Envisat
Encyclopedia
Envisat is an Earth-observing satellite
. It was launched on 1 March 2002 aboard an Ariane 5
from the Guyana Space Centre in Kourou
, French Guyana into a Sun synchronous polar orbit
at an altitude of 790 km (490.9 mi) (± 10 km (6.2 mi)). It orbit
s the Earth
in about 101 minute
s with a repeat cycle of 35 days.
This €
2.3 billion European Space Agency
(ESA) programme launched the largest earth observation satellite put into space (as of late 2006), being 26 m (85.3 ft) × 10 m (32.8 ft) × 5 m (16.4 ft) and having a mass of 8.5 t (8.4 LT).
. Its objective is 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 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
(humidity
, flood
s), agriculture and arboriculture, natural hazards, digital elevation model
ling (using interferometry
), monitoring of maritime traffic, atmospheric dispersion modelling (pollution), cartography
and study of snow
and ice
.
, ice
, and atmosphere
) using a variety of measurement principles. A tenth instrument, DORIS, provides guidance and control
.
Several of the instruments are advanced versions of instruments that were flown on the earlier ERS 1 and ERS 2 missions and other satellites.
) 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
.
) can measure the temperature of the sea
surface.
It is a passive radiometer which aims to measure the tempemissions from the surface of the earth in the visible
and infrared spectra. Because of its wide angle lens it is possible to make very precise measurements of atmospheric effects on how emissions from the Earth's surface propagate.
AATSR 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 0.3 K-change, 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.
. 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 20 to 80 km (12.4 to 49.7 mi) altitude. It has a resolution of 3 km (1.9 mi).
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 to 1,700 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.
Altimeter
2) is a dual-frequency
Nadir
pointing Radar operating in the Ku band
and S band
s, it is used to define ocean
topography
, map/monitor sea ice
and measure land heights.
Radiometer) for measuring water vapour in the atmosphere
and estimate the tropospheric
delay for the Altimeter
Orbitography and Radiopositioning Integrated by Satellite) determines the satellite's orbit to within 10 centimetres (3.9 in).
Monitoring by Occultation of Star
s) looks to stars as they descend through the Earth's atmosphere and change color, which also tells a lot about the presence of gas
es such as ozone , and allows for the first time a space-based measurement of the vertical distribution of these trace gases.
) is a Fourier transform
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 globe in all seasons and at equal quality night and day. MIPAS has a vertical resolution of 3 to 5 km (1.9 to 3.1 mi) depending on altitude (the larger at the level of the upper stratosphere).
in a wide variety of modes. It can detect changes in surface heights with sub-millimeter precision. It serves 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):
Data capture in WV mode is unusual in that they constitute a series of 5 km × 5 km spaced at 100 km.
Earth observation satellite
Earth observation satellites are satellites specifically designed to observe Earth from orbit, similar to reconnaissance satellites but intended for non-military uses such as environmental monitoring, meteorology, map making etc....
. It was launched on 1 March 2002 aboard an Ariane 5
Ariane 5
Ariane 5 is, as a part of Ariane rocket family, an expendable launch system used to deliver payloads into geostationary transfer orbit or low Earth orbit . Ariane 5 rockets are manufactured under the authority of the European Space Agency and the Centre National d'Etudes Spatiales...
from the Guyana Space Centre in Kourou
Kourou
Kourou is a commune in French Guiana, an overseas region and department of France located in South America.Kourou is the location of the Guiana Space Centre, France and ESA's main spaceport.-Geography:...
, French Guyana into a Sun synchronous polar orbit
Polar orbit
A polar orbit is an orbit in which a satellite passes above or nearly above both poles of the body being orbited on each revolution. It therefore has an inclination of 90 degrees to the equator...
at an altitude of 790 km (490.9 mi) (± 10 km (6.2 mi)). It orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
s the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
in about 101 minute
Minute
A minute is a unit of measurement of time or of angle. The minute is a unit of time equal to 1/60th of an hour or 60 seconds. In the UTC time scale, a minute on rare occasions has 59 or 61 seconds; see leap second. The minute is not an SI unit; however, it is accepted for use with SI units...
s with a repeat cycle of 35 days.
This €
Euro
The euro is the official currency of the eurozone: 17 of the 27 member states of the European Union. It is also the currency used by the Institutions of the European Union. The eurozone consists of Austria, Belgium, Cyprus, Estonia, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg,...
2.3 billion European Space Agency
European Space Agency
The European Space Agency , established in 1975, is an intergovernmental organisation dedicated to the exploration of space, currently with 18 member states...
