The German 'Atmospheric and Environmental Research Satellite, ATMOS'-program has been started in early 1989 under responsibility of the DLR. It is concerned with the measurement and analysis of atmospheric trace gases for the investigation of the ozone layer disturbance and the amplification of the greenhouse effect as well. Marine and terrestrial biosphere observation additionally is of great interest because of dramatically increasing human impact on the environment. The paper deals with the description of the scientific objectives of the ATMOS mission with focus on the tropospheric and stratospheric exchange processes, the chemistry of trace gases and the interaction of the biosphere and atmosphere. An optimized orbit concept is proposed and a comprehensive data management and information system is introduced. The space segment consists of a modular platform accommodated by a service module and a payload module with some growth potential to be open for involvement of international partners. The measurement principles of the four basic ATMOS instruments are described and their configurations are illustrated due to the present development status.

The BEST mission which is part of the Global Energy Water Experiment (GEWEX) program is described. To accurately evaluate the energy variations of the tropical system it is proposed to group a set of instruments on a low altitude, low inclination platform. The BEST mission will simultaneously measure wind field through a Doppler radar, precipitation through a pulsed radar, earth radiation through a radiometer, and eventually water vapor profile through a differential absorption lidar.

A new concept for a polar orbiting satellite dedicated to global change research and its extension to fulfill the meteorological operational mission in the morning orbit is studied by CNES and MATRA, with the support of EUMETSAT and a group of European scientists. Two options were investigated during the feasibility study called GLOB(MET)SAT, the first one, GLOBSAT, restricted to an IGBP-dedicated mission, and the second one, GLOBMETSAT, combining this research mission and the operational met-mission specified by EUMETSAT. The mission objectives, the associated requirements, and the instruments accommodated are presented and discussed, as well as the main results of the phase A study for the space segment. The system configurations, characteristics, performances and the development plan are described. Both options prove feasible and compatible with a target launch date in the 1996-97 timeframe and preserve a significant growth potential. The use of the MK-2 platform developed for the SPOT-4 program and of other recurrent hardware elements appears a significant cost-saving, schedule-securing and reliability factor in both options. In the same line, the GLOBMETSAT system combining the environment and meteorological missions is of mutual benefit for both missions, in terms of reliability, cost sharing and use of platform resources, while keeping each mission independent and unaffected by the other.

Meteosat Second Generation is the planned successor to the current ESA/Eumetsat program of meteorological satellites known as Meteosat Operational. This paper reviews the background to Meteosat Second Generation, covering the satellite and payload studies conducted since 1984 on several types of missions and satellites, and it reviews the requirements for the mission as it is now defined with a spin stabilized platform.

The overall scenario of ESA earth observation polar platform program is reviewed with particular attention given to instruments currently being considered for flight on the first European polar platforms. The major objectives of the mission include monitoring the earth's environment on various scales; management and monitoring of the earth's resources; improvement of the service provided to the worldwide operational meteorological community, investigation of the structure and dynamics of the earth's crust and interior. The program encompasses four main elements: an ERS-1 follow-on mission (ERS-2), a solid earth gravity mission (Aristoteles), a Meteosat Second Generation, and a series of polar orbit earth observation missions.

Current SPOT-4 technical mission research and development programs concentrate on an increase in geometrical resolution amounting to pixel size of or less than 5 meters; along-track stereo imagery based on two images from the two cameras obtained in a few seconds; and continuity of the SPOT service. Modifications to be made to the camera design include the optical combination for a high quality image to 1.6 micron and development of large band visible and MIR optical coating; development of a 3000-point detector for the MIR band; complete rearrangement of the focal plane; complete redesign of the video electronics to eliminate interference and correct obscurity signals; and installation of active temperature control on the MIR channel.

The selected optical payload for the future Meteosat second generation satellites (MSG) is a spinning enhanced vis-IR imager (SEVIRI). This instrument will provide full earth disk images every 15 minutes with 3 km spatial resolution (sampling distance) in 11 visible and IR spectral channels, and 1 km in a dedicated high resolution visible channel. The foreseen set of spectral channels includes the visible and IR atmospheric windows, two water vapor channels, and three narrow IR bands at 4.5, 13 and 14 microns also called pseudo-sounding or instability channels. This paper presents an overall description of the instrument and recalls the technical trade-offs which have lead to select this approach through several pre-phase A studies.

