The Earth Explorers are the research-oriented Earth observation missions of ESA. From a first set of nine proposed missions, four candidates have been selected for study at phase A level: gravity and ocean circulation mission, atmospheric dynamics mission, Earth radiation mission and land surface processes and interactions mission. Mission, system and instrument concept studies are in progress to prepare the phase A studies. First concepts for the complete system have been outlined for the complete system: spacecraft (bus and instrument) and its operation, ground segment and distribution of data. The four missions use different types of spacecraft: a dedicated satellite for gravity, the International Space Station as a carrier for atmospheric dynamics, a medium-size bus for radiation and an agile small satellite for land.

The Earth Explorers are the research-oriented Earth observation missions of ESA. From a first set of nine proposed missions, four candidates have been selected for study at phase A level: the gravity and ocean circulation mission, the atmospheric dynamics mission, the Earth radiation mission and the land processes and interactions mission. Mission, system and instrument concept studies are in progress to prepare the phase A studies and define the enabling technologies to be demonstrated to prove the feasibility of the candidates. The most critical technology requirements are specific to each mission and deal mainly with the gradiometer and the AOCS for the gravity mission, the laser and microwave transmitters for the atmospheric dynamics and the radiation mission and the infrared detectors and the AOCS for the land processes mission.

The Meteosat Second Generation (MSG) program consists of a series of 3 satellites, the objectives of which were defined by the European meteorological community led by the European Space Agency (ESA) and the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT). The development and procurement of the MSG satellite is under the responsibility of ESA. The corresponding ground segment will be procured by EUMETSAT, and they will operate the overall system. Aerospatiale of France leads an industrial consortium of more than 50 European companies that develop and manufacture the spacecraft. The objective of the MSG program is to provide a continuous and reliable collection of environmental data in support of weather forecasting and related services. A major element of this objective is fulfilled by the imaging mission, which corresponds to a continuous image taking of the Earth using 12 channels with a baseline repeat cycle of 15 minutes, including the on-board calibration and the retrace. The imaging tasks are performed by the spinning enhanced visible and infrared imager (SEVIRI), which is being developed by Matra-Marconi Space, France. Provision is also made for the satellite to carry as an experimental payload the so-called geostationary Earth radiation budget (GERB) instrument. This paper focuses on SEVIRI and its radiometric and imaging mission performances.

The microwave imaging radiometer with aperture synthesis (MIRAS) is an L-band two-dimensional interferometer which the European Space Agency is studying for the global mapping of soil moisture and ocean salinity. The antenna of this instrument has been optimized to reduce the number of receivers and correlators required for the interferometric processing. The antenna is an array of 3 coplanar arms spaced 120 degrees each one with 43 small antenna elements. In addition there is one element at the center of the array and, for calibration purposes, other three in between the arms. The in-phase and quadrature components of the voltage received by each small antenna in the array are correlated with those of any other antenna element. Every cross correlation is a sample of the so called visibility function at the spatial frequency defined by the relative coordinates of the corresponding pair of antenna elements. The brightness temperature distribution is then obtained basically by an inverse Fourier transform of the visibility function. Since more than one antenna pair may have the same baseline coordinates some spatial frequencies of the visibility function are measured more than once. These points of the visibility function are said to be redundant. This paper deals with the redundancy in MIRAS radiometer. The number of redundant points, its distribution in the spatial frequency domain and there the degree of redundancy is first analyzed. Then the correlation between redundant measurements is studied aiming at estimating the improvement in radiometric resolution when redundancies are combined. A trade-off between radiometric resolution gain and increased number of correlators is performed and some conclusions are finally drawn to be applied to the current design of MIRAS digital correlator unit. Passed preliminary results (Ref. 1) show that about 30% of all possible cross correlations correspond to redundancies while the estimated improvement in the radiometric resolution when using them is only of 1%.

In the last years aperture synthesis interferometric radiometers have received a special attention by space agencies as a feasible solution to passive monitoring of the Earth at low frequencies (L-band), where classical total power radiometers would require heavy steerable antennas to meet the spatial resolution requirements (10 - 20 Km), from a low polar orbit. While the performance of such instruments is well known in the radioastronomy field, its application to Earth remote sensing is quite new. The study of different array structures, system errors, calibration and inversion methods and instrument global performance requires the implementation of a simulator of a two-dimensional space borne interferometric radiometer. It allows us to analyze not only its snap shot radiometric accuracy, but also its improvement by means of pixel averaging, that is, the averaging of the common pixels recovered in a sequence of consecutive brightness temperature images. The simulations performed use the system parameters of the planned MIRAS (microwave imaging radiometer by aperture synthesis) instrument, a Y-shaped array with 43 antennas per arm spaced 0.89 lambda, currently under study by the European Space Agency.

An in-flight visible calibration system, VISCAL, is used to calibrate the visible/near infra-red channels of ATSR-2. The in-flight monitoring of the VISCAL is described and results presented. Data shows that the visible channels are affected by condensation effects as well as some long term degradation. The accuracy of the measured ground reflectances is dependent on the long term stability of the calibration. An area within the Libyan Desert has been used to determine calibration drift rates of 0.5% (1.6 micrometer), 1.8% (0.87 micrometer), 0.8% (0.66 micrometer) and 1.7% (0.56 micrometer) per year.

One of the key payload instruments of ESA's ENVISAT polar platform is the medium resolution imaging spectrometer (MERIS), aiming at improved knowledge of our planet in the fields of bio-optical oceanography, and atmospheric and land surface processes. MERIS, which is built under responsibility of Aerospatiale, will monitor the solar irradiation scattered by the Earth by employing five cameras which simultaneously record data in 15 visible and near-infrared programmable spectral bands with very low degree of polarization sensitivity. The combined field-of-view of the five cameras spans a range of 68.5 degrees. Crucial for obtaining the desired high accuracy during a four-years lifetime, is the on- board calibration unit. This calibration unit contains a set of Spectralon diffusers, which were manufactured having in mind excellent in-flight stability as well as spectral and spatial uniformity. Preflight calibration of the Spectralon diffusers was carried out at TNO-TPD. This calibration includes the measurement of the bidirectional reflectance distribution function (BRDF) for applicable angles and wavelengths, i.e., while varying angle of incidence, angle of observation, observation area on the elongated diffusers, wavelength and polarization. The diffuser calibration was performed in a class 100 cleanroom. For these measurements the TPD calibration facility, which is described in detail, has been adapted, so that it now has five geometrical degrees of freedom. Detectors have been optimized to minimize stray light. Due to extensive commissioning of the calibration setup the absolute error (1 sigma) of these measurements amounts to less than 0.5%; relative errors are in the 0.3 - 0.4% range.

ADEOS is the first polar orbit earth observation platform equipped with multiple earth observation sensors and it is no exaggeration to say that its scientific results will determine the future trends of global environment observation. It was launched from Tanegashima Space Center on 17 Aug. 1996, and all the eight sensors on-board had been operational and had sent data of the global environment. The contents of the ADEOS science program are preparation and adjustment of the program, development of algorithms, preparation of datasets, CAL/VAL of sensors and products, implementation of field campaigns, collection and analysis of field campaign data, management of JRA research activities, examination of ADEOS data system, arrangement of ADEOS sensor operation requests, and activities to disseminate and to encourage the use of ADEOS data. Unfortunately, ADEOs has stopped its operation on 30 June 1997 because of solar paddle failure. However, ADEOS had collected about 8 to 9 months data from its on-board sensors, and the ADEOS science program is still going on using these data. This paper describes the outline of ADEOS science program and its current status.

