative examples are presented.

Computational Physics, Inc. (CPI) has been under contract to the Air Force Phillips Laboratory/Geophysics Directorate to re-engineer CPI dayglow and nightglow codes conforming to modern programming standards, followed by testing and validation of these codes. The software and associated input files comprise that portion of AURIC for the modeling of dayglow and nightglow from 100 to about 900 nm (MODTRAN comprises the other portion). This paper will describe the current capabilities of the dayglow portion of AURIC and present selected dayglow results. The dayglow portion models photoionization, photodissociation, photoelectric energy degradation, photoelectron impact excitation, chemistry, solar resonance and resonant fluorescence scattering, and multiple scattering of optically thick lines. Calculated observables are ion and neutral densities and radiances of atomic lines and molecular band systems. AURIC is currently being used to analyze satellite optical data, perform studies of production and loss processes, and support satellite experiments through data simulations.

Ultraviolet (UV) radiation is gaining widespread acceptance in industrial processes. Measurement of UV intensity and total energy falling on a work piece is a valuable aid to process control. This paper describes two UV measuring instruments and their characteristics. The instruments are designed for use in a production environment and commercial available.

UV Curing is highly adaptable to printing, coating, decorating and assembling of a great variety of products and materials owing to some of its key attributes, it is: a low temperature process, a high speed process, and a solventless process--cure is by polymerization rather than by evaporation. The latest developments in UV lamps for industrial processing are presented. Among these are: (1) the selection and control of the lamp emission spectra to match the optical properties of the film and its photoinitiator, (2) sustained high power lamp operation at 6 kilowatts, and (3) the use of absorptive dichroic reflectors to manage the relative components of UV and infrared energy in the highly focused radiation delivered to surfaces being processed.

Two interagency solar ultraviolet spectroradiometer intercomparisons (September 1994 and June 1995) have been conducted at Table Mountain outside Boulder, Colorado. A third intercomparison is planned for June 1996 at the same location. The intercomparisons were organized by the National Institute of Standards and Technology (NIST) at a field site supported by the National Oceanic and Atmospheric Administration and included participants representing North American agencies currently monitoring solar ultraviolet irradiance. Instruments were characterized at the intercomparisons for wavelength error, bandwidth, and stray- light rejection. All instruments were calibrated for spectral irradiance responsivity by NIST personnel with specially developed quartz-halogen field irradiance standards. Thus, comparisons of synchronized solar irradiance measurements allowed true comparisons between instruments, without the added complication of differences in irradiance scales of the participants. Estimates of differences in individual network propagation of irradiance scales were made separately. In addition, there were extensive concurrent ancillary measurements in an effort to compile a standard data set. We will discuss the results of these experiments and the overall agreement between the participants.

The National Institute of Standards and Technology in Gaithersburg, MD is upgrading the Synchrotron Ultraviolet Radiation Facility (SURF II) electron storage ring to serve as an absolute radiometric standard of unprecedented accuracy spanning the soft x-ray through infrared spectral regions. Major upgrades in the storage ring magnet system will substantially improve the uniformity of the magnetic field accelerating the stored electrons, and permit the new facility (SURF III) to operate at higher electron energies, extending the useful spectral range to at least 600 eV (about 2 nm). Parallel improvements in radiometric measurement of stored electron current will reduce the absolute spectral irradiance uncertainty in SURF III to about 0.5% or less from the infrared through far ultraviolet spectral range. A recently completed cryogenic electrical substitution radiometer will be used for high accuracy radiometry (0.1% order absolute uncertainty) exploiting SURF as a bright ultraviolet source. These developments will reduce the uncertainty in SURF-based ultraviolet radiometry by a factor of two to five, depending on wavelength and application. We will review the current states of ultraviolet radiometry at SURF II, discuss the SURF III storage ring upgrade, and outline the new radiometry programs planned for SURF III.

The High Resolution Fly's Eye (HiRes) cosmic ray detector at Dugway Utah, measures UV scintillation light from extensive air showers. The detection technique is calorimetric in that the amount of light produced is proportional to the energy of the primary particle. Primary particle energies range from 10¹⁷ to more than 10²⁰ electron volts. The detector can measure air showers more than 30 km away, a distance of several atmospheric extinction lengths. Variations in the atmosphere can cause significant variations in the amount of light reaching the detector. Atmospheric monitoring is extremely important. This paper discusses a method, under development, that uses the HiRes detector to measure light scattered from pulsed collimated xenon flashbulb sources (Flashers). Discussion includes a description of the light sources and a preliminary data analysis to extract a measurement of atmospheric extinction length and scale height.

In this paper we present recent developments made in recent years on the advancement of ultraviolet (UV) materials based on GaN and related materials for remote sensing applications. Most research on III-nitride materials has been focused on lasers and light emitting devices. However, GaN and related materials (wide band gap materials) offer the possibility of improved quantum efficiency, intrinsic solar blindness, and adjustable UV threshold wavelengths. The band edge absorption is one of the fundamental parameters that one has to address when a UV detector or sensor is fabricated from GaN thin films or other related materials. New results on the temperature dependence of the optical absorption near the band edge of GaN thin films grown by different techniques will be presented. The results indicate that the band gap energy and its behavior as a function of temperature is sample dependence. The sample dependency is explained in terms of the presence of defects, extended defects, and dislocations introduced during growth. Despite the presence of a high dislocation density in GaN thin films (in the order of 10⁹ cm^-3), free and bound exciton lines were observed.

Instrumentation has been developed for investigating the ultraviolet and visible radiations that are emitted above certain thunderstorms at times of lightning discharges. These radiations are commonly known as sprites and blue jets. The main objective of this effort is to measure the electron temperature of these emissions. The instrumentation consists of a UV/visible imager with appropriate narrow band filters. Two photometers, each with a specified filter, complement the imager.

The Special Sensor Ultraviolet Limb Imager (SSULI) program involves the development of a series of five ultraviolet limb imaging spectrographs by the Naval Research Laboratory for the Defense Meteorological Satellite Program. In addition, a duplicate sixth instrument, the Low Resolution Airglow/Aurora Spectrograph (LORAAS) will be flown aboard the Space Test Program ARGOS satellite in late 1997. These instruments will measure vertical intensity profiles of the Earth's airglow in the extreme and far ultraviolet (800 to 1700 angstroms) with 19 angstroms resolution. The instruments view the limb using a rotating mirror to scan the 0.1 degree(s) X 2.4 degree(s) field of view from 750 km to 50 km tangent altitude. SSULI measurements will be used to infer altitude profiles of ion, electron and neutral density. The first SSULI is scheduled to launch in 2000, and coverage from all the instruments will provide a continuous atmospheric data set spanning an entire solar cycle. The first four SSULI instruments are complete, and detailed optical calibrations have been performed. Assembly and calibration of the remaining SSULI instrument and LORAAS are underway, and preliminary results are available. Preliminary results of the first SSULI instrument were reported in 1994. This paper updates the calibration results of the first instrument and presents a summary of the results of the next three SSULI instruments. Comparison between instrument characteristics are also discussed, including variations in calibration techniques. A brief discussion on the periodic calibration verification of the SSULI instruments during storage and prior to launch is included.