A Scanning Radiometer for Radiation Balance (ScaRaB) to be flown on a series of METEOR-3 Soviet polar orbiting weather satellites is described. The radiometer comprises 2 broad channels (0.2-50 microns, 0.2-4 microns) for radiation budget, and two narrower bands (0.5-0.7 micron, 10.5-12.5 microns) for scene identification, with spatial resolution at nadir of about 50 km. The set of on-board sources includes blackbody simulators for the calibration of long-wave channels, and tungsten filament lamps and mosaic array diffusers for short wave calibration. A specific filtering scheme protects solar diffusers and lamps from the impact of thermal environment during calibration of the 0.2-50 micron channel.

The Medium Resolution Imaging Spectrometer (MERIS) is an optical instrument which is intended to be flown on the first European Polar Platform, scheduled for launch in 1997. The instrument has a spectral range of 400 nm to 1050 nm, a swath width of 1500 km, a spectral resolution of 1.25 nm and spatial resolution of 250 m. The instrument has applications in the fields of oceanographic, land and atmospheric research.

MIPAS is a high-resolution limb sounding Fourier spectrometer, designed to measure atmospheric trace gases in the medium and thermal infrared from the upper troposphere to the thermosphere. The main scientific objective of MIPAS is to obtain more precise data on the composition, dynamics, and radiation from the tropopause to the mesosphere. Specific measurement goals of the MIPAS experiment are the ozone chemistry and monitoring of the major greenhouse gases on a global scale, as well as the investigation of dynamic transport phenomena and the middle atmosphere radiation field. MIPAS has been conceived in harmonized feasibility and definition studies for two programs: the European Space Agency's Earth Observation Preparatory Program for the first Polar Orbiting Earth Observation Mission (POEM-1) and the German environmental research satellite program ATMOS.

The Optical Mapping Instrument (OMI) is a space-based Earth observation system being developed to collect data from which medium-scale mapping of high quality can be produced. In this paper, consideration is first given to existing and planned optical Earth observation systems, and it is noted that the topographic mapping market is not well served by these instruments. The requirements of this topographic market are examined, and the specification of an instrument to meet this market demand are derived. A brief overview of the OMI system meeting these requirements is given. Finally, specific aspects of the design concerning optics and detectors are presented in more detail.

As a part of the payload of the first European polar platform, the GOMOS instrument has been proposed by a group of 25 scientists from six countries. It consists of a telescope feeding two spectrographs and mounted on a dedicated steerable platform. The transmittance of the atmosphere between 250 and 950 nm is measured by comparing the spectrum of a star outside the atmosphere, and through it. The ozone tangential column is determined from its UV and Chappuis band absorption. This self-calibrated method is particularly well suited for the study of the long-term ozone trend. The altitude of each single measurement is precisely known (+/- 50 m), independently of attitude uncertainties. The instrument, as defined in the course of an industrial phase A study, is presented in some detail. About 25 stellar occultations per orbit, and 350 per day, spread over all latitudes can be performed from 90 km down to 15-20 km of altitude. NO2, NO3, H2O, T(z), and aerosols are also simultaneously determined, important parameters associated to the ozone equilibrium. Over a period of 4 years in orbit, GOMOS should be able to detect a linear decrease trend of 0.05% per year in 10 bands of latitude.

The Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) is an instrument which measures backscattered, reflected and transmitted light from the earth's atmosphere and surface. SCIAMACHY has eight spectral channels which observe simultaneously the spectral region between 240 and 1700 nm and selected windows between 1940 and 2400 nm. Each spectral channel contains a grating and linear diode array detector. SCIAMACHY observes the atmosphere in nadir, limb, and solar and lunar occultation viewing geometries.

