Envisat – Europe’s gigantic eye on the Earth
ESA satellites have been studying Earth since the 1970s. The most important of these was Envisat, the largest Earth observation spacecraft ever built. Launched by a European Ariane 5 rocket on 1 March 2002, the orbiter spent 10 years circling the planet in a near-polar orbit at an altitude of about 800 km.
Similar in size to double decker bus, the 8,100 kg observatory carried 10 advanced optical and radar instruments. These were used for continuous observation and monitoring of Earth’s land, atmosphere, oceans and ice caps. This scientific payload – the most varied and powerful ever flown on an Earth-sensing satellite - provided a wealth of information on the workings of our world, including insights into factors that affect climate change.
Its largest instrument was a radar which collected echoes from the ground and could take day-night, all-weather images of land and sea surfaces. It could even measure small changes in ground level caused by earthquakes, subsidence or underground volcanic activity.
Other instruments studied tiny plant and animal life in the sea, detected polluting gases in the atmosphere and oil slicks in the ocean, and measured changes in sea ice and global ocean circulation. Envisat also observed the gradual shrinking of Arctic sea ice and the regular opening of the polar shipping routes during summer months. Together with other satellites, it monitored changes in global sea level, as well as global sea-surface temperatures with a precision of a few tenths of a degree. Envisat also studied variations in the ozone hole above Antarctica.
In April 2012, contact with Envisat was suddenly lost and the mission came to an end. However, it prepared the way for ESA’s new series of Sentinel missions. The first of these is expected to be launched in 2014.