Mission Elements

	ASTER
	CERES
	MISR
	MODIS
	MOPITT

Overview
The Terra platform will fly in a near-polar, sun-synchronous orbit so that it descends across the equator at 10:30 a.m. when daily cloud cover over the land is minimal. It will be followed by its PM counterpart in the year 2000; however, Aqua (EOS PM-1) will fly in an ascending orbit with a 1:30 p.m. equatorial crossing time to represent the diurnal variability.

Terra is designed to house five instruments for simultaneous geolocated measurements and for intercomparison of the new measurement techniques. For example, MODIS' detailed internal calibrations will be used, through simultaneous geolocated measurements, to help in the calibration of ASTER. The MODIS and ASTER high-resolution multi-channel observations of clouds will be used by CERES' low-resolution radiative flux measurements, and by MOPITT to determine the location of clouds as well as their distribution and properties. MISR's multi-angle measurements will determine the angular reflectance properties of land surface features, aerosols, and clouds, all of which will be used by the MODIS, ASTER, and CERES Teams in their data analyses.

Since Terra is a research facility, some of the geophysical products will be derived using more than one instrument and more than one pathway, each with a different set of assumptions and different properties of the product. For example, aerosol properties will be measured by MODIS using its wide spectral range and 1-2 day single view coverage, and also independently by MISR using its multi-angle data, narrower spectral range, and 2-9 day coverage. Vegetation properties will be derived from both MODIS and MISR data. Water vapor will be derived independently from MODIS measurements of reflected near infrared sunlight and emitted terrestrial infrared radiation. The simultaneously geolocated products will allow the EOS instrument teams to develop broad science approaches to specific problems. For instance, in the case of deforestation resulting from biomass burning, fires and emitted smoke particles will be observed by MISR and MODIS, deforestation and burn scars will be observed by ASTER and MODIS, emitted trace gases—carbon monoxide and methane—will be measured by MOPITT, and the radiative forcing of climate will be observed by CERES.

Each instrument was developed under the supervision of a science team that also developed algorithms for analysis of the data and derivation of Earth system measurements. The science teams also will validate these products and use them in their respective scientific investigations.