The POLDER experiment is described which is aimed at providing data on the atmosphere, vegetation, and oceans on the basis of the polarization and directionality measurements of solar radiation reflected by the Earth-atmosphere system. Design of the POLDER instrument is presented which is based on CCD matrix imaging through a large field of view lens. The instrument takes 15 images on a 2D detector through the successive windows of the filter wheel, then waits for an increase of the viewing angles by about 10 deg before taking another sequence of images.

Optical sensor system capable of acquiring earth image data in visible, near-infrared, and shortwave-infrared region in 7 spectral bands, with spatial resolution of 18 x 24 m is described. In the near infrared band it provides stereoscopic images on the same orbit. In the shortwave-infrared region of 1.5-2.4 um it operates in the range of 4 bands to identify minerals and rocks.

A cooling system has been developed for a short-wave infrared radiometer (SWIR) charge coupled device (CCD) sensor tobe carried aboard the Earth Resources Satellite (JERS-1). The system's Stirling cycle cryocooler is capable of cooling the CCD sensor to liquid nitrogen temperature from a room temperature in 20 min or less with power consumption of 153 W or less.

This paper deals with the spaceborne synthetic aperture radar (SAR) to be launched on the Japanese Earth Resources Satellite-1. The SAR is to be operated in L band. Mission purpose is mainly dedicated to geological applications. The ground resolution of the processed image is to be 18 m. Off-nadir angle is 35 deg. Key system parameter design and performance are presented.

The Advanced Earth Observing Satellite (ADEOS) installs eight sensors for earth observation, including two core sensors developed by the National Space Development Agency of Japan (NASDA). ADEOS is planned to develop Japanese earth observation technology and to contribute to international monitoring of global environmental change of the Earth. The ADEOS program is now in phase C (basic design phase). Preliminary design review was held in summer 1991.

Design of the OCTS, a high-precision remote-sensing instrument for NASDA's Advanced Earth Observing Satellite (ADEOS) for simultaneous measurements of the ocean color and sea-surface temperatures, is presented. The OCTS uses a rotating mirror to scan a swath of the earth 1400 km wide from sun-synchronous orbit at 800 km altitude. It is planned to be placed into orbit in 1995 to provide 3 Mbps image data for visible to thermal infrared spectral range, in 12 bands.

The Ocean Color and Temperature Scanner (OCTS) is a piece of observation equipment that measures ocean color and temperature from a scientific satellite. The OCTS is equipped with two focal plane assemblies: one observes ocean color in the range of visible to near infrared, and the other measures ocean temperature in the infrared region. We report here results of the so-called break boad model of the latter focal plane assembly. This focal plane assembly contains four infrared detectors that are cooled to 100 K by radiational cooling. We have evaluated this cooled focal plane assembly, and have confirmed that it has satisfied such NEP (noise equivalent power) values, registration accuracy and power consumption as are required in view of the OCTS performance characteristics.

The current status of an advanced visible and near infrared radiometer (AVNIR) planned to be launched onboard Advanced Earth Observing Satellite in 1995 is described. The AVNIR is intended to observe land and coastal zones to monitor different phenomena including desertization and destruction of tropical forest.

Interferometric monitor for greenhouse gasses (IMG) based on an infrared Fourier transform spectrometer (FTS) is described which is scheduled to be launched onboard the Advanced Earth Observation Satellite (ADEOS) in 1995. The IMG uses the 10 cm aperture Michelson interferometer with a 10 cm traveling scanning mirror and 3 band detector at an operating temperature of 80 K or less which is maintained by the Stirling cycle mechanical cooler. The IMG is characterized by a wide spectral band of 700-300/cm and high spectral resolution of 0.1/cm. It is intended for the global investigation of the greenhouse effects, temperature sounding, air pollutions and gaseous exchange between the troposphere and the lower stratosphere.

The ILAS and RIS instruments for Advanced Earth Observing Satellite intended to perform laser absorption measurements are described. The ILAS measurements will provide vertical profiles of ozone and ozone-related species in the polar regions. The RIS will obtain vertical profiles of ozone, carbon dioxide and methane as well as column density of some greenhouse gases based on laser absorption measurements.

