Advanced Microwave Sounding Unit
Encyclopedia
The Advanced microwave sounding unit
(AMSU) is a multi-channel microwave radiometer
installed on meteorological satellites. The instrument examines several bands of microwave radiation from the atmosphere to perform atmospheric sounding
of temperature and moisture levels.
s.
Level-2 geophysical data from AMSU include:
AMSU data is also used together with infrared radiances from HIRS, AIRS, or IASI to produce blended MW/IR level-2 geophysical products such as:
(NWP) centers around the world. This data helps keep the assessment of the current state of the atmosphere correct, which in turn helps make predictions more accurate.
Long-term AMSU records are also used in studies of climate
.
(NOAA K), launched May 13 1998; NOAA-16
(NOAA L), launched September 21, 2000; and NOAA-17
(NOAA M), launched June 24, 2002.
For NOAA-18
(NOAA N), launched May 20, 2005, AMSU-B was replaced by a similar instrument, the Microwave Humidity Sounder
(MHS).
Versions of AMSU-A also fly on the NASA
Aqua
Earth science satellite and the EUMETSAT
MetOp
series. On these spacecraft, AMSU-B is replaced by similar microwave humidity sounders: HSB
for Aqua and MHS
for MetOp.
The AMSU was an improvement of the Microwave Sounding Unit
(MSU), incorporating capabilities of the Stratospheric Sounding Unit (SSU), both of which had flown on TIROS
-N in 1978 and continued on the NOAA-6 through NOAA-14 satellites. The next generation in the family is Advanced Technology Microwave Sounder (ATMS), slated for launch on NPP and NPOESS
satellites starting in 2009 or 2010.
AMSUs were manufactured by Aerojet
Corporation in Azusa, California
. This organization is now part of Northrop Grumman Electronic Systems
.
s. This results in their crossing the equator at the same two local solar times every orbit. For example EOS Aqua crosses the equator in daylight heading north (ascending) at 1:30 pm solar time
and in darkness heading south (descending) at 1:30 am solar time.
The AMSU instruments scan continuously in a "whisk broom" mode. During about 6 seconds of each 8-second observation cycle, AMSU-A makes 30 observations at 3.3° steps from −48° to +48°. It then makes observations of a warm calibration target and of cold space before it returns to its original position for the start of the next scan. In these 8 seconds the subsatellite point moves about 45 km, so the next scan will be 45 km further along the track. AMSU-B meanwhile makes 3 scans of 90 observations each, with a spacing of 1.1°.
During any given 24-hour period there are approximately 16 orbits. Almost the entire globe is observed in either daylight or nighttime mode, many in both. Polar regions are observed nearly every 100 minutes.
, and is used primarily for measuring atmospheric temperatures (known as "temperature sounding"). It has a ground resolution
near nadir of 45 km. AMSU-B, with five channels between 89 and 183.3 GHz, has a spatial resolution near nadir of 15 km and is primarily intended for moisture sounding. Spot size of both sub-instruments becomes larger and more elongated toward the edges of the swath. When the two instruments are used together, there are roughly 9 AMSU-B fields-of-view in a 3x3 array corresponding to each AMSU-A field-of-view. This reflects the higher spatial variability of water vapor compared to temperature. HIRS/3 infrared sounders with the same spatial resolution as AMSU-B are also included on NOAA 15-17 satellites and are used together with AMSU-A and AMSU-B. Together the three instruments form ATOVS, the Advanced TIROS Operational Vertical Sounder.
The Aqua and MetOp AMSU-A instruments are 15-channel microwave sounders designed primarily to obtain temperature profiles in the upper atmosphere (especially the stratosphere
) and to provide a cloud-filtering capability for tropospheric temperature observations. The EOS AMSU-A is part of a closely coupled triplet of instruments that include the AIRS
and HSB
. The MetOp AMSU-A similarly works with HIRS, IASI, and MHS. MHS and HSB are variants on AMSU-B.
