Envisat ("Environmental Satellite") is a large Earth-observing satellite which has been inactive since 2012. It is still in orbit and considered space debris. Operated by the

European Space Agency The European Space Agency (ESA) is a 23-member International organization, international organization devoted to space exploration. With its headquarters in Paris and a staff of around 2,547 people globally as of 2023, ESA was founded in 1975 ...

(ESA), it was the world's largest civilian Earth observation satellite. It was launched on 1 March 2002 aboard an

Ariane 5 Ariane 5 is a retired European heavy-lift space launch vehicle operated by Arianespace for the European Space Agency (ESA). It was launched from the Guiana Space Centre (CSG) in French Guiana. It was used to deliver payloads into geostationar ...

from the Guyana Space Centre in Kourou,

French Guiana French Guiana, or Guyane in French, is an Overseas departments and regions of France, overseas department and region of France located on the northern coast of South America in the Guianas and the West Indies. Bordered by Suriname to the west ...

, into a Sun synchronous

polar orbit A polar orbit is one in which a satellite passes above or nearly above both poles of the body being orbited (usually a planet such as the Earth, but possibly another body such as the Moon or Sun) on each revolution. It has an inclination of abo ...

at an altitude of 790 ± 10 km. It

orbit In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an ...

s the

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

in about 101 minutes, with a repeat cycle of 35 days. After losing contact with the satellite on 8 April 2012, ESA formally announced the end of Envisat's mission on 9 May 2012. Envisat cost 2.3 billion Euro (including 300 million Euro for 5 years of operations) to develop and launch. The mission has been replaced by the

Sentinel Sentinel may refer to: Places Mountains * Mount Sentinel, a mountain next to the University of Montana in Missoula, Montana * Sentinel Buttress, a volcanic crag on James Ross Island, Antarctica * Sentinel Dome, a naturally occurring granit ...

series of satellites. The first of these, Sentinel 1, has taken over the radar duties of Envisat since its launch in 2014.

Mission

Envisat was launched as an

Earth observation satellite An Earth observation satellite or Earth remote sensing satellite is a satellite used or designed for Earth observation (EO) from orbit, including spy satellites and similar ones intended for non-military uses such as environmental monitoring, me ...

. Its objective was to support the continuity of European Remote-Sensing Satellite missions, providing additional observations to improve environmental studies. To accomplish the global and regional objectives of the mission, numerous scientific disciplines used the data acquired from the sensors on the satellite to study

atmospheric chemistry Atmospheric chemistry is a branch of atmospheric science that studies the chemistry of the Earth's atmosphere and that of other planets. This multidisciplinary approach of research draws on environmental chemistry, physics, meteorology, comput ...

ozone depletion Ozone depletion consists of two related events observed since the late 1970s: a lowered total amount of ozone in Earth, Earth's upper atmosphere, and a much larger springtime decrease in stratospheric ozone (the ozone layer) around Earth's polar ...

biological oceanography Biological oceanography is the study of how organisms affect and are affected by the physics, chemistry, and geology of the oceanographic system. Biological oceanography may also be referred to as ocean ecology, in which the root word of ecology ...

, ocean temperature and colour, wind waves,

hydrology Hydrology () is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and drainage basin sustainability. A practitioner of hydrology is called a hydro ...

(

humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation (meteorology), precipitation, dew, or fog t ...

flood A flood is an overflow of water (list of non-water floods, or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are of significant con ...

s), agriculture and

arboriculture Arboriculture (, from ) is the cultivation, management, and study of individual trees, shrubs, vines, and other perennial woody plants. The science of arboriculture studies how these plants grow and respond to cultural practices and to their env ...

, natural hazards,

digital elevation model A digital elevation model (DEM) or digital surface model (DSM) is a 3D computer graphics representation of elevation data to represent terrain or overlaying objects, commonly of a planet, Natural satellite, moon, or asteroid. A "global DEM" refer ...

ling (using

interferometry Interferometry is a technique which uses the ''interference (wave propagation), interference'' of Superposition principle, superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important inves ...

), monitoring of maritime traffic, atmospheric dispersion modelling (pollution),

cartography Cartography (; from , 'papyrus, sheet of paper, map'; and , 'write') is the study and practice of making and using maps. Combining science, aesthetics and technique, cartography builds on the premise that reality (or an imagined reality) can ...

and

snow Snow consists of individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water througho ...

and

ice Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 ° C, 32 ° F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally oc ...

Specifications

;Dimensions × × in orbit with the solar array deployed. ;Mass , including of fuel and a instrument payload. ;Power Solar array with a total load of 3560 W.

Instruments

Envisat carries an array of nine Earth-observation instruments that gathered information about the Earth (land,

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

, and

atmosphere An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

) using a variety of measurement principles. A tenth instrument, DORIS, provided guidance and control. Several of the instruments were advanced versions of instruments that were flown on the earlier ERS-1 and ERS 2 missions and other satellites.

MWR

MWR (

Microwave Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequency, frequencies between 300&n ...