ASTER is an advanced multispectral imager with a high spatial, spectral and radiometric resolutions for EOS-A platform. ASTER covers a wide spectral region from visible to thermal infrared by 14 spectral bands. Moreover, ASTER has a stereoscopic viewing capability by a near infrared band. Significant design challenges are realization of a pushbroom type visible and near infrared radiometer (VNIR subsystem) with a high spatial resolution of 15 m, a pushbroom type short wave infrared radiometer (SWIR subsystem) with high spectral resolution and a whiskbroom type thermal infrared radiometer (TIR subsystem) with a high spatial, spectral and radiometric resolutions. Long life mechanical coolers for the SWIR and the TIR subsystems are also components with a technical risk.

Preliminary design and basic performance of the VNIR and CSP subsystems of the ASTER instrument for the EOS-A platform is discussed. The VNIR is characterized by the high spatial resolution of 15 x 15 m and stereoscopic imaging in the 0.76-0.86 micron band. It corrects the geometric aberration caused by the rotation of the earth and calibrates the radiometer with the halogen lamps on orbit. The CSP is based on a signal processor which multiplexes system telemetry for image data, packetizes image data in CCSDS format, converts parallel signals into serial, and controls output to EOS-A transfer frame generator.

The SWIR subsystem based on a multispectral imaging radiometer with 6 observation bands in the region of 1.5-2.5 microns and a ground resolution of 30 m is described. This subsystem in conjunction with other two imagers is integrated into Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) of the EOS-A platform.

A thermal infrared radiometer (TIR) of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is presented which is scheduled to be launched aboard EOS-A of NASA's polar orbiting platform in 1998. The TIR radiometer will provide data on geology, mineral resources, meteorology, and oceanography.

Calibration concept of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) for EOS-A platform is presented. Emphasis is placed on the instrument characteristics to be used for quantitative data analysis which include response linearity, spectral profile of responsivity, polarization characteristics, size-of-source effect, element-to-element responsivity ratio, band-to-band responsivity ratio, and absolute spectral band responsivity. Attention is also given to prelaunch and in-flight calibration for visible infrared, short-wave infrared, and thermal infrared subsystems and a new scheme for cross calibration of ASTER.

Two long life mechanical cryocoolers for the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) instrument of the EOS-A platform are intended to cool down infrared detectors for short-wave infrared and thermal infrared bands. The ASTER cryocoolers based on a split-Stirling cycle have to meet the requirements of a long operation life of 50,000 h and low mechanical vibration.

The JPOP concept, which is part of International Polar Orbiting Platform program, is reviewed. Particular attention is given to the strategy of the JPOP program, observational requirements, strawman candidate sensors, an earth observing scenario, and JPOP system study.

An ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) simulator is described which is designed to simulate visible, near infrared, and thermal infrared (TIR) bands. The ASTER simulator will be applied to geological mapping, refinement of the specifications for ASTER, exploration of the mid-wavelength infrared spectral region, and climatic modeling.

JERS-1 is an earth observation satellite to be launched in February of 1992. The fundamental concept of the JERS-1 is to develop a satellite equipped with geologically-oriented sensor systems truly based upon user's requirements. The JERS-1 is expected to provide world-wide high resolution, whicb will be useful for not only non-renewable resources exploration, but also agriculture, forestry and fishery, disaster prevention, environmental monitoring, and so on. ASTER is a research facility instrument to be onboard the AS's FDS-A platform in 1998, and inherits the technologies developed for the JERS-1. The ASTER instrument will provide valuable data for EOS key science tasks such as surface compositional mapping and surface process quantification and/or monitoring.

MOMS-02/D2, as a continuation of MOMS-01, has been developed for digital mapping of the Earth's surface from space. The camera will be flown on-board the second German Spacelab Mission D2 which is presently scheduled for launch in September 1992. The special characteristic of this camera is the combination of high-resolution panchromatic images for 3- dimensional geometric information with multispectral images for thematic applications. With this concept MOMS-02 is fundamentally different from all existing remote sensing systems and thus pursues new and independent goals.