Earth observation satellites
Six Earth observation satellites comprising the A-train
satellite constellation as of 2014.
or Earth remote sensing satellites
specifically designed for Earth observation
, similar to spy satellites
but intended for non-military uses such as environmental
, map making
The first occurrence of satellite remote sensing can be dated to the launch of the first artificial satellite, Sputnik 1
, by the Soviet Union on October 4, 1957. Sputnik 1 sent back radio signals, which scientists used to study the ionosphere
NASA launched the first American satellite, Explorer 1
, in January 31, 1958. The information sent back from its radiation detector led to the discovery of the Earth's Van Allen radiation belts
spacecraft, launched on April 1, 1960 as part of NASA's TIROS
(Television Infrared Observation Satellite) Program, sent back the first television footage of weather patterns to be taken from space.
, more than 150 Earth observation satellites were in orbit, recording data with both passive and active sensors and acquiring more than 10 terabits of data daily.
Most Earth observation satellites carry instruments that should be operated at a relatively low altitude. Altitudes below 500-600 kilometers are in general avoided, though, because of the significant air-drag
at such low altitudes making frequent orbit reboost
maneuvres necessary. The Earth observation satellites ERS-1, ERS-2
of European Space Agency
as well as the MetOp
spacecraft of EUMETSAT
are all operated at altitudes of about 800 km. The Proba-1
spacecraft of European Space Agency are observing the Earth from an altitude of about 700 km. The Earth observation satellites of UAE, DubaiSat-1
are also placed in Low Earth Orbits (LEO)
orbits and providing satellite imagery
of various parts of the Earth. Read more...