Initial on-orbit calibration results of the advanced visible and near infrared radiometer (AVNIR) onboard ADEOS were presented. When ADEOS returned over the Japan ground station mask on Sept. 1, 1996, AVNIR was first activated to evaluate performance. AVNIR calibration was then conducted using the reference signal sources (internal lamps, natural target data, NASA's airborne sensor data, etc.). The evaluation indicated that AVNIR has sufficient sensitivity to function as a high- resolution imager and is useful for the land monitoring, though some noises are to be removed.

Two methods for estimating overall system resolution characteristics of the AVNIR sensor system have been investigated: The frequency domain method (Fourier transform techniques) and the spatial domain method (spatial convolution techniques). Several factors affecting estimation accuracy of the spatial characteristics method were investigated using numerical simulations. Scene structures of a knife-edge target with step edges were used with a numerical estimation procedure to predict resolution performance in advanced Earth observing satellite (ADEOS) advanced visible and near-infrared radiometer (AVNIR) imagery. The results of both methods agree closely. An effective IFOV of about 20 meters was estimated from preliminary estimation experiments for AVNIR Mu bands.

The calibration results of the ocean color temperature scanner (OCTS) onboard the Japanese advanced Earth observing satellite (ADEOS) are presented in this paper. The goal of OCTS is to measure the geophysical quantities of the ocean (chlorophyll-a concentration, pigment concentration, etc.). They are calculated from the measured radiance by correcting molecular and aerosol scattering components, so the highly accurate calibration of the OCTS data is desired. For this purpose, OCTS is radiometrically calibrated using internal calibration sources (i.e., internal lamps, sun light, night times data, uniform target data), and external calibration source (NASA's airborne sensor underflights). It is also calibrated using the ground control points. As a result it was confirmed that OCTS data meets the specifications and provides accuracy for scientific use.

A satellite borne FTS called IMG (interferometric monitor for greenhouse gases) was developed by JAROS (Japan Resources Observation System Organization) deputed by MITI (Ministry of International Trade and Industry). It was installed on ADEOS (advanced Earth observing satellite) which was launched August 1996 by NASDA (National Space Development Agency of Japan). IMG is a very high spectral resolution (0.1 cm^-1) spectrometer that covers a wide range of infrared spectrum (3.3 - 14 micrometer). With these features, IMG could detect and monitor spatial and vertical distribution of greenhouse gases such as CO₂, CH₄, O₃, etc. over the entire Earth. Unfortunately, ADEOS stopped its operation on 30 June 1997, but about 8 months of data have been collected. IMG sensor characteristics and some of the initial scientific results are described.

POLDER is a CNES instrument on-board ADEOS polar orbiting satellite, which was successfully launched in August 1996. In November 1996, POLDER entered its nominal acquisition phase and functioned perfectly until ADEOS early end of service in June 1997. POLDER is a multispectral imaging radiometer/polarimeter designed to collect global and repetitive observations of the solar radiation reflected by the Earth/atmosphere system, with a wide field of view (2400 km) and a moderate geometric resolution (6 km). The instrument concept is based on telecentric optics, on a rotating wheel carrying 15 spectral filters and polarizers, and on a bidimensional CCD detector array. In addition to the classical measurement and mapping characteristics of a narrow-band imaging radiometer, POLDER has a unique ability to measure polarized reflectances using three polarizers (for three of its eight spectral bands, 443 to 910 nm), and to observe target reflectances from 13 different viewing directions during a single satellite pass. One of POLDER original features is that its in-flight radiometrical calibration does not rely on any on-board device. Many calibration methods using well-characterized calibration targets have been developed to achieve a very high calibration accuracy. This paper presents the various methods involved in the absolute in-flight calibration plan and the results obtained during the calibration phase of the instrument: absolute calibration over molecular scattering, inter-band calibration over sunglint and clouds, inter-calibration with OCTS, water vapor channels calibration over sunglint using meteorological analysis. A brief description of the algorithm and of the performances of each method is given.

POLDER is a CNES instrument on-board ADEOS polar orbiting satellite, which was successfully launched in August 1996. POLDER entered in its nominal acquisition phase in November 1996, and had been acquiring data till the loss of ADEOS in June 1997. POLDER spare model will be launched on-board ADEOS II in August 1999. This instrument is a multispectral imaging radiometer/polarimeter designed to collect global and repetitive observations of the solar radiation reflected by the Earth/atmosphere system, with a wide field of view (2400 km) and a moderate geometric resolution (6 km). Due to the wide field of view (around 50 degrees) and the important spectral range (from 443 nm to 910 nm), two different types of stray light phenomena have been identified during the radiometric on ground calibration. One is a local effect, that takes place around a light source, the second one is a global one, i.e. that a located light source creates stray light on the whole CCD detector. This paper first presents the analysis and characterization of these phenomena by means of instrumental measurements and a software simulation of the optics, then it describes the stray light calibration methods, and concludes with the correction method and its results.

The multiangular calibration is used to estimate the sensitivity changes in the different points of the wide field of view of an optical instrument equipped with linear or array detectors. The baseline method consists in having the instrument looking at a spatially uniform landscape. For a wide field of view instrument, continuous uniform landscape does not exist, so we propose a new method using several desert sites to simulate a spatially known landscape. Desert areas are already good candidates for the assessment of multitemporal calibration of optical satellite sensors. This requires that the sites be well characterized in terms of directional variations of their top of atmosphere reflectances, to account for variations in the solar or viewing configurations between each measurement. A ground campaign has been done to evaluate the bidirectional reflectances of different sites which are then used as reference. POLDER instrument is the first instrument using these references for the multiangular calibration. First, this paper describes the multiangular calibration method used on POLDER based on the knowledge of these desert sites. The site selection criteria and the method developed to localize these desert sites are remembered. Then the results are presented in different spectral bands and the performances of this calibration estimated.

EOS AM-1 is the first element of NASA's Earth observing system (EOS). EOS, the centerpiece to Mission to Planet Earth (MTPE), will provide long-term well-calibrated satellite observations to determine the extent, causes, and regional consequences of global climate change. EOS AM-1 will obtain information about the physical and radiative properties of clouds; air-land and air-sea exchanges of energy, carbon, and atmosphere; and volcanology. It carries five advanced instruments: advanced spaceborne thermal emission and reflection radiometer (ASTER) provided by the Ministry of International Trade and Industry of Japan, clouds and Earth's radiant energy system (CERES) provided by NASA's Langley Research Center, multi-angle imaging spectroradiometer (MISR) provided by the Jet Propulsion Laboratory, moderate resolution imaging spectroradiometer (MODIS) provided by NASA's Goddard Space Flight Center, and measurements of pollution in the troposphere (MOPITT) provided by the Canadian Space Agency. The project is currently in its D (development) phase and is scheduled for a June 1998 launch. All flight model instruments have been delivered and integrated with the spacecraft. The process of functional, compatibility, comprehensive performance, and environmental testing at the spacecraft-level is currently underway. During the next six months, this will be completed and the spacecraft will be prepared for shipment to the launch site. Results of these activities and the current development status are discussed. The EOS AM-1 project is managed by Goddard Space Flight Center.

