AATSR
Encyclopedia
The Advanced Along Track Scanning Radiometer (AATSR) is one of the Announcement of Opportunity (AO) instruments on board the European Space Agency
(ESA)'s Envisat
satellite.
This instrument is a multi-channel imaging radiometer
with the principal objective of providing data concerning global Sea Surface Temperature (SST) to the high levels of accuracy and stability required for monitoring and carrying out research into the behaviour of the Earth’s climate
.
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 aerosols, clouds, fires, gas flares, water content, biomass, and vegetal health and growth.
AATSR is the successor of ATSR-1 and ATSR-2, payloads of ERS-1 and ERS-2.
In order to achieve this accuracy while viewing the Earth's surface through the atmosphere, AATSR views the surface at two angles, one close to the nadir
(immediately below the satellite) and the other along the satellite track at close to 55° from the nadir, thereby providing two views of each point on the Earth's surface, each with a different effective atmospheric thickness. This dual-view system enables a particularly accurate estimate to be made of the signal degradation due to atmospheric absorption and scattering.
AATSR also embodies an exceptionally precise and stable on-board calibration system, comprising two reference targets specially designed for high uniformity and stability. These two targets, known as ‘black bodies’
are maintained at temperatures near to the extremes of the Earth temperatures as measured by AATSR and they are both viewed during each scan cycle of the instrument. This calibration system ensures that measurements of thermal radiation from the Earth’s surface are properly calibrated and do not rely on ground-based measurements, although such measurements are continually used to evaluate AATSR’s performance.
AATSR has three channels at thermal infrared wavelengths, from which surface temperatures are derived over both sea and land surfaces. In addition, AATSR has four visible and near-infrared wavelength channels which are used to identify cloudy areas and to measure solar radiation that is scattered and reflected from the Earth’s surface and atmosphere. These channels provide measurements from which land-cover properties, for example, NDVI
, as well as clouds and atmospheric particulate matter (or aerosol
s) can be studied. The dual-view measurements provided by the along-track scanning technique is also a key feature of AATSR when used for atmospheric or vegetation measurements. As with the SST measurements, the two measurements of each point on the surface through different atmospheric path lengths greatly simplifies the task of separating the surface and atmospheric contributions to the measured signal. Thus the effects of atmospheric aerosols can be removed from surface products (such as surface reflectance or NDVI). Conversely, a similar approach can be used to account for the surface reflectance in determining aerosol or cloud properties. Additionally, the parallax
between the two views can be used to determine cloud top
and aerosol plume heights using geometric means.
AATSR is the third in a series of instruments started by ATSR-1, which was launched in 1991 on the European Remote-Sensing Satellite, ERS-1
. This was followed by ATSR-2 on ERS-2 in 1995 and by AATSR on the Envisat satellite in 2002. The original ATSR-1 instrument lacked the three shortest wavelength channels provided by AATSR, whereas ATSR-2 was functionally identical. This has led to a near-continuous SST dataset extending from 1991 to the present day. Looking to the future, a successor instrument is being developed to fly on ESA’s Sentinel 3
satellite, which is part of the space segment of the European Global Monitoring for Environment and Security (GMES)
programme. This will ensure the continuity of AATSR-standard SST data into the foreseeable future.
One of the most important aspects of the ATSR series of space instruments is that it has, over a period of just over 15 years, undergone the transition from experimental sensor on the ERS satellites, developing the technique and demonstrating the accuracy that can be achieved with along-track scanning, to that of an operational system, within Europe’s Envisat and future GMES Programmes.
The AATSR is a nationally-provided instrument, funded by the UK’s Department for Environment, Food and Rural Affairs (Defra) in order to support their programme of climate prediction and research. It was developed and is operated in collaboration with ESA. There is also a significant Australian contribution to the AATSR programme, now managed by the Commonwealth Scientific and Industrial Research Organisation. The predecessor instruments, ATSR-1 and ATSR-2, were funded by the UK's Science and Engineering Research Council. This funding responsibility was transferred to the UK's Natural Environment Research Council
in 1993.
Earth observational satellite will house many earth observational instruments including SLSTR (Sea and Land Surface Temperature Radiometer) which is the successor to AATSR.
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)'s Envisat
Envisat
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...
satellite.
This instrument is a multi-channel imaging radiometer
Radiometer
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....
with the principal objective of providing data concerning global Sea Surface Temperature (SST) to the high levels of accuracy and stability required for monitoring and carrying out research into the behaviour of the Earth’s climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...
.
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 aerosols, clouds, fires, gas flares, water content, biomass, and vegetal health and growth.
AATSR is the successor of ATSR-1 and ATSR-2, payloads of ERS-1 and ERS-2.
Details
The required accuracies are better than 0.3 °C with a stability approaching 0.1 °C /decade. 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.In order to achieve this accuracy while viewing the Earth's surface through the atmosphere, AATSR views the surface at two angles, one close to the 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...
