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Envisat

From Alfawiki
Envisat
Company typeSatellite mission
IndustryEarth observation
FoundedMarch 1, 2002; 24 years ago (2002-03-01)
FounderEuropean Space Agency (ESA)
DefunctMay 9, 2012 (2012-05-09)
FateMission concluded, satellite remains as space debris
Headquarters
Kourou (launch site)
,
French Guiana
Area served
Global Earth observation
ProductsEarth observation data for atmospheric, oceanic, terrestrial, and cryospheric monitoring
OwnerEuropean Space Agency (ESA)
Websitewww.esa.int/Applications/Observing_the_Earth/Envisat

Envisat (short for Environmental Satellite) represented the largest civilian Earth observation satellite globally and was managed by the European Space Agency (ESA). It was launched on 1 March 2002 via an Ariane 5 rocket from the Guyana Space Centre located in Kourou. The satellite entered a Sun-synchronous polar orbit approximately 790 ± 10 km above Earth, completing a full orbit every 101 minutes and repeating its ground track every 35 days.

Contact with Envisat was lost on 8 April 2012, leading ESA to officially conclude the mission on 9 May 2012. The satellite, which cost €2.3 billion including five years of operational expenses, remains in orbit as space debris. Its operational role has been taken over by the Sentinel family, with Sentinel 1 assuming Envisat’s radar observation responsibilities after its launch in 2014.

Mission

Envisat was deployed as an Earth observation satellite to extend the legacy of the European Remote-Sensing Satellite missions, focusing on enhanced environmental surveillance. The data it collected supported a wide array of scientific disciplines such as atmospheric chemistry, investigations into ozone depletion, measurements of ocean temperature and colour, hydrology including humidity and flood monitoring, agricultural assessment, natural disaster analysis, maritime traffic oversight, pollution tracking, cartography, as well as studies of snow and ice.

Specifications

Dimensions

The satellite measured × × once in orbit with solar panels fully extended.

Mass

It had a launch mass of , which included of propellant and an instrument payload weighing .

Power

The solar arrays generated a power output of 3560 W.

Instruments

Envisat was equipped with nine instruments dedicated to Earth observation covering terrestrial, aquatic, cryospheric, and atmospheric parameters. Additionally, a tenth instrument named DORIS was used for navigation and attitude control. Many sensors were enhanced iterations derived from those flown on previous missions like ERS-1 and ERS 2.

MWR

The MWR (Microwave Radiometer) instrument was designed to measure atmospheric water vapour content.

AATSR

AATSR (Advanced Along Track Scanning Radiometer) monitored sea surface temperatures across visible and infrared wavelengths with an accuracy of , supporting climate studies. It also gathered data on environmental factors such as moisture levels, vegetation biomass, and plant health.

MIPAS

MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) functioned as a Fourier-transform infrared spectrometer that provided vertical profiles of pressure and temperature along with concentrations of trace gases including nitrogen dioxide, nitrous oxide, methane, nitric acid, ozone, and water vapour within the stratosphere. It operated year-round under both day and night conditions with high spectral resolution and vertical resolution varying according to altitude.

MERIS

MERIS (Medium Resolution Imaging Spectrometer) captured reflectance data from Earth's surface and atmosphere in the solar spectral range between 390 and 1040 nm, transmitting information in 15 spectral bands to ground stations. This instrument was developed at the Cannes Mandelieu Space Center.

SCIAMACHY

SCIAMACHY (Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY) analyzed sunlight compared to Earth-reflected radiation to map trace gases and aerosols across the troposphere and stratosphere. It recorded high-resolution spectra ranging from 0.2 to 0.5 nm across wavelengths between 240 and 1700 nm, partially extending up to 2400 nm. This capability allowed detection of trace gases, aerosols, and cloud formations. SCIAMACHY operated in three distinct modes: nadir viewing, limb scanning, and during solar or lunar eclipses. Its development was a collaborative effort between the Netherlands and Germany involving TNO/TPD, SRON, and Airbus Defence and Space Netherlands.

RA-2

RA-2 (Radar Altimeter 2) is a dual-frequency radar instrument oriented nadir, functioning in both Ku and S bands. It provides measurements of ocean surface topography, tracks sea ice conditions, and evaluates terrestrial elevations. Continuous mean sea level datasets from Envisat are accessible through the Centre National d'Etudes Spatiales.

ASAR

ASAR (Advanced Synthetic Aperture Radar) operates within the C band and supports multiple operational modes, capable of detecting surface height variations with sub-millimeter accuracy. It was utilized during the ERS-1 and ERS-2 missions, facilitating observations across various polarizations, incidence angles, and spatial resolutions.

Mode Id Polarisation Incidence Resolution Swath
Alternating polarisation AP HH/VV, HH/HV, VV/VH 15–45° 30–150 m 58–110 km
Image IM HH, VV 15–45° 30–150 m 58–110 km
Wave WV HH, VV 400 m 5 km × 5 km
Suivi global (ScanSAR) GM HH, VV 1000 m 405 km
Wide Swath (ScanSAR) WS HH, VV 150 m 405 km

ASAR data products are categorized as follows:

  • RAW (Level 0): unprocessed data intended for image generation.
  • S (Single Look Complex): complex-valued imagery.
  • P (Precision Image): enhanced images with uniform pixel spacing (12.5 m for IMP).
  • M (Medium Precision): radiometrically enhanced images with lower resolution than P.
  • G (Geocoded): images corrected for basic geographic positioning.

The WV mode captures discrete scenes measuring 5 km × 5 km at intervals of approximately 100 km.

DORIS

DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) provides satellite orbit determination with an accuracy of .

GOMOS

GOMOS (Global Ozone Monitoring by Occultation of Stars) analyzes starlight passing through Earth's atmosphere to quantify atmospheric constituents such as ozone (). It detects trace gases including nitrogen dioxide (), nitrogen trioxide (), , ozone, and aerosols within altitudes ranging from , achieving a resolution of .

Loss of contact

On 12 April 2012, ESA announced that contact with Envisat had been lost on 8 April 2012 after a decade in operation—surpassing its designed lifespan by five years. Despite remaining in a stable orbit, all communication attempts were unsuccessful. To evaluate the satellite’s condition, ground-based radar and the French Pleiades Earth observation satellite captured images of Envisat. ESA officially declared the mission concluded on 9 May 2012. Launched in 2002, Envisat exceeded its expected operational duration by five years and delivered over one petabyte of data. The original plan was to deactivate the satellite in 2014.

Space safety

Envisat represents a long-term collision hazard due to space debris accumulation. Its orbital characteristics and area-to-mass ratio imply it will require roughly 150 years to naturally re-enter Earth's atmosphere. Each year, two catalogued debris objects pass within about of Envisat's position, likely necessitating avoidance maneuvers. Even an impact with debris as small as 10 kg could produce significant fragmentation, potentially initiating a debris cascade known as the Kessler Syndrome.

Envisat was identified as a target for ESA’s proposed e.Deorbit mission focused on active space debris removal; the servicing spacecraft designed for this operation would have an approximate mass of 1.6 tonnes.

See also

External links

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