Table 1 Radiometric characteristics of the AMSU-A (from 3,5).
Table 2 Radiometric characteristics of the AMSU-B (from 4).
Microwave sounding unit
The Microwave sounding unit was the predecessor to the Advanced Microwave Sounding Unit.The MSU was first launched aboard the TIROS-N satellitein late 1978 and provided global coverage...
(AMSU) is a multi-channel microwave 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....
installed on meteorological satellites. The instrument examines several bands of microwave radiation from the atmosphere to perform atmospheric sounding
Atmospheric 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...
of temperature and moisture levels.
Products
Level-1 radiance data are calibrated brightness temperatureBrightness temperature
Brightness temperature is the temperature a black body in thermal equilibrium with its surroundings would have to be to duplicate the observed intensity of a grey body object at a frequency \nu....
s.
Level-2 geophysical data from AMSU include:
- Temperature profile from 3 mbarBar (unit)The bar is a unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the megabar , kilobar , decibar , centibar , and millibar...
(45 km) to the surface - Water vapor profiles
- Snow and ice coverage
- Cloud liquid water
- Rain Rate
AMSU data is also used together with infrared radiances from HIRS, AIRS, or IASI to produce blended MW/IR level-2 geophysical products such as:
- Temperature profiles
- Water vapor profiles
- Ozone
- Cloud properties
- Cloud-cleared IR radiances
Applications
AMSU data is used extensively in weather prediction. Brightness temperatures are processed as quickly as possible and sent to numerical weather predictionNumerical weather prediction
Numerical weather prediction uses mathematical models of the atmosphere and oceans to predict the weather based on current weather conditions. Though first attempted in the 1920s, it was not until the advent of computer simulation in the 1950s that numerical weather predictions produced realistic...
(NWP) centers around the world. This data helps keep the assessment of the current state of the atmosphere correct, which in turn helps make predictions more accurate.
Long-term AMSU records are also used in studies of 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...
.
History
AMSU-A + AMSU-B have flown together on the 3 NOAA KLM satellites: NOAA-15NOAA-15
NOAA-15 is one of the NASA-provided TIROS series of weather forecasting satellite run by NOAA. It was launched on 13 May 1998, and is currently operational, in a sun-synchronous orbit, 807 km above the Earth, orbiting every 101 minutes...
(NOAA K), launched May 13 1998; NOAA-16
NOAA-16
NOAA-16 is one of the NASA-provided TIROS series of weather forecasting satellite run by NOAA. It was launched on 21 September 2000, and is currently operational, in a sun-synchronous orbit, 849 km above the Earth, orbiting every 102 minutes. It hosts the AMSU, AVHRR and High Resolution...
(NOAA L), launched September 21, 2000; and NOAA-17
NOAA-17
NOAA-17 is a weather forecasting satellite run by NOAA. It was launched on 24 June 2002, and is currently operational, in a sun-synchronous orbit, 824 km above the Earth, orbiting every 101 minutes. It hosts the AMSU, AVHRR and High Resolution Infrared Radiation Sounder instruments.APT...
(NOAA M), launched June 24, 2002.
For NOAA-18
NOAA-18
NOAA-18 is a weather forecasting satellite run by NOAA. NOAA-N was launched on May 20, 2005, into a sun-synchronous orbit at an altitude of 854 km above the Earth, with an orbital period of 102 minutes. It hosts the AMSU-A, MHS, AVHRR and High Resolution Infrared Radiation Sounder instruments, as...
(NOAA N), launched May 20, 2005, AMSU-B was replaced by a similar instrument, the Microwave Humidity Sounder
Microwave humidity sounder
The Microwave Humidity Sounder is an instrument launched on NOAA's POES satellite series starting with NOAA-18 launched in May 2005 and European Space Agency's MetOp series starting with MetOp-A launched in October 2006. It is a five-channel passive microwave radiometer, with channels from 89 to...