Next June NASA will launch the EOS AM-1 mission, followed in July by the Landsat 7 mission. Since some of the scientific objectives require long-term observation, beyond the six-year lifetime of Landsat 7 and EOS AM-1, NASA has started initial planning of near-term EOS follow-on missions. To guide the planning of these missions, five science themes have been identified: land cover and land use change; seasonal to interannual climate prediction; natural hazards; long-term climate variability; and atmospheric ozone. Planning for near- term follow-on missions focuses on acquiring data within the land cover and land use change theme, providing broad continuity with EOS AM-1 and Landsat 7, but not mechanically replicating the measurements taken by those missions. Strawman measurements for the EOS follow-on missions include radiation budget; polarization; bi-directional reflectance distribution function; global land and atmosphere imaging; global ocean imaging; and high resolution imaging.

Landsat-7 will carry the enhanced thematic mapper plus (ETM+) as its payload. This instrument is a derivative of the thematic mapper (TM) instruments flown on the Landsat 4 and 5 spacecraft. Key changes to the instrument include a new 15 meter panchromatic band, an increased spatial resolution 60 meter thermal band and two new solar calibrators to improve the radiometric calibration of the reflective bands. The ETM+ is currently going through a series of radiometric performance tests to evaluate spectral responsivity, noise performance, linearity, radiometric stability, and absolute radiometric calibration in ambient and vacuum. To date, spectral responsivity, dynamic range, noise performance and absolute calibration tests have been conducted in ambient conditions for the reflective channels. System spectral responsivity, based on component level measurements, is similar to previous TM instruments. One notable difference is in band 5, where the ETM+ response cuts off near the nominal value of 1.75 micrometer versus the 1.78 micrometer of Landsat 4 and 5 TM's, providing a bandpass freer of atmospheric absorption. The gain setting on the reflective channels provided within-specification values of dynamic range and variations of less than 2% between detectors in a band for bands 1 - 5, and less than 4% for bands 7 and 8. Generally within-specification noise performance is observed on the instrument, with signal-to-noise ratios in the range of 150 - 300 at the upper end of the dynamic range. The current notable exception is the panchromatic band which shows significant coherent noise. In orbit, the ETM+ has three on board devices available for performing radiometric calibration: the internal calibrator (IC), the partial aperture solar calibrator (PASC) and the full aperture solar calibrator (FASC). The IC, which is similar to the internal calibrator on the thematic mappers, consists of two lamps, a blackbody and a shutter flag which transmits the light from the lamps and blackbody to the focal plane. The IC is calibrated prior to launch by reference to an external integrating sphere, using the ETM+ as a transfer instrument. The PASC provides a reduced aperture image of the sun on a daily basis. The FASC is a diffuser panel periodically deployed in front of the ETM+ aperture. BRDF measurements on a flight panel have recently been completed. The panel's reflectance varies little across the first four ETM+ bands, averaging about 0.91.

A benchtop virtual instrument simulator for CERES (clouds and the Earth's radiant energy system) has been built at NASA, Langley Research Center in Hampton, Virginia. The CERES instruments will fly on several earth orbiting platforms notably NASDA's tropical rainfall measurement mission (TRMM) and NASA's Earth observing system (EOS) satellites. CERES measures top of the atmosphere radiative fluxes using microprocessor controlled scanning radiometers. The CERES virtual instrument simulator consists of electronic circuitry identical to the flight unit's twin microprocessors and telemetry interface to the supporting spacecraft electronics and two personal computers (PC) connected to the I/O ports that control azimuth and elevation gimbals. Software consists of the unmodified TRW developed flight code and ground support software which serves as the instrument monitor and NASA/TRW developed engineering models of the scanners. The CERES instrument simulator will serve as a testbed for testing of custom instrument commands intended to solve in-flight anomalies of the instruments which could arise during the CERES mission. One of the supporting computers supports the telemetry display which monitors the simulator microprocessors during the development and testing of custom instrument commands. The CERES engineering development software models have been modified to provide a virtual instrument running on a second supporting computer linked in real time to the instrument flight microprocessor control ports. The CERES instrument simulator will be used to verify memory uploads by the CERES flight operations TEAM at NASA. Plots of the virtual scanner models match the actual instrument scan plots. A high speed logic analyzer has been used to track the performance of the flight microprocessor. The concept of using an identical but non-flight qualified microprocessor and electronics ensemble linked to a virtual instrument with identical system software affords a relatively inexpensive simulation system capable of high fidelity.

NASA's clouds and the Earth's radiant energy system (CERES) program is a key component of the Earth observing system (EOS). The CERES proto-flight model (PFM) instrument is to be launched on NASA's tropical rainfall measuring mission (TRMM) platform on 1 November 1997. Each CERES instrument contains three scanning thermistor bolometer radiometers to monitor the longwave and visible components of the Earth's radiative energy budget. An integral part of analyzing these measurements will be the use of high-resolution cloud imager data in conjunction with data from the CERES instruments. The use of high-resolution cloud imager data requires that the point spread function (PSF), or the dynamic response of the radiometric channels as they scan across a far-field point source, be well characterized. The PSF is determined by the field-of-view of the radiometric channel, its optical geometry, and the time response of the thermistor bolometer and its associated signal conditioning electronics. The PSF of the CERES instruments is measured in the laboratory using a state of the art radiometric calibration facility (RCF) developed by TRW. Intrinsic difficulties in making this measurement suggest that a better understanding of the data could be obtained by the use of an independent instrument model. High-level first-principle dynamic electrothermal models of the CERES radiometric channels have been completed under NASA sponsorship. These first-principle models consist of optical, thermal and electrical modules. Accurate optical characterization of the channels is assured by Monte-Carlo- based ray-traces in which tens of millions of rays are traced. Accurate thermal and electrical characterization is assured by transient finite-difference formulations involving thousands of nodes to describe thermal and electrical diffusion within the thermistor bolometer sensing elements and the instrument mechanical structure. The signal conditioning electronics are also included in the models. Numerical simulations of the PSF's of the CERES proto-flight model (PFM) radiometric channels have been completed. This paper presents a comparison between the measured PSF and the independent numerically predicted PSF for the CERES proto-flight model total channel. Agreement between the measured and predicted PSF's is excellent. The result of this agreement is a high confidence in the model to predict other aspects of instrument performance. For example, the model may now be used to predict channel PSF's for elevation scan rates different from the nominal Earth scan rate.

A series of observational performances tests and mechanical/thermal environmental tests had been performed on the advanced spaceborne thermal emission and reflection radiometer (ASTER) short wave infrared radiometer (SWIR) proto flight model (PFM). Radiometric resolution test results show that S/Ns (signal to noise ratio) are about 130 to 300 at high level radiance and about 35 to 70 at low level radiance for all six bands. Spectral characteristics test results show that center of band width, band width and band edge response are sufficiently good for the requirement to the ASTER SWIR PFM. MTF test results show values of about 0.4 at Nyquist frequency and 0.8 at 1/2 Nyquist frequency in square wave responses. Pointing performance test results show that good stability is accomplished with Stirling cycle cryocooler driving. The observational performances of the ASTER SWIR PFM do not show significant change throughout mechanical/thermal environmental tests. The environmental tests do not affect the alignment of the optical components.

The thermal infrared radiometer (TIR) is one of three radiometer on advanced spaceborne thermal emission and reflection radiometer (ASTER) which will be aboard NASA's EOS- AM1 polar orbiting platform to be launched in 1998. TIR will be used for precision observations in various fields, including solid earth science, resources exploration, cloud science, hydrology, and ocean science. Measurements by TIR will be made of surface temperature and emissivity, volcano activity, cloud top temperature, cloud structure, evapotranspiration, and ocean temperature. Manufacturing and testing of the proto-flight model (PFM) has already been done. This paper gives an overview of the proto-flight data based on the proto-flight test (PFT) for the TIR. Major performances are as follows: (1) modulation transfer function (MTF) is larger than 0.25 at Nyquist frequency. (2) Noise equivalent temperature difference (NETD or NE(Delta) T) is less than 0.3 K for 300 K target. (3) Dynamic range is between 200 K and 370 K. The standard blackbody with temperature between 100 K and 400 K was used in vacuum test for NETD, dynamic range and linearity. Also, the collimater was used for MTF and so on. Test has done well and results satisfied with all specifications.