(ESA) programme launched the largest earth observation satellite put into space (as of late 2006), being 26 m (85.3 ft) × 10 m (32.8 ft) × 5 m (16.4 ft) and having a mass of 8.5 t (8.4 LT).
Mission
Envisat is an Earth observation satelliteEarth observation satellite
Earth observation satellites are satellites specifically designed to observe Earth from orbit, similar to reconnaissance satellites but intended for non-military uses such as environmental monitoring, meteorology, map making etc....
. Its objective is to service the continuity of European Remote-Sensing Satellite
European Remote-Sensing Satellite
European remote sensing satellite was the European Space Agency's first Earth-observing satellite. It was launched on July 17, 1991 into a Sun-synchronous polar orbit at a height of 782–785 km.-Instruments:...
missions, providing additional observational parameters to improve environmental studies.
In working towards the global and regional objectives of the mission, numerous scientific disciplines use the data acquired from the different sensors on the satellite, to study such things as atmospheric chemistry
Atmospheric chemistry
Atmospheric chemistry is a branch of atmospheric science in which the chemistry of the Earth's atmosphere and that of other planets is studied. It is a multidisciplinary field of research and draws on environmental chemistry, physics, meteorology, computer modeling, oceanography, geology and...
, ozone depletion
Ozone depletion
Ozone depletion describes two distinct but related phenomena observed since the late 1970s: a steady decline of about 4% per decade in the total volume of ozone in Earth's stratosphere , and a much larger springtime decrease in stratospheric ozone over Earth's polar regions. The latter phenomenon...
, biological oceanography, ocean temperature and colour, wind waves, hydrology
Hydrology
Hydrology is the study of the movement, distribution, and quality of water on Earth and other planets, including the hydrologic cycle, water resources and environmental watershed sustainability...
(humidity
Humidity
Humidity is a term for the amount of water vapor in the air, and can refer to any one of several measurements of humidity. Formally, humid air is not "moist air" but a mixture of water vapor and other constituents of air, and humidity is defined in terms of the water content of this mixture,...
, flood
Flood
A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...
s), agriculture and arboriculture, natural hazards, digital elevation model
Digital elevation model
A digital elevation model is a digital model or 3-D representation of a terrain's surface — commonly for a planet , moon, or asteroid — created from terrain elevation data....
ling (using interferometry
Interferometry
Interferometry refers to a family of techniques in which electromagnetic waves are superimposed in order to extract information about the waves. An instrument used to interfere waves is called an interferometer. Interferometry is an important investigative technique in the fields of astronomy,...
), monitoring of maritime traffic, atmospheric dispersion modelling (pollution), cartography
Cartography
Cartography is the study and practice of making maps. Combining science, aesthetics, and technique, cartography builds on the premise that reality can be modeled in ways that communicate spatial information effectively.The fundamental problems of traditional cartography are to:*Set the map's...
and study of snow
Snow
Snow is a form of precipitation within the Earth's atmosphere in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by...
and ice
Ice
Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...
.
Instruments
Envisat carries an array of nine Earth-observation instruments that gather information about the earth (land, waterWater
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
, ice
Ice
Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...
, and atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
) using a variety of measurement principles. A tenth instrument, DORIS, provides guidance and control
Guidance, Navigation and Control
Guidance, navigation and control is a branch of engineering dealing with the design of systems to control the movement of vehicles, especially, automobiles, ships, aircraft, and spacecraft. In many cases these functions can be performed by trained humans...
.
Several of the instruments are advanced versions of instruments that were flown on the earlier ERS 1 and ERS 2 missions and other satellites.
MERIS
MERIS (MEdium Resolution Imaging SpectrometerSpectrometer
A spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the light's intensity but could also, for instance, be the polarization...
) measures the reflectance of the Earth (surface and atmosphere) in the solar spectral range (390 to 1040 nm
Nanometre
A nanometre is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- with the parent unit name metre .The nanometre is often used to express dimensions on the atomic scale: the diameter...
) and transmits 15 spectral bands back to the ground segment.
MERIS was built at the Cannes Mandelieu Space Center
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...
.
AATSR
AATSR (Advanced Along Track Scanning RadiometerRadiometer
A radiometer is a device for measuring the radiant flux of electromagnetic radiation. Generally, the term radiometer denotes an infrared radiation detector, yet it also includes detectors operating on any electromagnetic wavelength....