(MHS).
Versions of AMSU-A also fly on the NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
Aqua
Aqua (satellite)
Aqua is a multi-national NASA scientific research satellite in orbit around the Earth, studying the precipitation, evaporation, and cycling of water. It is the second major component of the Earth Observing System preceded by Terra and followed by Aura .The name "Aqua" comes from the Latin word...
Earth science satellite and the EUMETSAT
European Organisation for the Exploitation of Meteorological Satellites
EUMETSAT is an intergovernmental organisation created through an international convention agreed by a current total of 26 European Member States: Austria, Belgium, Croatia, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Ireland, Romania, Italy, Latvia, Luxembourg, the...
MetOp
MetOp
MetOp is a series of polar orbiting meteorological satellites operated by the European Organisation for the Exploitation of Meteorological Satellites. The satellites are all part af the EUMETSAT Polar System. It is intended to replace the soon to be retired TIROS network...
series. On these spacecraft, AMSU-B is replaced by similar microwave humidity sounders: HSB
Humidity Sounder for Brazil
The Humidity Sounder for Brazil was an instrument launched on NASA's Earth Observing System satellite Aqua launched in May 2002. It was a four-channel passive microwave radiometer, with one channel at 150 GHz and three channels at 183 GHz. It was very similar in design to the AMSU-B instrument,...
for Aqua and MHS
Microwave humidity sounder
The Microwave Humidity Sounder is an instrument launched on NOAA's POES satellite series starting with NOAA-18 launched in May 2005 and European Space Agency's MetOp series starting with MetOp-A launched in October 2006. It is a five-channel passive microwave radiometer, with channels from 89 to...
for MetOp.
The AMSU was an improvement of the Microwave Sounding Unit
Microwave sounding unit
The Microwave sounding unit was the predecessor to the Advanced Microwave Sounding Unit.The MSU was first launched aboard the TIROS-N satellitein late 1978 and provided global coverage...
(MSU), incorporating capabilities of the Stratospheric Sounding Unit (SSU), both of which had flown on TIROS
TIROS
TIROS, or Television Infrared Observation Satellite, is a series of early weather satellites launched by NASA, beginning with TIROS-1 in 1960. TIROS was the first satellite that was capable of remote sensing of the Earth. This initial remote-sensing effort was significant because it enabled Earth...
-N in 1978 and continued on the NOAA-6 through NOAA-14 satellites. The next generation in the family is Advanced Technology Microwave Sounder (ATMS), slated for launch on NPP and NPOESS
NPOESS
The National Polar-orbiting Operational Environmental Satellite System was to be the United States' next-generation satellite system that would monitor the Earth's weather, atmosphere, oceans, land and near-space environment. NPOESS satellites were to host proven technologies and operational...
satellites starting in 2009 or 2010.
AMSUs were manufactured by Aerojet
Aerojet
Aerojet is an American rocket and missile propulsion manufacturer based primarily in Rancho Cordova, California with divisions in Redmond, Washington, Orange, Gainesville and Camden, Arkansas. Aerojet is owned by GenCorp. They are the only US propulsion company that provides both solid rocket...
Corporation in Azusa, California
Azusa, California
Azusa is a city in Los Angeles County, California, United States. The population was 46,361 at the 2010 census, up from 44,712 at the 2000 census. Though sometimes assumed to be a compaction of the phrase "everything from A to Z in the USA" from an old Jack Benny joke, the place name "Azusa"...
. This organization is now part of Northrop Grumman Electronic Systems
Northrop Grumman Electronic Systems
' was created by Northrop Grumman's acquisition of Westinghouse Electronic Systems Group in 1996. The Electronic Systems sector is a leading designer, developer, and manufacturer of a wide variety of advanced defense electronics and systems. The division has 120 locations worldwide, including 72...
.
