A priority in the Strategic Defense Initiative (SDI) is development of a space-based system to detect, identify, and track ICBMs. We show that ultraviolet surveillance provides advantages unavailable in any other wavelength band. During boost phase it should be possible to identify vehicles by their UV emissions and to track the hard body by detection of the vacuum core. After burn out, UV emission from shocked gas at the vehicle tip may be detectable. This is particularly important for surveillance of "fast burn" boosters, which burn out at a low altitude and hence are virtually invisible to infrared sensors by the time they reach an altitude where the atmosphere is transparent to IR radiation. We discuss the feasibility of tracking conventional and fast-burn vehicles via UV surveillance from space. Estimates of the UV brightness of typical targets are provided. We also consider the ambient day and night time background and evaluate the signal to noise ratio achievable under various viewing scenarios. We discuss instrumentation which should be capable of detecting and tracking such targets from geosynchronous orbit. An added advantage of UV surveillance is the availability of sensitive, rugged UV detectors which are under development by both the U.S. and the U.S.S.R.

Knowledge of the instantaneous state of the ionosphere can facilitate many components of C3I systems. Traditionally, ionospheric measurements have been performed using Langmuir probes, ion mass spectrometers, radars and ionosondes. The first two sample the ionosphere in situ, along the rocket or satellite trajectories. Besides being an active probing method, ground-based radio observa-tions are limited to a geographically fixed area surrounding the measurement site. In recent years it has been shown that ionospheric density distributions can be obtained by the remote sensing of selected Extreme Ultraviolet (EUV) emissions. The sensors for these measurements employ space-based passive detection techniques. The spectral region below 2000 A has successfully been used to both probe the upper atmosphere and image the aurora, even under fully sunlit conditions. The EUV measurements can also be used to infer the energy of precipitating electrons in aurorae. In this paper recent work in these areas will be reviewed. Requirements for future instrumentations will be discussed.

During the past ten years, the microchannel plate has become widely adopted as the preferred photon counting detector for low light level image systems at X-ray, extreme ultra-violet, and far ultraviolet wavelengths, especially in space astronomy applications. Various readout methods have been developed by workers in these areas, including phosphor/video, phosphor and binary-mask encoder, direct discrete position encoder, direct analog amplitude position-encoder systems, and delay line encoders. Salient advantages and limitations of these techniques are discussed in the context of low light level applications in space astronomy.

In recent years there has been considerable interest in the use of optically opaque layers of alkali halides on microchannel plates (MCP's) to improve quantum detection efficiency (QDE). However, only a few materials have been studied, in particular CsI and MgF2 in the soft X-ray regime (<200Å). We present comprehensive measurements of the quantum detec-tion efficiency for a number of materials, CsI, KBr, KC1, and MgF2, over a wide wavelength range (44Å to ~1800Å). These results show that high (>40%) quantum detection efficiency may be achieved for many materials, at certain wavelength regions in the extreme ultraviolet (EUV). We also observe structure in the wavelength dependence of the quantum detection efficiency that is directly related to the valence band to conduction band gap energy, and the onset of atomic-like resonant transitions. We show that a simple photocathode model allows interpretation of these features, and the variation of the quantum detection efficiency as a function of illumination angle. The structure of photocathode layers has been examined with an electron microscope, and shows that typical cathodes are granular. We also demonstrate that the cathode layer structure changes when degradation of the QDE occurs for hygroscopic materials.

Microchannel plates (MCPs) have been used as imaging photon counters successfully in the extreme and far ultraviolet (EUV and FUV) for many years. Charge Coupled Devices (CCDs), on the other hand, have become established for low light level sensing at visible and near infrared wavelengths (as well as X-ray). Recently, CCDs have been proposed as EUV and FUV detectors. With proper thinning and backside (input) surface treatments, the CCD quantum efficiency in the EUV and FUV is comparable and sometimes exceeds MCPs. A comparison of MCPs and CCDs for use in EUV and FUV low light level imaging is presented including: quantum efficiency, spatial resolution, format size, dynamic range and long term stability. The current best measured results for each detector type are reviewed as well as their own unique problems and limitations. The low light sensitivities in the ultraviolet achievable with optimized detector systems of each type are compared quantitatively for both for space-based astronomical and spectroscopic applications.

