How do we observe the Earth?
For many centuries, the only way to obtain a good view of a large area was to climb to higher ground. Then the invention of balloons and aircraft made Earth observation a lot easier.
During the space age, satellites have been used more and more to look at every aspect of our planet.
Since they look at the Earth from a long way away, they are often called “remote sensing” satellites.
The most detailed pictures of the Earth’s surface and atmosphere are sent back by satellites in low orbits that carry them over the north and south poles.
As the Earth turns beneath them, these satellites can image the entire planet – strip by strip – every few days.
Satellites in polar orbits study ice and snow cover, land use, air and water pollution, and local weather. ESA's polar orbiters are the European Remote Sensing Satellite (ERS-2) and the Environmental satellite, Envisat.
Other spacecraft continually stare at the same part of the Earth as they orbit 36,000 km above the equator. This gives them a wider view, but it means they cannot see the Earth in as much detail.
Europe has so far launched eight weather satellites, called Meteosat, into this type of “geostationary” orbit.
Last modified 13 December 2004