The advanced spaceborne thermal emission and reflection radiometer (ASTER) is a facility instrument which has been selected by NASA to fly on the EOS-AM1 platform in 1998. Two independent cryocoolers are needed to cool down infrared detectors for the short-wave infrared radiometer (SWIR; 1.6 - 2.4 micrometer) and the thermal infrared radiometer (TIR; 8.3 - 11.3 micrometer). The goal in the development of the ASTER cryocooler is a durability of over 50,000 hours and mechanical vibration forces below 0.1 N in the frequency range from 40 Hz to 135 Hz in the directions of all three axes. A split- Stirling cycle cryocooler with clearance seals and linear electric motors is employed for this purpose. The compressor design for this adopts a piston driving mechanism which has a twin-opposed piston configuration, into one compression space. The mechanical vibration caused by an expander displacer is reduced by an active balancer. The cryocoolers for SWIR and TIR have a cooling capacity of 1.2 W at 70 K with power consumption lower than 55 W without control electronics. Two cryocoolers were evaluated from the viewpoint of cooling performance and mechanical vibration forces, and are presently undergoing life tests. The design concept and cryocooler performance test results which are indispensable for enduring a long life in space are described.

Advanced spaceborne thermal emission and reflection radiometer (ASTER) short wave infrared radiometer (SWIR) is planned to be launched with EOS-AM1 in 1998. SWIR has six bands and the linear detector arrays of all the bands are located on the same focal plane in parallel each other. Therefore parallax occurs between the six bands data. Large parallax causes errors in multiband data processing and so it is necessary to eliminate influential parallax from observation image. For the purpose of correcting parallax, we have developed a parallax estimation method for ASTER SWIR bands. To estimate parallax, image matching method is employed. But image matching method is not always effective. Cloud or featureless area in the image misleads the image matching process into a wrong result. So to prevent such misleading and to judge the validity of the result of the image matching method, coarse digital elevation model (DEM) data of which the cell size is about 1 km is introduced.

The ASTER (advanced spaceborne thermal emission radiometer) includes three telescopes sensitive to different wavelengths. As the telescopes are capable of changing sight directions, some band to band registration technique among images with different spectrum characteristics will be necessary. In this study, we propose a new registration method using image matching to deal with these problems and experimental results for airborne images are shown. This method is based on chip matching technique and consists of three processes. The experimental results were better than the results of the conventional method. The algorithm will be included to the ASTER level 1 data processing and the requirement that the band-to-band registration error should be less than 0.3 pixel will be achieved.

In order to simulate the ASTER's thermal infrared sensor that is one of the unique features of the ASTER, a new airborne thermal infrared imaging spectrometer -- airborne ASTER simulator (AAS) -- was planned and manufactured by a Japanese science group. The AAS having unique twenty bands in the TIR region was used for the field experiment in June 1996. Test site was Cuprite, Nevada, U.S.A. The basaltic zone, silicified mountain and playa are typical targets of the flights. The purpose of this experiment was to obtain the high spectral resolution TIR (thermal infrared) data. These data were used for the development and validation of temperature and emissivity separation algorithm. Along the trajectory on the ground, the radiance temperature measurement was synchronized with the AAS flight. ASTER simulation data sets were synthesized from these airborne data, and the performance of temperature and emissivity separation was evaluated by these data.

A sensitivity analysis of our own atmospheric code for a vicarious calibration of ADEOS/AVNIR was conducted. It was found that the most significant error source is the imaginary part of the complex refractive index of aerosol under the certain condition as well as a Mie phase function derived from the index through an inversion. A sensitivity of the phase function on the top of the atmosphere radiance was evaluated with our own atmospheric code including a radiative transfer code.

The presented technique of global operative ozone monitoring from high orbit satellites is based on the correlations of radiance field fluctuations observed in narrow spectral intervals of the ultraviolet (UV) spectral region with anomalies in atmospheric ozone distribution. This technique allows the real time control of the atmospheric ozone dynamics with high space and time resolution. The proposed experimental device includes the multichannel optical system based on the special narrow band UV interference filters with extremely low transmittance (less than 10^-3%) outside the band. The special method and an instrument to measure correctly such filter parameters as well as experimental results are also presented.

In-flight monitoring of the optical response of GOME revealed a number of instrumental features that drift or change with time. Some of these observed features are related to outgassing of the instrument in space. In particular outgassing of optical coatings, e.g. the dichroic mirror in GOME, can result in a change of the optical characteristics and thereby changing the response of the GOME instrument. Another feature is related to the etalon effect which results in a spectral modulation of the GOME spectra. This modulation varies in time due to a varying contamination layer, most likely ice, on the cooled detectors. Through the GOBELIN project the GOME breadboard model has been made available to us by ESA. The GOME breadboard model has been fully upgraded to represent the GOME flight mode and therefore offers a unique opportunity to study the above phenomenon under controlled laboratory conditions. First results are presented addressing in particular the effect of outgassing on instrument optical response, including the polarization response, and the etalon effect.

Satellites, and consequently satellite instruments, are undergoing size, power, volume and cost reductions, due primarily to national budget and commercial economic considerations. As instruments have become smaller, so have the filters used by them. Presently, several systems employ miniature multicolor focal plane filters, and more are planned. This paper documents the status of the development and refinements of these specialized devices in order to inform the instrument designer as to some of the newly available filter options, and hopefully to encourage new ideas for their use.

The paper introduces the concept that calibration/validation (cal/val) can play an essential role in bringing remote sensing to mainstream consumers in an information-based society, provided that cal/val is an integral part of a quality-assurance strategy. A market model for remote sensing is introduced and used to demonstrate that quality assurance is the key to bridging the gap between early adopters of technology and mainstream markets. The paper goes on to propose the semi-continuous monitoring of quality assurance and stability reference (QUASAR) sites as an important first step towards a cal/val infrastructure beneficial to mainstream users. Prospective QUASAR test sites are described.

In-flight calibration of space-based imaging radiometers is essential to allow corrections for changes in instrument response that occur during storage on ground, launch and operation in space. The most serious technical problems are in calibration for absolute spectral response in the waveband of reflected solar radiation -- visible through short-wave IR. Some concepts for in-flight calibration are presented, that are applicable mainly to hyperspectral instruments used for remote sensing at moderate spatial resolution. Stress is placed on confidence levels that can be achieved, using on- board systems of minimal complexity. The main objective is to record ideas for review in future development programs, with some analysis of their merits.

