Terra satellite
The paper in the 11th MEDIAS newsletter describing the LANDSAT 7 satellite mentioned the imminent launch of the TERRA satellite. Indeed, TERRA was successfully launched on December 18th, 1999, the day when our letter was sent to its printer.
The TERRA satellite was previously known as EOS AM-1, since it is the first EOS satellite on a "morning" sun-synchronous orbit, crossing the equator at 10:30 local time (descending node) and a 705 km altitude. The Earth Observing System (EOS) is the centerpiece of NASA's Earth science program and its contribution to US Global Change Research Program, a consensus interagency plan. This program is the national contribution to the international efforts to advance our knowledge of both natural and human-induced global change and understand the earth as a system, including setting up an Integrated Observing Global Strategy (IGOS). EOS is a suite of spacecraft and interdisciplinary science investigations dedicated to advancing our understanding of global change, and includes EOSDIS, a ground-based system which provides the total ground system for archiving, processing and distributing science data from all the EOS spacecraft.
Terra, the flagship EOS satellite namely provides key measurements of the physical and radiative properties of clouds; air-land and air-sea exchanges of energy, carbon, and water; trace gases; and volcanoes, through the observations made by the five following instruments.
ASTER ("Advanced Spaceborne Thermal Emission and reflection Radiometer") is an imaging radiometer, collecting high resolution images of the Earth in the visible, near infrared (VNIR), shortwave-infrared (SWIR) and thermal infrared (TIR) regions of the spectrum. It results from a cooperative effort between NASA and MITI (Japan's Ministry of Trade and Industry), and is managed by JAROS (Japan Resources Observation System Organization). ASTER consists of three distinct susbsystems : VNIR (two cross-track pointable telescope, one that looks backwards and one that looks at nadir , in three spectral bands with 15 m resolution and 60 km swath width), SWIR (30 m resolution, 60 km swath with, 6 SWIR channels), TIR (90 m resolution, 60 km swath with, 5 TIR channels). The ASTER instrument operates for a limited time per org bit (8 minutes in average).
CERES ("Clouds and the Earth's Radiant Energy System") consists of two high accuracy broadband scanning radiometers that measure the Earth's balance and provide some cloud property estimates. Each instrument has three channels (a short-wave channel, a long-wave channel, a total channel). TERRA carries two identical instruments: one operating in a cross-track mode and the other in a biaxial scan mode. The first instrument essentially continues the measurements of ERBE (Earth Radiation Budget Experiment) and TRMM (Tropical Rainfall Measurement Mission) while the second one will provide angular flux information, allowing to improve the accuracy of earth's radiation balance models. CERES is provided by NASA, built by TRW, managed by the Langley Research Center.
MODIS ("MODerate-resolution Imaging Spectroradiometer") will view the entire surface of the Earth every 1-2 days, making observations of land and surface temperature, primary productivity, land surface cover, clouds, aerosols, water vapor, temperature profiles, and fires in 36 co-registered and accurately calibrated spectral bands in the 0.4 - 14.4 µm wavelength domain. Its spatial resolution ranges from 250 m to 1 km at nadir, its viewing swathwith is 2330 km. MODIS is a facility instrument provided by NASA, built by Hughes Corporation and managed by the Goddard Space Flight Center (GSFC).
MOPITT ("Measurements of Pollution in the Troposphere") is designed to enhance our knowledge of the lower atmosphere and observe how it interacts with the land and ocean biosphere, focussing on the distribution, transport, sources and sinks of CO and CH4 in the troposphere. The instrument is a scanning radiometer, 22 km nadir resolution, 640 km swathwith, measuring upwelling and infrared radiance in three absorption bands of CO and CH4 (2.3, 2.4 and 4.7 µm). The accuracy of CO measurement is expected to be 10% with a 3 km vertical resolution, while the CH4 column measurement is expected to be better than 1%. MOPITT is managed by the Canadian Space Agency (CSA), and built by COM DEV Ltd.
Building and successfully launching a sophisticated scientific satellite is indeed a great success. It is nevertheless not so useful within the framework of an international cooperation for global change comprehensive studies if data are not carefully validated and distributed to the widest scientific community through the most modern media. A quite comprehensive calibration and validation strategy of the TERRA instruments - and beyond of the whole EOS system - has been defined and decided. Once performed, validated data and products have to be disseminated. As stated above, such is the role of the EOSDIS system. Data flow via the Tracking and Data Relay Satellite System (TDRSS) to the ground terminals in White Sands, New Mexico. They are then forwarded to GSFC were they undergo Level 0 processing. These data are then transferred to the appropriate Distributed Active Archive Center (DAAC) for further processing (ASTER data are sent to the ASTER Ground Data System (GDS) in Tokyo ; level 1 data are then be forwarded to the EROS Data Center -EDC). Eight DAACs carry out the responsibilities for processing, archiving and distributing EOS and related data on a wide range of uniform supports.
There is little doubt that the EOS system and the TERRA data and products will be a very useful and powerful tool for the global change research works of the MEDIAS network scientists.
