A story of the Landsat program
The Landsats have an interesting political and technological story reaching back decades; click here to read author Stephen Hall's version of that story.
Brief facts of the Landsat program
In the mid-1960s the Department of the Interior conceived the concept of an Earth-monitoring satellite for resource managers and Earth scientists. The National Aeronautics and Space Administration (NASA) joined the initiative, and in the early 1970s NASA and the U.S. Geological Survey entered into a partnership, with NASA operating the Landsats and the U.S. Geological Survey handling the data. In the early 1980s operations transferred from NASA to the National Oceanic and Atmospheric Administration (NOAA), in the Department of Commerce. In October 1985, the Landsat system was commercialized, and the Earth Observation Satellite Company (EOSAT) assumed responsibility for its operation.
Throughout these changes, the USGS Earth Resources Observation and Science Center (EROS) retained primary responsibility as the government archive of data from the Landsats. This responsibility was formalized in the Land Remote Sensing Policy Act of 1992 (Public Law 102-555), which officially authorized a National Satellite Land Remote Sensing Data Archive. This archive is at EROS.
The Landsat program is the longest-running program of remote sensing from space. Landsat 1, originally known as the Earth Resources Technology Satellite (ERTS), was launched on 23 July 1972. It functioned well beyond its designated life expectancy of one year, finally ceasing to operate on 6 January 1978, more than five years after its launch date. By that time Landsat 3 was about to be launched; between 1972 and 1984 a Landsat was launched roughly every three years (Landsats 1-5). Landsats 1-3 carried the Multispectral Scanner (MSS) and three return-beam vidicons (RBVs), which were more like TV cameras and which were used little. Landsats 4 and 5 were virtually identical; each carried an MSS sensor and an improved scanner, the Thematic Mapper (TM), which has more bands and finer resolution than the MSS sensor. Landsat 6 was launched on 5 October 1993, but failed to achieve orbit. Landsat 6 was equipped with the enhanced Thematic Mapper (ETM). Landsat 7 was launched on 15 April 1999, and carries the ETM+ sensor, great-grandchild of the MSS and a further improvement on the ETM.
Landsat satellites, 1972-2003
Launch Decommission Alt. Angle Revisit Sensors Data rate
--------------------------------------------------------------------------
1 23 Jul 1972 6 Jan 1978 917 km 99.6 18 days MSS, RBV 15 Mbps
2 22 Jan 1975 25 Feb 1982 917 km 99.2 18 days MSS, RBV 15 Mbps
3 5 Mar 1978 31 Mar 1983 917 km 99.1 18 days MSS, RBV 15 Mbps
4 16 Jul 1982 * Aug 1993 705 km 98.9 16 days MSS, TM 85 Mbps
5 1 Mar 1984 705 km 98.9 16 days MSS, TM 85 Mbps
6 5 Oct 1993 ** Oct 1993 (705 km) (16 days) (ETM) (85 Mbps)
7 15 Apr 1999 *** 705 km 98.2 16 days ETM+ 150 Mbps
1972 1980 1990 2000
| . . | . . . . | . . . . | . . . . | . . . . | . . . . | . . .
Landsat 1 -----------
Landsat 2 ---------------
Landsat 3 -----------
Landsat 4 ----------------------
Landsat 5 -------------------------------------->
Landsat 6 -
Landsat 7 -------->
* Landsat 4's data transmission stopped in August 1993.
** Landsat 6 crashed at launch.
*** Landsat 7's scan line corrector failed on 31 May 2003.
The orbits of these satellites are different from those of the communication satellites at which we point television dishes. These communication satellites are geosynchronous, meaning they orbit at the same speed the Earth rotates, so that each satellite remains above a certain spot on the equator. Contrast this to Landsat 5, for example. It orbits the Earth almost perpendicular to the equator (i.e. almost from pole to pole). Because the Earth is spinning below it, the satellite can eventually take pictures of the entire surface of the planet. This is called a sun-synchronous orbit, because whenever Landsat 5 passes over Quito, for example, the satellite, sun, and city are always in the same geometric relationship to each other. In other words, if you gauge the time of day by the Sun only and disregard time zones etc., whenever Landsat 5 passes over Quito it is about 9:45 a.m. If this were not so, it would be difficult to compare images as we do in Earthshots. In fact, whenever Landsat 5 passes over the equator (in its daytime, descending, north-to-south pass) it is about 9:45 a.m. in "Sun time."
(If it helps you, stand up, walk south-southwest, look down, and "scan" your eyes left and right. There-- your head is a Landsat. Pretend it is midmorning, and think about where the Sun is in relation to your head. That will depend on your latitude, but in any case the Sun should be somewhere to your left (and above you). Or, you can download a satellite-tracking program and watch the Sun and satellites on your screen.
Landsat 7 orbits the Earth every 99 minutes or so, or about 14 times every 24 hours. It takes 16 days for it to "see" the entire Earth (except the very poles, over which it never passes) in the daytime. Landsat 7 sees "swaths" of the Earth 185 km wide. There is overlap between these swaths; at the equator, for example, the east 7% and west 7% of a scene is duplicated by the neighboring scenes, and this amount increases to about 85% at the satellite's maximum latitude of 81 degrees north and south. Half of the time a Landsat "ascends" northward in the dark, and half of the time it "descends" southward in midmorning sunlight, scanning the Earth for reflected and emitted electromagnetic radiation (EMR).
(See the next help article to see areas covered by the Landsat archives.)
How to cite this article
Campbell, Robert Wellman, ed. 2008. "Help: The Landsat program." Earthshots: Satellite Images of Environmental Change. U.S. Geological Survey. http://earthshots.usgs.gov. This article was first released 1 January 1998, and last revised 14 August 2008.