A series of U. S. Satellites designed for remote sensing and mapping of land areas. These satellites are launched into sun-synchronous orbits that return to image the same swath, two degrees wide, every 16 days. The primary imaging instrument on the first generation of Landsat satellites was a multispectral scanner, a four-channel radiometer with a ground resolution of 80 meters. Landsat-4 and -5 added a second imaging instrument, a thematic mapper, a seven- channel instrument with a ground resolution of 30 meters, used to study vegetation, geology, and other surface features. Landsat-1 (originally called ERTS) was launched in 1972, with Landsat-2 and -3 following in 1975 and 1978. Landsat-4 and -5 were launched in 1982 and 1984.