A 2D - photon counting imaging system, derived from the Mount Stromlo and Siding Spring Observatory concept, has been developed by MATRA for ground-based and spaceborne experiments. This system is described and its main performances discussed. The detector consists of a high gain image intensifier tube coupled to an array of 2D -CCD sensors by means of flexible optical fibre bundles (for image dissection). The dedicated electronic unit performs event detection and filtering, event centroid calculation and accumulation in a high speed incrementing memory. Some specific and critical techniques (direct optical coupling between fiber bundles and CCDs, realtime centroid calculation,...) and components (programmable array logic) are presented and discussed.

UV-photodiodes were fabricated by N-implantation in p-type 6H-SiC epitaxial layers grown on monocrystalline substrates. I-V characteristics (at 296-826 K) and spectral quantum efficiencies (at 295-673 K) are measured to characterize the photodiodes. Maximum quantum efficiences of 75% are observed at wavelengths around 280 nm. This means, that the diffusion length of the electron must be greater than 1 μm. From an analysis of the long wavelength cut-off, the band-gap energy and the temperature coefficient of the band-gap energy are determined.

The paper presents a newly developed helium-cooled spectrometer and radiometer with a diffraction limited telescope. The instrument is designed for ir-measurements aboard spacecraft. The instrument uses the the well-known limb technique to detect the spatially integrated spectral emission of the atmosphere and the atmospheric structure as well. The optical layout of the telescope is optimized for high straylight rejection of the earth s radiation and for good image quality. The telescope has an off-axis Herschel type arrangement. The focus of the primary mirror is reimaged with an elliptical (secondary) mirror into the instrument s focal plane. The suppression of the earth s straylight is achieved by means of an integrated Lyot optics, which are composed of field stop, secondary mirror and Lyot stop. This technique and high quality low BRDF mirrors give the off-axis rejection necessary for limb observations. The nominal focus of the telescope coinsides with the entrance slit of a spectrometer of Ebert-Fastie type. The detectors for the spectrometer cover the wavelenghts region between 2.5 μm to 25 μm in different grating orders, which are separated by means of wavelength selecting filters. The second focal plane instrument is a detector array specially designed for the scientific requirements. This array measures the ir-radiation in 10 spectral channels. The channel selection is performed with a filter wheel near the focus of the primary mirror. As the filters are not illuminated with parallel light the filter thickness and the cryogenic refractive indices of the filters have to be carefully taken into account.

The Improved Stratospheric and Mesospheric Sounder (ISAMS) is designed to measure the Earth's middle atmosphere in the range of 4.6 to 16.6 microns. This paper considers all the coated optical elements in two radiometric test channels. (Analysis of the spectral response will be presented as a separate paper at this symposium, see Sheppard et al). Comparisons between the computed spectral performance and measurements from actual coatings will be discussed: these will include substrate absorption simulations. The results of environmental testing (durability and stability) are included, together with details of coating deposition and monitoring conditions.

This paper provides the main outcomes from studies dedicated to the Infrared Sounder for Second Generation Meteosat. These studies are performed by Matra Space Branch and supported by European Space Agency (ESA) and Centre National d'Etudes Spatiales (CNES). Various instrument concepts are compared and two prefered options are more fully described, which apply respectively to 3-axis stabilized and spinning platforms. Possible improvements or simplifications of the baselines are identified.

Preliminary test results from the evaluation of Si:Sb and Si:Ga 58 x 62 element infrared detector arrays are presented. These devices are being characterized under background conditions and readout rates representative of operation in orbiting cryogenically-cooled infrared observatories. The arrays are hybridized to silicon direct readout multiplexers which allow random-access and non-destructive readout. Array performance optimization is being conducted with a flexible microcomputer-based drive and readout electronics system. Preliminary Si:Sb measurements indicate a sense node capacitance of 0.06 pF, peak (28 μm) responsivity >3 A/W at 2V bias, read noise of 130 rms e-, dark current ~10 e-/s, and a well capacity >105e-. The limited test data available on the performance of the Si:Ga array are also discussed.

