LANDSAT satellites were launched into orbit in 1972 and 1975. Additional LANDSAT satellites will be launched in 1978 and 1981. The satellites orbit the Earth every 18 days at an altitude of approximately 900 km. A sun-synchronous orbit is utilized to insure repeatable illumination conditions. Seasonal variations in solar illumination must be analyzed to select the best LANDSAT data for geologic applications. LANDSAT data may be viewed in stereo where there is sufficient sidelap and sufficient topographic relief. Repetitive satellite coverage allows optimal cover conditions for geologic applications to be identified. The present LANDSAT satellites detect only solar radiation that is reflected from the earth's surface in visible and near-visible wavelengths. The third LANDS T satellite will detect emitted thermal radiation. The Multispectral Scanner (MSS) is the only sensing instrument operating on the first two satellites. The MSS on LANDSATS 1 and 2 detects radiation which is reflected from a 79 × 79-m area, and the data are formatted as if the measurement were made from a 56 × 79-m area.

The MSS integrates spectral response from all cover types within the 79 × 79-m area. The integrated spectral signature often does not resemble the spectral signature from individual cover types, and the integrated signature is also modified by the atmosphere. LANDSAT 1 and 2 data are converted to 70-mm film and computer compatible tapes (CCT's) at Goddard Space Flight Center (GSFC) and are shipped to the EROS Data Center (EDC) for distribution to users. LANDSAT-C data will be converted to 241-mm wide film and CCT's at EDC. LANDSAT-D data will be relayed from the satellite collection platform directly to geosynchronous satellites and then to the United States from any location on Earth.

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