Envisat, A health check for our planet

A health check for our planet

• In operation
• Launched in 2002
• Due extended until 2010

Envisat is Europe’s largest and most sophisticated Earth observation satellite. The spacecraft is around the size of a double-decker bus and has ten instruments on board monitoring everything from air to agriculture, oceans to ozone. Day and night, whatever the weather, Envisat is providing information on the state of the planet we live on.

Operated by the European Space Agency (ESA), Envisat is designed to answer some of the key questions about our environment. Its instruments measure parts of the Earth system - from the oceans and atmosphere to land and areas covered with ice. Over the duration of the mission, Envisat will be able to spot any changes and examine the effect of those changes on the Earth.

Many of Envisat’s instruments are a development of those that flew on ESA’s Earth Observation missions of the 1990s: ERS-1 & -2. This means that scientists now have satellite readings stretching back more than 15 years.

Envisat’s sensors are mapping the world’s oceans to monitor changes in sea level and produce accurate maps of ice coverage. Sea surface temperatures are also being recorded. The distribution of phytoplankton is being observed using the MERIS (Medium Resolution Imaging Spectrometer) imaging instrument. There is now sufficient data from space missions to show long-term trends in sea level rise and reduced sea ice cover in the Arctic.

A key part of the Envisat mission is to investigate the extent and impact of pollution. The suite of sensors on board the spacecraft is able to see the holes in the ozone layer, the plumes of aerosols hanging over major cities or burning forests and the exhaust trails deposited in the high atmosphere by commercial airliners. Over the longer term, Envisat is collecting data to monitor the greenhouse effect so future trends can be predicted.

For the latest news on the mission visit the Envisat website.

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Mission facts

• Envisat is the largest Earth observation spacecraft ever built and had a launch weight of 8.2 tonnes.
  
  
• Envisat was launched on 1 March 2002 from Kourou, French Guiana. Its mission was originally intended to last five years.
  
  
• Envisat flies in a polar orbit, so over a three day period the satellite’s instruments can monitor the entire globe.
  
  
• Envisat data has become increasingly valuable for monitoring disasters such as volcanic eruptions, floods and fires. The satellite was able to monitor smoke from Europe's largest peacetime fire at the Buncefield oil storage depot near London and the floods in northern and south west England in 2007.
  
  
• The satellite has been taking annual measurements of the ozone hole over Antarctica. Any gap in the stratospheric ozone layer leaves us unprotected from harmful UV radiation. In 2007, data from Envisat showed the hole had shrunk by a third compared to the previous year's record size.
  
  
• Envisat’s radar has been used to monitor shifts in the Earth’s crust. Scientists at Oxford University are studying seismic belts across the world in the hope of using Envisat data to help predict future earthquakes.

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Technology

Envisat carries ten instruments to study the air, land and sea. These instruments operate at visible, infrared, ultraviolet and microwave wavelengths.

Advanced Along Track Scanning Radiometer (AATSR) measures surface temperature. It is studying changes that have taken place in sea surface temperature over a decade.

Advanced Synthetic Aperture Radar (ASAR) is the largest of Envisat's instruments. ASAR bounces microwave signals off Earth's surface to monitor any shifts in the Earth’s crust. It is also used to study ocean waves and monitor deforestation.

Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument provides valuable information about the Earth’s ozone layer.

Medium Resolution Imaging Spectrometer (MERIS) measures solar radiation reflected by the Earth's surface and clouds. MERIS is used to monitor coastal pollution and chlorophyll levels in water by studying ocean colour.

Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) keeps track of air pressure and ozone concentration.

MicroWave Radiometer (MWR) measures the amount of atmospheric water vapour and liquid water in clouds.

Radar Altimeter- 2 (RA-2) measures the height of water in the world's oceans as well as looking at wind speed.

Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) provides measurements of trace gases, aerosols and cloud height in the atmosphere. This is vital for measuring emissions of greenhouse gases and industrial pollutants.

Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) pinpoints Envisat's orbital location. This data is used to help monitor glaciers, landslides and volcanoes.

UK involvement

From conception to design, building and operation of Envisat, UK scientists and industry partners have been at the forefront of the satellite's progress.

Many UK teams are involved in collecting and analysing results from Envisat with more than 1,200 scientific projects across Europe currently using data from this mission.

UK science groups include:

• UK Natural Environment Research Council (NERC)
• Data Assimilation Research Centre at the University of Reading (DARC)
• University of Leicester
• Oxford University
• STFC Rutherford Appleton Laboratory (RAL)

Astrium Limited was the prime contractor for the satellite platform.

BAE Systems developed the eight infrared detectors and pre-amplifiers for the MIPAS instrument.

COM DEV Europe Limited produced the pre-amplifier warm unit for MIPAS. This unit takes output from infrared detectors and amplifies this for the data processing unit.

Infoterra (part of EADS Astrium) developed the archive facility and is overseeing the running of the UK data processing and archive centre.

LogicaCMG was the prime contractor for designing the ground segment for Phase-B studies. Logica has also been working under contract to Astrium Limited to develop on board software for the satellite.

QinetiQ has represented BNSC on the European Space Agency Data Operations Science and Technology Advisory Group.

Sira Electro-Optics Limited was responsible for much of the ozone monitoring software on GOMOS. Additionally, Sira played a leading role in the development of MERIS (the solar radiation measuring instrument).

VEGA was involved in five areas: technical management support for AATSR; engineer provision for the integration and testing of Envisat's science payload; supporting the Envisat Systems Engineering team; working with German staff to operate the satellite once in orbit; and producing the Enviview CD-ROM software package for reading, viewing and reformatting data from Envisat instruments.