Since its creation in 1958, NASA has been studying the Earth and its changing environment by observing the atmosphere, oceans, land, ice and snow, their influence on climate and weather. In 1991, NASA launched a comprehensive program to study the Earth as an environmental system called the Earth Science Enterprise which comprised of focused, free-flying satellites, space shuttle missions, and various air-borne and ground based studies. Phase-II began in 1999 with the launch of the first EOS satellite, TERRA (formerly AM-1) and Landsat-7. The AM satellite orbits in sun synchronous polar orbit, descending southward and crosses equator in the morning. The other satellite is AQUA (PM - I). This also orbits in sun synchronous polar orbit, ascending northward in the afternoon. NRSC has been acquiring and disseminating TERRA-MODIS data since November 2002. From January 2004 onwards, NRSC is acquiring data from AQUA satellite also. The TERRA and AQUA satellites carry a number instruments out of which NRSC acquires data collected by the Moderate Resolution Imaging Spectro Radiometer (MODIS ) sensor alone.
Moderate Resolution Imaging Spectro Radiometer (MODIS) - Moderate Resolution Imaging Spectro Radiometer (MODIS) is the key instrument in EOS Satellites. It is a passive imaging spectro radiometer. It scans across-track, a swath of 2330 km using 36 discrete spectral bands (visible, near and thermal infra red) between 0.41 and 14.2 micrometers. It provides imagery of the earth's surface and cloud cover to develop an improved understanding of global dynamics and processes occurring on the surface and in the lower atmosphere. Some of the channels are available at different resolutions (1 and 2 at 250m, 3-7 at 500m). MODIS data comes in Hierarchical Data Format file which enables storing of multi type data sets. The HDF file for the lower resolution data contains the higher resolution data down sampled to the lower resolution. While the equatorial crossing time of TERRA is 10:30 A.M., the same for AQUA is 1:30 P.M. AQUA's afternoon crossing time was chosen for its usefulness for meteorological forecasting.
More mission details at MODIS Web site