With the impending launch of several new satellite sensors with thermal channels, there is a renewed interest in evaluating the in-flight calibration of these sensors using ground truth or under flight validation techniques. The relatively rapid temporal variation of surface temperatures, coupled with the increased calibration requirements levied by some of the science applications, place a considerable burden on the calibration team. This paper addresses procedures under development to ensure the rigorous in-flight calibration of satellite sensors in the thermal region. These efforts are directed at Landsat 7, but are intended for use with any thermal sensor and particularly address sensors with multiple spectral channels. The paper addresses laboratory calibration techniques for calibration of transfer radiometers, laboratory calibration of reference blackbodies for use in field or under flight applications, calibration of under flight instrumentation and under flight (vicarious) methods for calibration of space-based instrumentation. The methods are presented in the context of the more limited procedures that were used for under flight calibration of the HCMM and Landsat 4 and 5 sensors. A particular emphasis is placed on the importance of spectral structure in the calibration process which is critical for multi-wavelength or narrow wavelength sensors. The calibration facility at RIT for calibration of the modular imaging spectrometer instrument that will under fly Landsat 7 is described in detail, along with full calibration procedures. Issues associated with selection of target surfaces (size, emissivity, and temporal stability) for vicarious calibration also are discussed, along with our approach for addressing these issues to evaluate the in-flight performance of Landsat 7. Previous efforts have demonstrated that calibration using similar approaches could achieve expected errors of approximately 1 K. This paper addresses refinements designed to significantly reduce the residual errors in the calibration process.

New developments in interference filter technology utilizing low thermal expansion coefficient materials which are deposited free of voids using variants of ion-assisted- deposition techniques have made possible the development of a new class of low-cost, lightweight remote sensing instruments. These instruments can easily have a throughput two orders of magnitude larger than similar dispersive monochromators in addition to having a stray light rejection somewhere between that of a single and a double monochromator for a bandpass of the order of one nanometer. Results from environmental testing, measurements of stability in space, and unique problems associated with spectral radiance calibrations with these interference filter instruments are described.

Vicarious calibration generally requires field activities in order to characterize surface reflectances and atmosphere to unable use the prediction of the radiance at the satellite level. To limit human presence on the field, an automatic ground-based station was defined as well as the required protocol to achieve satellite vicarious calibration. The solar irradiance measurements are self calibrated using the Langley technique. The instrument was designed so that, firstly, the same gun measures both the solar irradiance and the radiance (sky or ground) and, secondly, that the field of view is constant over the spectral range. These two conditions offer an intercalibration opportunity between radiance and irradiance as well as the field of view is well defined. Experimental determination of the field of view is possible in UV region based on the Rayleigh scattering. We, then, describe how to derive the TOA signal from measurements. Two approaches have been developed according the energetic characteristics we want to estimate (reflectance or radiance). Preliminary results of a field campaign in June 1997 are reported.

Rayleigh scattering targets over clear oceans under large solar and viewing angles have proved their efficiency to calibrate remote sensing instruments in the low wavelength channels (AVHRR C1, SPOT-HRV XS1). To obtain a good accuracy, this method needs an evaluation of the different contributors participating in the total TOA signal: aerosol, atmospheric conditions, foam, water reflectance. For instruments such as SPOT or VEGETATION, the near infra red band is used to estimate the aerosol content which is after transferred in the band to be calibrated depending on the considered aerosol type. Two methods are described for the spectral transfer of the aerosol optical depth: one using the interband calibration coefficient and a new one using the absolute calibration coefficient of the near infra red band. Simulations are done to evaluate the performances of these two methods using different extreme cases of solar and viewing zenith angles, wind speed, water vapor content and ozone amount. The results show the method using the absolute calibration coefficient is more accurate.

In microwave remote sensing, chirp transform spectrometers (CTS) have not been widely used compared to other real-time spectrometers like acousto-optical-spectrometers (AOS) or digital autocorrelators (DAC). Recent progress in solid state physics and photolithographic processes has led to the availability of large time-bandwidth-product dispersive delay lines and high speed, low power digital electronics, which both is required to build a competitive CTS. A high resolution state-of-the-art CTS has been developed at our Institute. A functional description is given and its future development potential is discussed and compared with past and recent developments.

The SeaWinds scatterometer instrument is currently being developed by NASA/JPL, as a part of the NASA EOS program, for flight on the Japanese ADEOS II mission in 1999. This Ku-and radar scatterometer will infer sea surface wind speed and direction by detecting the normalized radar backscatter cross section over several different azimuth angles. This paper presents the design characteristics of and operational approach to the instrument itself. The SeaWinds pencil-beam- antenna conical-scan design is a departure from the fixed fan- beam antennas of SASS and NSCAT. The purpose of this change is to develop a more compact design consistent with the resource constraints of the ADEOS II spacecraft. The SeaWinds conical- scan arrangement has a 1-m reflector dish antenna that produces a time-shared dual antenna beam at 40 degrees and 46 degrees look angles. The dual-beam operation provides up to four azimuth look directions for each wind measurement cell. At an orbit height of 803 km, the conical scan provides a broad and contiguous wind measurement swath width of about 1800 km for each orbital pass. The radar has a linear frequency modulation, or chirp, encoded transmitter waveform. The bandwidth of modulation is nominally 375 kHz. For each transmitted pulse, an onboard pulse compression processor will produce 12 measurement cells of 6-km resolution in range and about 26 km in azimuth (cross-track). Key specifications of the SeaWinds instrument and associated trade-offs and performance are described.

Satellite wind scatterometers are microwave radar instruments designed specifically to measure near-surface wind speed and direction over the global ocean. NASA has a long term commitment to ocean wind remote sensing, starting from Seasat- A satellite scatterometer (SASS), through NASA scatterometer (NSCAT), to SeaWinds. SASS was launched in June 1978 and operated for three months. NSCAT was launched on Japan's Advanced Earth Observation Satellite (ADEOS) in August 1996 and SeaWinds will be launched on ADEOS-2 in 1999. As a continuation of the NASA wind measurement program, we are developing a next generation wind vector measurement instrument, called SeaWinds-1B, scheduled to be launched in the year 2003 on Japan's Advanced Earth Observation Satellite- 3 (ADEOS). The purpose of this paper is to present the system parameters and system design of this new instrument. SeaWinds- 1B is a combination of two instruments into a single design: scatterometer, and polarimetric wind-radiometer (WINDRAD). The scatterometer instrument is used as a baseline to continue the active microwave wind measurements. The WINDRAD instrument is incorporated to demonstrate a new concept of wind vector measurements from space using polarimetric radiometer. WINDRAD can also be used to measure the atmospheric attenuation to improve the scatterometer measurement accuracy. Furthermore, the combination of the scatterometer and WINDRAD will improve the accuracy of the wind vector measurements and the skills for removing the wind direction retrieval ambiguity.

SeaWinds-1B is a spaceborne instrument, under design at the Jet Propulsion Laboratory, to accurately measure the speed and direction of ocean surface winds at high resolutions. SeaWinds-1B consists of a scatterometer and a polarimetric wind radiometer. The scatterometer employs range compression to increase the resolution of its sigma-0 measurements. The polarimetric radiometer will be used to verify new techniques of passively measuring wind vectors from space. The SeaWinds- 1B instrument will also be used to investigate the benefits of combining scatterometer and radiometer data to increase the accuracy of resulting wind products. Since SeaWinds-1B is still in the design phase, there are many system design issues which need to be studied. To aid in such studies, a simulation is being developed which will simulate the operation of the spacecraft (attitude and ephemeris), the scatterometer instrument, and the ground data processing system (sigma-0 and wind products). The simulation will provide an estimate of the wind retrieval performance and sigma-0 measurement accuracy of the SeaWinds-1B scatterometer over realistic wind fields and land targets. Perhaps the most important features of any simulation are the considerations that are used to guide its construction. The SeaWinds-1B simulation will incorporate many factors including instrument rf stability, measurement error correlation, geophysical model function errors, and spacecraft attitude stability. Experience from simulations devised for the NASA scatterometer (NSCAT) and SeaWinds scatterometer will be applied to the SeaWinds-1B simulation.