A method to determine environmental noises between a radiometric sensor and a vegetation canopy is described. The noises are the differences between the incoming radiation and a synthetic radiation, computed by a radiation model in which the local climatological data are introduced over the evapotranspiration component. Climatological data are simultanously collected by sensors in the station and target area over a local area network (LAN), controlled by a master station in the radiometer standpoint. The LAN can quickly be rearranged in the observation area to get the actual amount of local environmental noises which then can be taken into consideration as corrections at the observed canopy reflectances. The method is primarily designed for remote sensing ground control.

The Astrometric Telescope Facility (ATF) is an optical telescope facility of extreme astrometric precision whose principal scientific purpose is the detection and study of planetary systems orbiting nearby stars. The ATF was planned as an initial operational capability (IOC) payload for the Space Station. A change in the Space Station program this year has resulted in a two-phase program. Phase I consists of the original Station's transverse boom with 75 kW of power initially, growing to 125 kW with addition of solar dynamic power, and Phase II adds the upper and lower booms. Only Phase I is currently approved and funded for development. If early operations are important for payloads such as ATF which were originally planned for the upper or lower booms, their suitability for the Phase I Space Station must be evaluated. This paper presents the results of such an evaluation for the ATF. The primary suitability considerations for an ATF Space Station mounting site are mechanical vibration, optical surface contamination (exhaust gases from station-keeping, gaseous and liquid dumping, pressurized module leakage, and particulates), and observable field of view. Specific quantitative environmental data for vibration, exhaust gases, and particulate contamination for the Station are incom-plete. Therefore, the results reported here are preliminary and based upon limited data and some modeled estimates. Only the field of view evaluation was straightforward and based on dimensions from the Space Station Phase B engineering study. Findings from this study show that the Phase I Space Station is marginally acceptable as an ATF platform. The Phase I Station provides an adequate field of view for observations, the vibrational environment is acceptable, and the contamination level during Station quiescent times (without venting) is acceptable. However, the contamination evaluation here is based on partial data and when the contamination levels are fully specified they are expected to exceed ATF's contamination requirements. Therefore, the acceptability of siting the ATF on the Phase I Station will depend upon engineering solutions being found to control the contamination environment. Thus, comparing the Phase I Station to the Phase II Station upper boom for siting ATF, the Phase I Station with higher levels of contamination and vibration levels, is a less desirable platform for ATF. The basic robust design for ATF with minimal design enhancements and with favorable control in the design of the Station, could make the Phase I Station acceptable for ATF operations.

The Vega 2 spacecraft of the Halley's exploration mission was equipped with a rotatable platform designed to accurately follow the cometary inner region during the observation sessions. Among the three optical instruments fixed on this platform was a multi-element spectrometer designed to obtain a detailed spectroscopic description of the inner part of the coma which could not be observed from a ground or satellite-based telescope due to the high optical thickness of the comet head. The instrument was composed of two parts. The first one was a Cassegrain telescope of focal length 350 mm which formed an image of the comet on the entrance slit of the spectrometer. Its hyperbolic secondary mirror could be sequentially rotated around two perpendicular axes to explore a 2°x1.5° field of view with a moderate spatial resolution. The second part was a static spectrometer with a concave holographic grating and an intensified linear photodiode array. The spectral response function presented a width at half maximum equal to 4.5 pixel widths when the entrance slit aperture was equal to 0.050 mm (2 pixel widths). The elementary exposure time was set equal to 400 ms. The video signal was digitized on 12 bits. Eight consecutive spectra were accumulated inside the RAM in order to transmit a complete spectrum every five seconds. During the cometary encounter sessions on March 8, 9, 10, 1986, about 3000 spectra were transmitted to the Earth. The following emissions could be identified: CO2+, OH, NH, CN, C3, OH, C2, NH2, H2O.+ Very close to the nucleus the ejection rate of water vapor was directly deduced from its absorption at 121.6 nm. After an interplanetary journey of 15 months the instrument worked satisfactorily and provided a large quantity of new data about Halley's comet

Progress in the development of solid-state self-scanned imaging arrays for NASA space science applications is reviewed and recent developments are highlighted.