Radiometer) was designed for measuring

water vapour Water vapor, water vapour, or aqueous vapor is the gaseous phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Water vapor ...

in the

AATSR

AATSR (Advanced Along Track Scanning

Radiometer A radiometer or roentgenometer is a device for measuring the radiant flux (power) of electromagnetic radiation. Generally, a radiometer is an infrared radiation detector or an ultraviolet detector. Microwave radiometers operate in the micro ...

) can measure the

sea A sea is a large body of salt water. There are particular seas and the sea. The sea commonly refers to the ocean, the interconnected body of seawaters that spans most of Earth. Particular seas are either marginal seas, second-order section ...

surface temperature in the visible and infrared spectra. It is the successor of ATSR1 and ATSR2, payloads of ERS 1 and ERS 2. AATSR can measure Earth's surface temperature to a precision of , for climate research. Among the secondary objectives of AATSR is the observation of environmental parameters such as water content, biomass, and vegetal health and growth.

MIPAS

MIPAS (Michelson

Interferometer Interferometry is a technique which uses the '' interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber opt ...

for Passive Atmospheric Sounding) is a

Fourier transform In mathematics, the Fourier transform (FT) is an integral transform that takes a function as input then outputs another function that describes the extent to which various frequencies are present in the original function. The output of the tr ...

ing infrared spectrometer which provides pressure and temperature profiles, and profiles of trace gases nitrogen dioxide (),

nitrous oxide Nitrous oxide (dinitrogen oxide or dinitrogen monoxide), commonly known as laughing gas, nitrous, or factitious air, among others, is a chemical compound, an Nitrogen oxide, oxide of nitrogen with the Chemical formula, formula . At room te ...

(), methane (), nitric acid (), ozone (), and water () in the

stratosphere The stratosphere () is the second-lowest layer of the atmosphere of Earth, located above the troposphere and below the mesosphere. The stratosphere is composed of stratified temperature zones, with the warmer layers of air located higher ...

. The instrument functions with high spectral resolution in an extended spectral band, which allows coverage across the Earth in all seasons and at equal quality night and day. MIPAS has a vertical resolution of depending on altitude (the larger at the level of the upper stratosphere).

MERIS

MERIS (MEdium Resolution Imaging

Spectrometer A spectrometer () is a scientific instrument used to separate and measure Spectrum, spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomeno ...

) 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 A ground segment consists of all the ground-based elements of a spaceflight, space system used by operators and support personnel, as opposed to the Satellite space segment, space segment and user segment. The ground segment enables management of ...

. MERIS was built at the Cannes Mandelieu Space Center.

SCIAMACHY

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. SCIAMACHY is an image spectrometer with the principal objective of mapping the concentration of trace gases and aerosols in the troposphere and stratosphere. Rays of sunlight that are reflected transmitted, backscattered and reflected by the atmosphere are captured at a high spectral resolution (0.2 to 0.5 nm) for wavelengths between 240 and 1700 nm, and in certain spectra between 2,000 and 2,400 nm. Its high spectral resolution over a wide range of wavelengths can detect many trace gases even in tiny concentrations. The wavelengths captured also allow effective detection of aerosols and clouds. SCIAMACHY uses 3 different targeting modes: to the nadir (against the sun), to the limbus (through the atmospheric corona), and during solar or lunar eclipses. SCIAMACHY was built by Netherlands and Germany at TNO/TPD, SRON and Airbus Defence and Space Netherlands.

RA-2

RA-2 (

Radar Radar is a system that uses radio waves to determine the distance ('' ranging''), direction ( azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track ...

Altimeter An altimeter or an altitude meter is an instrument used to measure the altitude of an object above a fixed level. The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth under water. Ty ...

2) is a dual-

frequency Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...

Nadir The nadir is the direction pointing directly ''below'' a particular location; that is, it is one of two vertical directions at a specified location, orthogonal to a horizontal flat surface. The direction opposite of the nadir is the zenith. Et ...

pointing Radar operating in the K_u band and

S band The S band is a designation by the Institute of Electrical and Electronics Engineers (IEEE) for a part of the microwave band of the electromagnetic spectrum covering frequencies from 2 to 4 gigahertz (GHz). Thus it crosses the conventiona ...

s, it is used to define

ocean The ocean is the body of salt water that covers approximately 70.8% of Earth. The ocean is conventionally divided into large bodies of water, which are also referred to as ''oceans'' (the Pacific, Atlantic, Indian Ocean, Indian, Southern Ocean ...

topography Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the landforms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary sci ...

, map/monitor

sea ice Sea ice arises as seawater freezes. Because ice is less density, dense than water, it floats on the ocean's surface (as does fresh water ice). Sea ice covers about 7% of the Earth's surface and about 12% of the world's oceans. Much of the world' ...

and measure land heights. Mean sea level measurements from Envisat are continuously graphed at the Centre National d'Etudes Spatiales web site, on the Aviso page.

