Envisat ("Environmental Satellite") is a large inactive
Earth-observing 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 ...
which is still in orbit and now considered space debris. Operated by the
European Space Agency
, owners =
, headquarters = Paris, Île-de-France, France
, coordinates =
, spaceport = Guiana Space Centre
, seal = File:ESA emblem seal.png
, seal_size = 130px
, image = Views in the Main Control Room (120 ...
(ESA), it was the world's largest civilian Earth observation satellite.
It was launched on 1 March 2002 aboard an
Ariane 5 from the
Guyana Space Centre
The Guiana Space Centre (french: links=no, Centre spatial guyanais; CSG), also called Europe's Spaceport, is a European spaceport to the northwest of Kourou in French Guiana, a region of France in South America. Kourou is located approxim ...
in
Kourou,
French Guiana
French Guiana ( or ; french: link=no, Guyane ; gcr, label= French Guianese Creole, Lagwiyann ) is an overseas department/region and single territorial collectivity of France on the northern Atlantic coast of South America in the Guianas ...
, into a
Sun synchronous polar orbit at an altitude of 790 ± 10 km. It
orbit
In celestial mechanics, an orbit 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 object or position in space such as ...
s the
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's sur ...
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 The mission has been replaced by the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 gran ...
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. Its objective was to service the continuity of
European Remote-Sensing Satellite missions, providing additional observational parameters to improve environmental studies.
In working towards the global and regional objectives of the mission, numerous scientific disciplines currently use the data acquired from the different sensors on the satellite to study such things as
atmospheric chemistry,
ozone depletion,
biological oceanography, 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 environmental watershed sustainability. A practitioner of hydrology is call ...
(
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, dew, or fog to be present.
Humidity dep ...
,
flood
A flood is an overflow of water ( 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 an area of study of the discipline hydrol ...
s), agriculture and arboriculture, natural hazards,
digital elevation modelling (using
interferometry), monitoring of maritime traffic,
atmospheric dispersion modelling (pollution),
cartography
Cartography (; from grc, χάρτης , "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 i ...
and study of
snow
Snow comprises 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 throughou ...
and
ice.
Specifications
;Dimensions
× × in orbit with the solar array deployed.
;Mass
, including of fuel and a instrument payload.
;Power
Solar array
A photovoltaic system, also PV system or solar power system, is an electric power system designed to supply usable solar power by means of photovoltaics. It consists of an arrangement of several components, including solar panels to absorb and ...
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 (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...
,
ice, and
atmosphere) 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
European Remote Sensing satellite (ERS) was the European Space Agency's first Earth-observing satellite programme using a polar orbit. It consisted of 2 satellites, ERS-1 and ERS-2.
ERS-1
ERS-1 launched 17 July 1991 from Guiana Space Centr ...
and
ERS 2 missions and other satellites.
MWR
MWR (
Microwave
Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ra ...
Radiometer) was designed for measuring
water vapour in the
atmosphere.
AATSR
AATSR (Advanced Along Track Scanning
Radiometer) can measure the
sea
The sea, connected as the world ocean or simply the ocean, is the body of salty water that covers approximately 71% of the Earth's surface. The word sea is also used to denote second-order sections of the sea, such as the Mediterranean Sea, ...
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 for Passive
Atmospheric Sounding Atmospheric sounding or atmospheric profiling is a measurement of vertical distribution of physical properties of the atmospheric column such as pressure, temperature, wind speed and wind direction (thus deriving wind shear), liquid water content, ...
) is a
Fourier transform
A Fourier transform (FT) is a mathematical transform that decomposes functions into frequency components, which are represented by the output of the transform as a function of frequency. Most commonly functions of time or space are transformed ...
ing infrared spectrometer which provides pressure and temperature profiles, and profiles of trace gases nitrogen dioxide (), nitrous oxide (), methane (), nitric acid (), ozone (), and water () in the
stratosphere. 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) 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. MERIS was built at the
Cannes Mandelieu Space Center
The Cannes Mandelieu Space Center is an industrial plant dedicated to spacecraft manufacturing, located in both the towns of Cannes and Mandelieu in France. After a long history in aircraft manufacturing, starting in 1929, the center became incre ...
.
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 detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, Marine radar, ships, spacecraft, guided missiles, motor v ...
Altimeter 2) is a dual-
frequency
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
Nadir pointing Radar operating in the
Ku 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 conventi ...
s, it is used to define
ocean
The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wor ...
topography
Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the land forms and features themselves, or a description or depiction in maps.
Topography is a field of geoscience and planetary sc ...
, map/monitor
sea ice and measure land heights.
Mean sea level measurements from Envisat are continuously graphed at th
Centre National d'Etudes Spatialesweb site, on th
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 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 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 , breaking down in the l ...
Monitoring by Occultation of
Star
A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
s) looks at stars as they descend through the Earth's atmosphere and change color, 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 ...
. 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 .
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 The Seven Sisters, Messier 45 and other names by different cultures, is an asterism and an open star cluster containing middle-aged, hot B-type stars in the north-west of the constellation Taurus. At a distance ...
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 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. 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.[
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.]
See also
*List of heaviest spacecraft
The heaviest artificial objects to reach space include space stations, various upper stages, and discarded Space Shuttle external tanks. Spacecraft may change mass over time such as by use of propellant.
During the Shuttle–' ...
* List of large reentering space debris
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
{{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