) can measure the temperature of the sea
Sea
A sea generally refers to a large body of salt water, but the term is used in other contexts as well. Most commonly, it means a large expanse of saline water connected with an ocean, and is commonly used as a synonym for ocean...
surface.
It is a passive radiometer which aims to measure the tempemissions from the surface of the earth in the visible
Visible spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 750 nm. In terms of...
and infrared spectra. Because of its wide angle lens it is possible to make very precise measurements of atmospheric effects on how emissions from the Earth's surface propagate.
AATSR 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 0.3 K-change, for climate research
Climatology
Climatology is the study of climate, scientifically defined as weather conditions averaged over a period of time, and is a branch of the atmospheric sciences...
.
Among the secondary objectives of AATSR is the observation of environmental parameters such as water content, biomass, and vegetal health and growth.
GOMOS
GOMOS (Global Ozone Monitoring by Occultation of Stars) uses the principle of occultationOccultation
An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...
. 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 20 to 80 km (12.4 to 49.7 mi) altitude. It has a resolution of 3 km (1.9 mi).
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 to 1,700 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.
RA-2
RA-2 (RadarRadar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
Altimeter
Altimeter
An altimeter 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 underwater.-Pressure altimeter:...
2) is a dual-frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
Nadir
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 there. Since the concept of being below is itself somewhat vague, scientists define the nadir in more rigorous...
pointing Radar operating in the Ku band
Ku band
The Kμ band is a portion of the electromagnetic spectrum in the microwave range of frequencies. This symbol refers to —in other words, the band directly below the K-band...
and S band
S band
The S band is defined by an IEEE standard for radio waves with frequencies that range from 2 to 4 GHz, crossing the conventional boundary between UHF and SHF at 3.0 GHz. It is part of the microwave band of the electromagnetic spectrum...
s, it is used to define ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
topography
Topography
Topography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...
, map/monitor sea ice
Sea ice
Sea ice is largely formed from seawater that freezes. Because the oceans consist of saltwater, this occurs below the freezing point of pure water, at about -1.8 °C ....
and measure land heights.
MWR
MWR (MicrowaveMicrowave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
Radiometer) for measuring water vapour in the atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
and estimate the tropospheric
Troposphere
The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....
delay for the Altimeter
Altimeter
An altimeter 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 underwater.-Pressure altimeter:...
DORIS
DORIS (DopplerDoppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
Orbitography and Radiopositioning Integrated by Satellite) determines the satellite's orbit to within 10 centimetres (3.9 in).
GOMOS
GOMOS (Global OzoneOzone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...
Monitoring by Occultation of Star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s) looks to stars as they descend through the Earth's atmosphere and change color, which also tells a lot about the presence of gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
es such as ozone , and allows for the first time a space-based measurement of the vertical distribution of these trace gases.
MIPAS
MIPAS (Michelson Interferometer for Passive Atmospheric SoundingAtmospheric sounding
An atmospheric sounding is a measurement of vertical distribution of physical properties of the atmospheric column such as pressure, temperature, wind speed and wind direction , liquid water content, ozone concentration, pollution, and other properties...
) is a Fourier transform
Fourier transform
In mathematics, Fourier analysis is a subject area which grew from the study of Fourier series. The subject began with the study of the way general functions may be represented by sums of simpler trigonometric functions...
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 globe in all seasons and at equal quality night and day. MIPAS has a vertical resolution of 3 to 5 km (1.9 to 3.1 mi) depending on altitude (the larger at the level of the upper stratosphere).
ASAR
ASAR (Advanced Synthetic Aperture Radar) operates in the C bandC band
The C band is a name given to certain portions of the electromagnetic spectrum, including wavelengths of microwaves that are used for long-distance radio telecommunications. The IEEE C-band - and its slight variations - contains frequency ranges that are used for many satellite communications...
in a wide variety of modes. It can detect changes in surface heights with sub-millimeter precision. It serves 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.
| 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 × 5 km | |
| Suivi global (ScanSAR) | GM | HH, VV | 1 km | 405 km | |
| Wavescan (ScanSAR) | WS | HH, VV | 150 m | 405 km |
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.
External links
- Envisat-homepage at ESA
- Envisat operations page 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.
- Next ESA SAR Toolbox for viewing, calibrating and analyzing Envisat ASAR Level 1 data and higher
- Four years on, Envisat hailed for its contribution to Earth science Physorg.com (2006-02-28)
- ESA Envisat DDS (Data Dissemination System)
- gcs Global Communication & Services - Manufacturer of the Envisat DDS Commercial Receiver Kit for ENVIHAM Home Users