(immediately below the satellite) and the other along the satellite track at close to 55° from the nadir, thereby providing two views of each point on the Earth's surface, each with a different effective atmospheric thickness. This dual-view system enables a particularly accurate estimate to be made of the signal degradation due to atmospheric absorption and scattering.
AATSR also embodies an exceptionally precise and stable on-board calibration system, comprising two reference targets specially designed for high uniformity and stability. These two targets, known as ‘black bodies’
Black body
A black body is an idealized physical body that absorbs all incident electromagnetic radiation. Because of this perfect absorptivity at all wavelengths, a black body is also the best possible emitter of thermal radiation, which it radiates incandescently in a characteristic, continuous spectrum...
are maintained at temperatures near to the extremes of the Earth temperatures as measured by AATSR and they are both viewed during each scan cycle of the instrument. This calibration system ensures that measurements of thermal radiation from the Earth’s surface are properly calibrated and do not rely on ground-based measurements, although such measurements are continually used to evaluate AATSR’s performance.
AATSR has three channels at thermal infrared wavelengths, from which surface temperatures are derived over both sea and land surfaces. In addition, AATSR has four visible and near-infrared wavelength channels which are used to identify cloudy areas and to measure solar radiation that is scattered and reflected from the Earth’s surface and atmosphere. These channels provide measurements from which land-cover properties, for example, NDVI
Normalized Difference Vegetation Index
The Normalized Difference Vegetation Index is a simple graphical indicator that can be used to analyze remote sensing measurements, typically but not necessarily from a space platform, and assess whether the target being observed contains live green vegetation or not.-Brief history:The exploration...
, as well as clouds and atmospheric particulate matter (or aerosol
Aerosol
Technically, an aerosol is a suspension of fine solid particles or liquid droplets in a gas. Examples are clouds, and air pollution such as smog and smoke. In general conversation, aerosol usually refers to an aerosol spray can or the output of such a can...
s) can be studied. The dual-view measurements provided by the along-track scanning technique is also a key feature of AATSR when used for atmospheric or vegetation measurements. As with the SST measurements, the two measurements of each point on the surface through different atmospheric path lengths greatly simplifies the task of separating the surface and atmospheric contributions to the measured signal. Thus the effects of atmospheric aerosols can be removed from surface products (such as surface reflectance or NDVI). Conversely, a similar approach can be used to account for the surface reflectance in determining aerosol or cloud properties. Additionally, the parallax
Parallax
Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. The term is derived from the Greek παράλλαξις , meaning "alteration"...
between the two views can be used to determine cloud top
Cloud top
The cloud top is the highest altitude of the visible portion of the cloud. It is traditionally expressed either in metres above the Earth surface, or as the corresponding pressure level in hectopascal .-Measurement:The cloud top is where the snow, rain and sleet come from.Cloud top...
and aerosol plume heights using geometric means.
AATSR is the third in a series of instruments started by ATSR-1, which was launched in 1991 on the European Remote-Sensing Satellite, ERS-1
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:...
. This was followed by ATSR-2 on ERS-2 in 1995 and by AATSR on the Envisat satellite in 2002. The original ATSR-1 instrument lacked the three shortest wavelength channels provided by AATSR, whereas ATSR-2 was functionally identical. This has led to a near-continuous SST dataset extending from 1991 to the present day. Looking to the future, a successor instrument is being developed to fly on ESA’s Sentinel 3
Sentinel 3
Sentinel 3 is a future space mission from ESA, the third in the GMES program.It will provide medium resolution optical and radar altimetry Earth observation data...
satellite, which is part of the space segment of the European Global Monitoring for Environment and Security (GMES)
GMES
Global Monitoring for Environment and Security is a joint initiative of the European Commission and European Space Agency, which aims at achieving an autonomous and operational Earth observation capacity....
programme. This will ensure the continuity of AATSR-standard SST data into the foreseeable future.
One of the most important aspects of the ATSR series of space instruments is that it has, over a period of just over 15 years, undergone the transition from experimental sensor on the ERS satellites, developing the technique and demonstrating the accuracy that can be achieved with along-track scanning, to that of an operational system, within Europe’s Envisat and future GMES Programmes.
The AATSR is a nationally-provided instrument, funded by the UK’s Department for Environment, Food and Rural Affairs (Defra) in order to support their programme of climate prediction and research. It was developed and is operated in collaboration with ESA. There is also a significant Australian contribution to the AATSR programme, now managed by the Commonwealth Scientific and Industrial Research Organisation. The predecessor instruments, ATSR-1 and ATSR-2, were funded by the UK's Science and Engineering Research Council. This funding responsibility was transferred to the UK's Natural Environment Research Council
Natural Environment Research Council
The Natural Environment Research Council is a British research council that supports research, training and knowledge transfer activities in the environmental sciences.-History:...
in 1993.
Successor
The Sentinel 3Sentinel 3
Sentinel 3 is a future space mission from ESA, the third in the GMES program.It will provide medium resolution optical and radar altimetry Earth observation data...
Earth observational satellite will house many earth observational instruments including SLSTR (Sea and Land Surface Temperature Radiometer) which is the successor to AATSR.