ASAR

ASAR (Advanced Synthetic Aperture Radar) operates in the C band in a wide variety of modes. It can detect changes in surface heights with sub-

millimeter 330px, Different lengths as in respect of the electromagnetic spectrum, measured by the metre and its derived scales. The microwave is between 1 metre to 1 millimetre. The millimetre (American and British English spelling differences#-re, -er, i ...

precision. It served as a data link for ERS 1 and ERS 2, providing numerous functions such as observations of different polarities of light or combining different polarities, angles of incidence and spatial resolutions. These different types of raw data can be given several levels of treatment (suffixed to the ID of the acquisition mode: IMP, APS, and so on): * RAW (raw data, or "Level 0"), which contains all the information necessary to create images. * S (complex data, "Single Look Complex"), images in complex numeric form, the real and imaginary parts of the output of the compression algorithm * P (precision image), amplified image with constant pixel width (12.5 m for IMP) * M (medium precision image), amplified radiometry image with a resolution greater than P * G (geocoded image), amplified image to which simple geographical transforms have been applied to show relief. Data capture in WV mode is unusual in that they constitute a series of 5 km × 5 km spaced at 100 km.

DORIS

DORIS ( Doppler Orbitography and Radiopositioning Integrated by Satellite) determines the satellite's orbit to within .

GOMOS

GOMOS (Global

Ozone Ozone () (or trioxygen) is an Inorganic compound, inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , break ...

Monitoring by Occultation of

Star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

s) looks at stars as they descend through the Earth's atmosphere and change colour, allowing measurement of gases such as ozone (), including their vertical distribution. GOMOS uses the principle of

occultation An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks f ...

. Its sensors detect light from a star traversing the Earth's atmosphere and measures the depletion of that light by trace gases nitrogen dioxide (), nitrogen trioxide, (), ), ozone () and aerosols present between about altitude. It has a resolution of .

End of mission

Loss of contact

ESA announced on 12 April 2012 that they lost contact with Envisat on Sunday, 8 April 2012, after 10 years of service, exceeding the initially planned life span by 5 years. The spacecraft was still in a stable orbit, but attempts to contact it were unsuccessful. Ground-based radar and the French

Pleiades The Pleiades (), also known as Seven Sisters and Messier 45 (M45), is an Asterism (astronomy), asterism of an open cluster, open star cluster containing young Stellar classification#Class B, B-type stars in the northwest of the constellation Tau ...

Earth probe were used to image the silent Envisat and look for damage. ESA formally announced the end of Envisat's mission on 9 May 2012. Envisat was launched in 2002 and it operated five years beyond its planned mission lifetime, delivering over a

petabyte The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable un ...

of data. ESA was expecting to turn off the spacecraft in 2014.

Space safety

Envisat poses a hazard because of the risk of collisions with

space debris Space debris (also known as space junk, space pollution, space waste, space trash, space garbage, or cosmic debris) are defunct human-made objects in spaceprincipally in Earth orbitwhich no longer serve a useful function. These include dere ...

. Given its orbit and its area-to-mass ratio, it will take about 150 years for the satellite to be gradually pulled into the Earth's atmosphere."Envisat To Pose Big Orbital Debris Threat for 150 Years, Experts Say."
''SpaceNews''. Retrieved: 27 September 2015. Envisat is currently orbiting in an environment where two catalogued space debris objects can be expected to pass within about of it every year, which would likely trigger the need for a manoeuvre to avoid a possible collision. A collision between a satellite the size of Envisat and an object as small as 10 kg could produce a very large cloud of debris, initiating a self-sustaining chain-reaction of collisions and fragmentation with production of new debris, a phenomenon known as the

Kessler Syndrome The Kessler syndrome, also known as the Kessler effect, collisional cascading, or ablation cascade, is a scenario proposed by NASA scientists Donald J. Kessler and Burton G. Cour-Palais in 1978. It describes a situation in which the density of o ...

. Envisat was a candidate for a mission to remove it from orbit, called e.Deorbit. The spacecraft sent to bring down Envisat would itself need to have a mass of approximately 1.6 tonnes.

References

External links

Envisat homepage at ESA

Miravi
– Meris Image Rapid Visualization. MIRAVI shows the gallery of images generated on the Level0 (raw data) Meris Full Resolution (300m) products, few seconds after their availability.
SRRS
– Satellite Rapid Response System. Like MIRAVI but including also ASAR, MERIS Full and Reduced Resolution and ALOS AVNIR2 images.
Earth Snapshot
– Web Portal dedicated to Earth Observation. Includes commented satellite images, information on storms, hurricanes, fires and meteorological phenomena.
ESA SNAP Toolbox
for viewing, calibrating and analyzing Envisat ASAR Level 1 data and higher

Physorg.com (2006-02-28)

gcs Global Communication & Services
– Manufacturer of the Envisat DDS Commercial Receiver Kit fo
ENVIHAM Home Users

* ttps://www.eoportal.org/satellite-missions/envisat Envisat article on eoPortal by ESA {{Authority control Earth observation satellites of the European Space Agency Derelict satellites orbiting Earth Space synthetic aperture radar Spacecraft launched in 2002 Spacecraft launched by Ariane rockets Earth satellite radar altimeters Satellites in low Earth orbit