A proof-of-concept (POC) instrument system to measure cloud top height from space using three complementary techniques is presented. These techniques use measurements of (1) thermal infrared (IR), (2) molecular oxygen 'A' band absorption, and (3) filling-in of Fraunhofer lines (the Ring effect), respectively. Combining three techniques is achieved with a single grating spectrograph with bandpass and order sorting filters by measuring 11 micrometer radiation from the zeroth order of the grating for the IR, 750 - 780 nm radiation from the first order for the 'A' band absorption, and 390 - 400 nm radiation from the second order for the Ca K and H Fraunhofer line filling-in effect. The POC system and its measurement results with the POC system are described.

Remote sensing applications including the National Polar Orbiting Environmental Satellite System (NPOESS) require imaging in a multitude of infrared spectral bands, ranging from the 1.58 micrometer to 1.64 micrometer VSWIR band to the 11.5 micrometer to 12.5 micrometer LWIR band and beyond. These diverse spectral bands require high performance detectors, operating over a range of temperatures; room temperature for the VSWIR band 100 K for MWIR, LWIR and VLWIR, these needs can all be met using molecular beam epitaxy (MBE) to grow HgCdTe. The flexibility inherent in the MBE growth technology is its ability to vary the HgCdTe material's bandgap within a growth run and from growth run to growth run, a capability necessary for remote sensing applications that require imaging in a wide variety of spectral bands. This bandgap engineering flexibility also permits tailoring the device architecture to the various specific system requirements. This paper combines measured detector optical and electrical data, with noise model estimates of ROIC performance to calculate signal to noise ratio (SNR), D* or noise equivalent temperature difference (NE(Delta) T), for each spectral band. The SNR, D* and/or NE(Delta) T are calculated with respect to system focal plane specifications, as required for the meteorological NPOESS.

High resolution infrared imaging system calls for very long scanning arrays with several thousands of detectors and high performance. This paper presents the recent technological developments and the electro-optical performances obtained at LETI/LIR (infrared laboratory) on 1500 detector linear HgCdTe arrays working in the 3 - 5 and 8 - 10 micrometer spectral ranges. These very large arrays (length approximately equals 50 mm) have an indirect hybrid architecture composed of butted HgCdTe PV detection circuits and Si CMOS readouts hybridized on a mechanically close-matched fanout substrate. Defect free dicing and butting, respecting the detector pitch, is made by accurate and non damaging techniques.

The recent developments within the ESA funded HRIS (high resolution imaging spectrometer) technology program -- aiming at an airborne demonstrator model -- yielded rather successful subsystem developments. HRIS is designed as a true pushbroom hyperspectral imager with comparatively high spatial and spectral resolution, covering the spectral range from 450 to 2350 nm. The main breadboard units, with a space-near design, are essentially: a TMA (three mirro anastigmat, Carl Zeiss) front optics, a dual path spectrometer optics (Officine Galileo) with a novel in-field spectral separation unit, a 2-D SWIR CMT detector array with a dedicated CMOS readout multiplexer (GEC Marconi IR, MATRA MSF for testing), the signal processing electronics (DSS), some calibration elements (DLR + DSS), and the extensive testing of all units. The paper presents the essential results per unit, with possible exception of the front optics (which may not be completed at the conference paper presentation yet), including derived further development efforts. Also, the remaining steps towards an airborne test mission are outlined, together with a brief description of the envisaged high-altitude aircraft. We hope that this paper may also stir some potential users of later airborne HRIS test missions over dedicated target areas. Positive responses would support ESA to pursue the program. The technology units development under the HRIS contract have turned out useful for follow-on instrument developments such as the ESA Explorer mission candidate PRISM (processes research by an imaging space mission). This leads to the conclusion that the achieved development results are a sound basis for future airborne and spaceborne hyperspectral imager developments in Europe. A brief survey of the current PRISM baseline concept is added to the paper.

The MightySat II.1 satellite carries as one of its primary payloads a Fourier transform hyperspectral imager, the first such sensor to be flown in space. Over the last year the sensor has passed its preliminary design and an engineering model of the sensor has been constructed. The model has started to be qualified. To date the sensor has met its weight, volume and power design goals. An unusually high random vibration qualification level has forced the redesign of two mirror mounting techniques. Custom, space qualified, VME electronic camera interface and control cards to handel 20 Mbytes/sec of imagery data has been designed, fabricated, and coupled to a set of four C-40 processors to provide 160 MIPS of onboard processing. Mission operations are now being developed that will demonstrate a 30 m GSD by using the on orbit three axis maneuvering capability of the satellite. The payload is on schedule for a delivery in early 1999 for integration on the bus.

Kestrel Corporation has designed and is now building a dual- band infrared Fourier transform ultraspectral imager for aircraft deployment. Designed for installation in a Cessna 206, this instrument will have a 15 degree FOV, with an IFOV of 1.0 mrad. The target spectral resolution is better than 1.5 cm^-1 over 2000 to 3000 cm^-1 and 0.4 cm^-1 over 850 to 1250 cm(superscript -1$. using 512 spectral channels. The device will use a variety of spectral enhancement techniques to achieve this unprecedented spectral resolution. Computer simulations of the optical systems demonstrates sub-wavenumber resolutions and signal to noise ratios of over 900.

Spaceborne Fourier transform spectrometers (FTSs) are one of the most promising sensors for global measurements of the atmosphere and/or the surface because of its potentialities for high spectral resolution and high accuracy. One of the difficulties for realizing a high performance FTS is how to overcome its performance degradation caused by disturbances such as mechanical vibrations and shocks. We have developed a computer-based simulator to evaluate the performance degradation. Influence of vibrations for various kinds of FTSs using different optical elements and different sampling methods are examined by evaluating spectral measurement errors quantitatively. It is shown that spectral measurement errors of FTSs is restrained by using corner cube reflectors and sampling method defined by laser interference.

A great effort is actually devoted to design and to develop new remote sensing instruments with increased spectral and spatial resolution. This effort is aimed to obtain a direct and sure target recognition relying on identification of narrow features in the reflectivity spectrum of the observed targets. VIRS is a promising instrument for airborne hyperspectral remote sensing. The sensor is one of the first imaging spectrometers operating in push-broom mode, and provides 20 independent channels selected among 240 possible bands distributed between 400 and 1000 nm. Each channel has a spectral resolution of 2.5 nm and a digitalization accuracy of 10 bit. The main problem for application of hyperspectral remote sensing to environmental studies is that most of the available theoretical models were derived for low resolution spectral measurements. These models do not take advantage of the huge information gathered by such a sensor as the VIRS. In this paper the problem of modeling and interpreting hyperspectral remotely sensed data acquired by the VIRS is examined. The paper shows the main technical characteristics of the sensor, and investigates its use for environmental monitoring. Our work shows the lack of reliable models for theoretical interpretation of data as well as the need for higher spectral resolution data in some specialized applications.

The edge of the moon is used to offer a high contrast target to perform a visible 'knife-edge' MTF test on a digital imaging system in geostationary orbit. An image of the moon is taken in the camera's normal scanning mode, and traces across the sharpest edge are used to form an edge spread function (ESF). The ESF is then used to produce an MTF estimate. In a second trial, the imaging system is allowed to stare as the lunar edge drifts by, creating an edge spread function with a much higher effective spatial sampling rate. In each case, a technique of combining and resampling traces is employed to adapt the knife-edge MTF technique for use with sampled data. The resulting MTF curves track four ground test frequencies to within five percent. The approach thus offers a means of testing the MTF and OTF of orbiting image acquisition devices.

