Eyes in the sky

The Landsat remote-sensing program, begun in 1972 with the launch of Landsat 1, has provided continuous images of large portions of the Earth's surface, enabling researchers to see how nature and human activity have changed the face of the planet over time.

Data from Landsat sensors is sent to ground receiving stations in the United States and abroad and eventually stored in databases at the U.S. Geological Survey's Earth Resources Observation Systems Data Center in Sioux Falls, S.D. Seven Landsats have been launched, although Landsat 6 did not achieve orbit.

Only two Landsats are still capable of collecting and transmitting data: the soon-to-be-decommissioned Landsat 5, launched in 1984, and Landsat 7, launched in 1999 and designed to be operational for at least five years.