Tunable solid-state laser technology is rapidly expanding coverage of the electro-magnetic spectrum between 0.20 and 14.0 μm, while dramatically increasing efficiency, lifetime and reliability. The status of several laser technologies will be presented which will be available in the decade of the 1990's to conduct scientific measurements of planetary atmospheres and features of planetary surfaces from orbiting spacecraft.

Semiconductor injection lasers are an important ingredient required for realizing advanced sensor systems for space missions. Their main roles are envisioned in pumping and injection locking of solid state lasers, and as direct sources in shorter range applications.

There now exist global environmental phenomena which can only be scientifically understood by the development of a multidisciplinary approach to the study of our planet as a system consisting of the oceans, land masses, atmosphere, and biosphere. These phenomena are associated with continual global changes in the Earth's environment such as increases in the carbon dioxide content, fluctuations in the ozone layer, and increases in the acid content of precipitation. The future negative ramifications of these phenomena on our planet have been well documented. The solution to the long term problems arising from these changes requires both a multidisciplinary as well as a multinational approach. Part of the approach is in situ and laboratory measurements and experiments with concomitant satellite-based global remote sensing. An Earth Observing System (Eos) is planned to address many of the remote sensing requirements from low Earth orbiting satellites (Reference 1). A new initiative called Mission to Planet Earth, together with Eos, will eventually lead to a comprehensive scientific understanding of the entire Earth System (Reference 2). The overall Mission to Planet Earth envisions a space global observational system that includes experiments and free-flying platforms in polar, low inclination, and geostationary orbits, designed to operate for decades, serviced either by astronauts or robotic systems.

VEGETATION is one payload on the earth-observation satellite SPOT 4, launch scheduled in 1992. It is developped, assembled and tested by AEROSPATIALE, under CNES contract. Its objectives are : - primarily : an operational world-scale survey of the evolution of VEGETATION (forecasting of agricultural yields and environmental studies); - secondarily : the observation of oceanic areas. Field of view is ± 50.5°C (2 000 km on ground), with observation frequency of less than 2 days at equator. The system, equipped with its own telemetry channels and on-board computer , will send coded data according 2 types of observation : . world wide observation : recording, then time-tagged transmission, with a nadir resolution of 1.165 km x 1.165 km or (in an exclusive sense) 4.66 km x 4.66 km (agglomeration of 16 pixels), . regional observation real-time transmission, with a nadir resolution of 1.165 km.

The ROSIS imaging spectrometer concept is based on all-reflective optics and matrix CCD detector arrays. The instrument concept was defined and detailed within a national study for chlorophyll measurements from space platforms, which was the design determining mission objective in terms of high spectral and radiometric and moderate spatial resolution. A great variety of further mission applications in the field of ocean, land and atmospheric remote sensing is foreseen. Meanwhile, a first airborne prototype version is under development for delivery in late 1988, funded commonly by DFVLR, GKSS and MBB, which will be used to verify the technical sensor concept of ROSIS and its full application spectrum. ROSIS is designed to cover a spectral range from 430 to 960 nm in resolution steps of 5 nm per channel; a set of up to 28 spectral channels can be read out simultaneously at full spatial resolution, the full spectrum at reduced resolution. The selection of channels can be pre-programmed per orbit or aircraft flight out of the available 106 channels. The radiometric resolution is defined as 0.05% of the apparent albedo. The total FOV covers ± 16° per optics module. In view of the ESA (and NASA) planning for Polar Platform Missions, ROSIS could represent a promising candidate of multi-purpose remote sensing instruments.