The geostationary Earth radiation budget (GERB) instrument is scheduled to be launched on the Meteosat Second Generation (MSG) series of satellites with the intention of measuring the total radiative energy output of the Earth to an accuracy of 0.5%. Although the footprint of a pixel of the GERB detector is 44 km square at the sub-satellite point, it is necessary to locate the position of a pixel to 3 km. This paper discusses why this is necessary and how it will be achieved. It describes the instrument, the techniques used to achieve the high positional accuracy and the data processing system that will generate the data products.

The satellite UV NO-O₂-O₃ robust integrating spectrometer experiment (SUNRISE) will develop highly sensitive spectrometers for satellite solar limb measurements. The first of our satellites will be launched in mid-2000, and will carry a test spectrometer called OPUS-1 which will accurately monitor the solar Lyman (alpha) during a period its normal coverage will be otherwise disrupted. It will be mounted alongside a series of more complex spectrometers, called OPUS-2 . . .. These will measure oxygen photolysis with the sun as an occulted UV light source. Inverse Abel transforms produce vertical target profiles in 3 km bins each sunrise and sunset. Our system can resolve the Schumann-Runge lines because we have devised ways to reduce greatly the systematic errors in our measurements with excellent systematic checks and system redundancies: Perhaps the most importantly, we get exoatmospheric spectra obtained immediately after sunrise and before sunset to give an excellent spectral calibration. We aim to measure O₂ photolysis down to approximately 43 km. The SUNRISE collaboration has taken a fast, simple and robust route to the important measurements we have targeted. The satellites are in eccentric equatorial orbits at 800 km, with severe constraints on payload and power availability. The expected lifetimes of these satellites (8 - 15 years) offers unprecedented opportunities in UV-measurements and in ozone monitoring (for example, in spanning a sun-spot cycle) but places great demands on the robustness of our equipment. Our OPUS technology reflects that. Given that ozone has such a central role in atmospheric science, and that recent uncertainties (based on HALOE observations) in actual ozone deficits about 40 km have led to great uncertainties in atmospheric models, the precise measurement of O₃ production and O₃ sinks is very important. Our spectral range extends from 120 nm to 124 nm, in OPUS-1, and so we also will target the Lyman (alpha) line, which will allow real-time measurements of solar variability, and will in any case provide an excellent built in calibration, and 175 - 225 nm in OPUS-2. We can make significant measurements of NO absorption in the altitude range 40 km upwards with vertical resolution approximately 3 km and accuracies of approximately 10%. By establishing the levels of absorption in ozone, and comparing with the exoatmospheric measurements, we furthermore measure actual concentrations of ozone. SUNRISE therefore offers a unique tool making the simultaneous measurement of ozone production, concentrations, and a major mechanism of its loss, through the NO cycle. SUNRISE introduces an innovatory range of technologies, individually well-understood, the combination of which results in potentially large improvements in sensitivity and spectral selectivity.

The geostationary tropospheric pollution satellite (GEO TROPSAT) mission is a new approach to measuring the critical constituents of tropospheric ozone chemistry: ozone, carbon monoxide, nitrogen dioxide, and aerosols. The GEO TROPSAT mission comprises a constellation of three instruments flying as secondary payloads on geostationary communications satellites around the world. This proposed approach can significantly reduce the cost of getting a science payload to geostationary orbit and also generates revenue for the satellite owners. The geostationary vantage point enables simultaneous high temporal and spatial resolution measurement of tropospheric trace gases, leading to greatly improved atmospheric ozone chemistry knowledge. The science data processing, conducted as a research (not operational) activity, will provide atmospheric trace gas data many times per day over the same region at better than 25 km ground footprint. The high temporal resolution identifies short time scale processes, diurnal variations, seasonal trends, and interannual variation.

The SFINX instrument (SRON Fabry-Perot interferometer experiment) is a high resolution spectrometer for the far infrared, designed for balloon operation. It is composed of a small telescope and a cryogenic detection system. The liquid helium cryostat houses a Fabry-Perot with a spectral resolution in excess of 6000, of which the orders are separated by a grating monochromator, and a Ge:Ga photon detector. An additional liquid nitrogen dewar contains a recently developed bolometer with high Tc temperature sensor. Vertical sky resolution is ca 5 milliradian. Together with the proven MIPAS mid-infrared interferometer, the SFINX instrument will be flown in several balloon campaigns to obtain a more complete picture of the stratospheric composition with, in addition to current satellite data, detailed information of its changes during sunrise. The presentation discusses the hardware design and a number of details about the SFINX experiment.

In the field of the scientific cooperation between our two Institutes started in 1986, a common research program was developed for the analysis of the characteristics and the application of advanced spaceborne optical sensors for the remote sensing of the Earth. This program has become a part of the international scientific project PRIRODA. The space module PRIRODA is the technical base for the project. It was launched, and attached to the inhabited space platform MIR in April 1996. By means of the optical sensors placed on board of the PRIRODA module, we are going to study the geophysical parameters useful for environmental monitoring and resources evaluation. The principal attention is paid to the study of the following topics: (1) water quality in the coastal zone and particularly near the river estuaries; (2) vegetation stress due to the anthropogenic activities; (3) geophysical studies in areas of geothermal and volcanic activities; (4) estimation and verification of the atmosphere contributions. In order to perform the goals mentioned above, the Italian side has identified some test sites mainly in the Tuscany region and the data from the following optical sensors of the PRIRODA module, will be utilized: (1) ISTOK-1, the instrument is a 64-channel infrared spectro-radiometer in the band of 4 - 16 micrometer to measure both the atmospheric transmittance spectrum by looking at the Sun and the thermal emission spectrum of the atmosphere and the Earth surface under different angles of pointing. In addition the instrument includes a TV CCD camera to observe the clouds and the Earth surface (2) MOS-OBSOR, this imaging spectrometer is dedicated to the investigation of the reflected solar radiation in the atmosphere -- Earth surface system in the visible and near infrared ranges. The apparatus consists of different optical blocks and is comprehensive of on-board data compression. (3) MOMS-2P, this modular optoelectronic multispectral stereo scanner consists of two subunits: a threefold stereoscopic imaging system and a four-band multispectral camera with nadir orientation. The instrument parameters were designed in order to fill the gap between existing spaceborne system and airborne photography. (4)MSU-E, this electro-optical scanner is mainly devoted to investigate the reflected solar radiation in the 'atmosphere -- Earth surface' system at a spatial resolution of 25 m in three visible and near infrared spectral bands. (5) MSU-SK, this opto-mechanical scanner operates in four adjacent visible and near infrared bands at 120 m of spatial resolution plus one band in the thermal infrared region with 300 m of spatial resolution. An additional feature consists of the possibility to tilt the field of view of the scanner up to 30 degrees in the plane normal to the flight direction. Preliminary results, coming from the data collected by these sensors, are presented, discussed and compared with the data collected by field experiments on the test areas overflight by the MIR.

