Envisat (Environmental Satellite) is an Earth-observing satellite built by the European Space Agency. It was launched on the 1st March 2002 aboard an Ariane 5 into a Sun synchronous polar orbit at a height of 790 km (±10 km). It orbits the Earth in about 101 minutes with a repeat cycle of 35 days. It is the largest European satellite to date (late 2006), with total mass 8211 kg.
Envisat carries an array of nine Earth-observation instruments that gather information about the earth (land, water, ice, and atmosphere) using a variety of measurement principles.
Several of the instruments are advanced versions of instruments that were flown on the earlier ERS-1 and ERS-2 missions and other satellites.
- ASAR (Advanced Synthetic Aperture Radar) operating in C band can detect changes in surface heights with sub-millimeter precision.
- MERIS (MEdium Resolution Imaging Spectrometer) measures the reflectance of the Earth (surface and atmosphere) in the solar spectral range (390 to 1040 nm) and transmits 15 spectral bands back to the ground segment.
- AATSR (Advanced Along Track Scanning Radiometer) can measure the temperature of the sea surface
- RA-2 (Radar Altimeter 2) is a dual-frequency Nadir pointing Radar operating in the Ku band and S bands, it is used to define ocean topography, map/monitor sea ice and measure land heights.
- MWR (Microwave Radiometer) for measuring water vapour in the atmosphere and estimate the tropospheric delay for the Altimeter
- DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) for orbit determination to within 10 cm or less
- GOMOS (Global Ozone Monitoring by Occultation of Stars) looks to stars as they descend through the Earth's atmosphere and change color, which also tells a lot about the presence of gases such as O3 (ozone), and allows for the first time a space-based measurement of the vertical distribution of these trace gases.
- MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) is a spectrometer
- SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) compares light coming from the sun to light reflected by the Earth, which provides information on the atmosphere through which the earth-reflected light has passed.