The Pearl River Delta from Space
More on the statellites
Corona, USA's first operational intelligence satellite, carried sophisticated optical cameras (KH-4B system) to acquire imagery of the Earth from space at an altitude of 80 nautical miles (150 km). It was launched in 1967. The camera system included two 24-inch focal length, f3.5 panoramic cameras with separate forward looking and rear looking capability, and a tilting angle of 30 degrees to take stereoscopic photos. Films taken by the camera were contained in a capsule. The satellite was designed to de-orbit the film capsules from space, which were recovered in mid-air by specially equipped aircraft.
Landsat was called ERTS (Earth Resources Technology Satellites) when it was first launched in 1972. This series of satellites was renamed Landsat in 1995. Administered by USGS/NASA, Lansat-5 acquired only colour images of 30-metre resolution. Landsat-7, which launched on April 15, 1999, is orbiting the Earth at an altitude of 705 km. It acquires black and white images with a resolution of 15-metre and colour images with a resolution of 30-metre.