The field of Earth remote sensing is evolving from one that contains purely governmental and military standalone systems of high complexity and expense to one that includes an increasing number of commercial systems, focused missions using small satellites, and systems of lower complexity and cost. The evolution of the field from 1980 - 2007 is summarized in this paper, with emphasis on the rapid changes of international scope that are taking place in 1997 which will shape the future of the field. As of three years ago, seven counties had built and flown free-flying earth observation satellite systems. Projections are for the number of countries operating such systems to approximately double by three years from now. Rapid changes are taking place in terms of spatial resolution, spectral resolution, proliferation of small satellites, ocean color, commercialization and privatization. Several fully commercial high-resolution systems will be launched over the next three years. Partly commercial synthetic aperture radar (SAR) systems became a reality with the launch of Radarsat in 1995. Only a handful of small satellite remote sensing missions have been launched to date, while a large number will be launched over the next few years, including minisats from Australia, Brazil, Israel, Italy, South Korea, Taiwan, Thailand, and the USA, as well as microsats from many countries including Malaysia, Pakistan and South Africa. Systems with far greater spectral resolution will also become a reality as hyperspectral instruments are launched. In 1997, we truly stand on the cusp of tremendous change in the burgeoning field of Earth remote sensing.

An infrared sensor dedicated to surface temperature monitoring at medium scale (250 m) has been defined within the MUST mission study. This mission is dedicated to applications in agriculture, irrigation, hydrology, forest fires and environment. The work is performed within the frame of the European Commission (DG XII) contract. The study is led by Matra Marconi Space with CEMAGREF (F), the University of Valencia (Spain), the CNRS/CETP (F), INFOCARTO (Spain) and NRSC (UK) as partners. The definition of the mission and of the instrument has been performed in closed loop with the user community in order to match the instrument performance with the users' needs. A traditional scanner concept using cryogenically cooled photoconductor detectors and a more innovative push broom concept using linear arrays of uncooled microbolometers have been studied. Both concepts satisfy the users' needs and provide quite equivalent performance. The push broom option has been selected because it does not require any cooling, and is free of micro-vibrations. The concept is fully compatible with an implementation as a passenger on SPOT5 and is quite complementary of the vegetation instrument of SPOT5. The instrument offers a swath width of about 1400 km. It provides two spectral channels around 11 and 12 micrometer wavelength optimized to correct the atmospheric effects by the split window method. The NEDT is in the range of 0.3 K. This allows a final accuracy on land surface temperature of about 1.5 K after emissivity and atmosphere corrections which is fully adequate for the foreseen applications.

The most accurate instrument for spacecraft attitude determination is a star tracker. Generally, these are CCD- based instruments. Until recently, only first-generation units were available. However, these first-generation designs are limited to outputting positions of a few stars in sensor- referenced coordinates and require extensive external processing. Fortunately, advancing technology has enabled the development of a new second-generation class of star trackers. These designs are fully autonomous, solve the lost-in-space problem, have large internal star catalogs, use many stars for each data frame, have higher accuracy, smoother and more robust operation, potentially lower cost, and output attitudes which are referenced directly to inertial space without any further external data processing. Two currently available designs which are in production and meet these requirements are the AST-201 from Lockheed Martin Missile & Space and the ASC from the Technical University of Denmark. The first design is in the general size, power, mass, and reliability class of typical, conventional star trackers. The second one features reduced size, power, mass, and cost, with commercial off-the- shelf components. Second-generation star trackers have a promising future with a likely evolution to low cost, miniature, stock instruments with wide application to a growing variety of space missions.

Emerging technologies and micro-instrumentation are changing the way remote sensing spacecraft missions are developed and implemented. Government agencies responsible for procuring space systems are increasingly requesting analyses to estimate cost, performance and design impacts of advanced technology insertion for both state-of-the-art systems as well as systems to be built 5 to 10 years in the future. Numerous spacecraft technology development programs are being sponsored by Department of Defense (DoD) and National Aeronautics and Space Administration (NASA) agencies with the goal of enhancing spacecraft performance, reducing mass, and reducing cost. However, it is often the case that technology studies, in the interest of maximizing subsystem-level performance and/or mass reduction, do not anticipate synergistic system-level effects. Furthermore, even though technical risks are often identified as one of the largest cost drivers for space systems, many cost/design processes and models ignore effects of cost risk in the interest of quick estimates. To address these issues, the Aerospace Corporation developed a concept analysis methodology and associated software tools. These tools, collectively referred to as the concept analysis and design evaluation toolkit (CADET), facilitate system architecture studies and space system conceptual designs focusing on design heritage, technology selection, and associated effects on cost, risk and performance at the system and subsystem level. CADET allows: (1) quick response to technical design and cost questions; (2) assessment of the cost and performance impacts of existing and new designs/technologies; and (3) estimation of cost uncertainties and risks. These capabilities aid mission designers in determining the configuration of remote sensing missions that meet essential requirements in a cost- effective manner. This paper discuses the development of CADET modules and their application to several remote sensing satellite mission concepts.

The beginning of the next millennium promises an explosion in the quantity and quality of global data available from imaging remote sensing systems. The scientific and commercial communities become aware of unique hyperspectral imaging data acquisition opportunities. A brief profile of over 80 high resolution spaceborne and airborne earth observation sensor systems (H less than 800 km) planned to be operating in the year 2000 and beyond are presented in this paper. This overview covers multi- and hyperspectral civil, land and ocean nadir viewing observation sensors in the spectral range from the ultraviolet to the thermic infrared. A summary of the performance of each system, from image parameters (spectral and ground resolution) to the image generating procedure (spectral selection mode, image acquisition mode) is presented. At this point some caution is due since not all these concepts and plans will come to pass. The cuts in the government budget and the containment of commercial plans for new sensor systems will affect the realization of the present plans. However, the year 2000 will see at least four large area vegetation and ocean mappers, three landsat-like systems and two commercial high resolution systems in polar orbit simultaneously. A fleet of over 40 airborne sensor systems gives the final polished form of the future data acquisition opportunities.

The present work describes the modeling and the simulation of a concept of novel sensor-single tube color image intensifier intended for direct observation of the night side of the Earth or other planets in the visible range of the spectrum from orbit, or as airborne sensor or as color image preamplifiers for color CCD sensors. The color image sensor consists of an objective and microchannel tube which contains an input multielement color filters pattern, matched and registered with output multielement color filters pattern. Input/output color filters patterns, which determine the spatial sampling of the image, were organized both in hexagonal RGB mosaic and in RGB stripes configuration. The present work is aimed at describing the basic theoretical models for simulation and analysis of the color image sensor including quantification and optimization of its performance. The basic models include the major color intensifier parameters, namely, spectral characteristics of the color filter elements, their size and spacing; spectral characteristics of the photocathode and phosphor; MCP's pore size, center-to-center spacing and gain; voltages and distances of spacing photocathode -- MCP_in and MCP_out -- screen; tolerance of registration of input- output filters, etc. For a number of technologically achievable parameters it is shown that: (1) the resolution of the device, based on the Nyquist frequency for hexagonal mosaic filter configuration can reach approximately 20 color (line pairs)/mm; for stripe filter configuration it can reach approximately 30 color (line pairs)/mm along stripes and approximately 10 color (line pairs)/mm across stripes with adequate MTF; (2) the light non-uniformity is less than 5% which is insignificant; (3) realistic set of filters provides a good color transformation -- compatible to the transformation in color CRT displays. The model also describes the color edge transformation. As it was shown, cross-talk level in single basic color element from neighboring elements is about 6%, and its influence is expressed in moving the color coordinates of a uniform color on the tube's output toward the 'white point' on the CIE chromaticity diagram. Modeling showed that color imaging can be achieved at very low light levels with good color resolution and color preservation. The first color images were successfully obtained from a prototype, demonstrating that the proposed concept indeed produces a color vision image intensifier device with good color imaging abilities. The computer simulation agrees well with photometrical and colorimetrical parameters of the first workable prototypes.