Observation geometry
AMSUs are always situated on polar-orbiting satellites in sun-synchronous orbitSun-synchronous orbit
A Sun-synchronous orbit is a geocentric orbit which combines altitude and inclination in such a way that an object on that orbit ascends or descends over any given point of the Earth's surface at the same local mean solar time. The surface illumination angle will be nearly the same every time...
s. This results in their crossing the equator at the same two local solar times every orbit. For example EOS Aqua crosses the equator in daylight heading north (ascending) at 1:30 pm solar time
Solar time
Solar time is a reckoning of the passage of time based on the Sun's position in the sky. The fundamental unit of solar time is the day. Two types of solar time are apparent solar time and mean solar time .-Introduction:...
and in darkness heading south (descending) at 1:30 am solar time.
The AMSU instruments scan continuously in a "whisk broom" mode. During about 6 seconds of each 8-second observation cycle, AMSU-A makes 30 observations at 3.3° steps from −48° to +48°. It then makes observations of a warm calibration target and of cold space before it returns to its original position for the start of the next scan. In these 8 seconds the subsatellite point moves about 45 km, so the next scan will be 45 km further along the track. AMSU-B meanwhile makes 3 scans of 90 observations each, with a spacing of 1.1°.
During any given 24-hour period there are approximately 16 orbits. Almost the entire globe is observed in either daylight or nighttime mode, many in both. Polar regions are observed nearly every 100 minutes.
Instrument characteristics
The AMSU has two sub-instruments, AMSU-A and AMSU-B. AMSU-A has 15 channels between 23.8 and 89 GHzGHZ
GHZ or GHz may refer to:# Gigahertz .# Greenberger-Horne-Zeilinger state — a quantum entanglement of three particles.# Galactic Habitable Zone — the region of a galaxy that is favorable to the formation of life....
, and is used primarily for measuring atmospheric temperatures (known as "temperature sounding"). It has a ground resolution
Angular resolution
Angular resolution, or spatial resolution, describes the ability of any image-forming device such as an optical or radio telescope, a microscope, a camera, or an eye, to distinguish small details of an object...
near nadir of 45 km. AMSU-B, with five channels between 89 and 183.3 GHz, has a spatial resolution near nadir of 15 km and is primarily intended for moisture sounding. Spot size of both sub-instruments becomes larger and more elongated toward the edges of the swath. When the two instruments are used together, there are roughly 9 AMSU-B fields-of-view in a 3x3 array corresponding to each AMSU-A field-of-view. This reflects the higher spatial variability of water vapor compared to temperature. HIRS/3 infrared sounders with the same spatial resolution as AMSU-B are also included on NOAA 15-17 satellites and are used together with AMSU-A and AMSU-B. Together the three instruments form ATOVS, the Advanced TIROS Operational Vertical Sounder.
The Aqua and MetOp AMSU-A instruments are 15-channel microwave sounders designed primarily to obtain temperature profiles in the upper atmosphere (especially the stratosphere
Stratosphere
The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...
) and to provide a cloud-filtering capability for tropospheric temperature observations. The EOS AMSU-A is part of a closely coupled triplet of instruments that include the AIRS
Atmospheric Infrared Sounder
The Atmospheric Infrared Sounder is one of six instruments flying on board NASA’s Aqua satellite, launched on May 4, 2002. The instrument is designed to support climate research and improve weather forecasting....
and HSB
Humidity Sounder for Brazil
The Humidity Sounder for Brazil was an instrument launched on NASA's Earth Observing System satellite Aqua launched in May 2002. It was a four-channel passive microwave radiometer, with one channel at 150 GHz and three channels at 183 GHz. It was very similar in design to the AMSU-B instrument,...
. The MetOp AMSU-A similarly works with HIRS, IASI, and MHS. MHS and HSB are variants on AMSU-B.
- Heritage: Microwave Sounding Unit (MSU)
- Swath: 1650 km
- Footprint size: for a nominal spacecraft altitude of 833 km, 48 km at nadir (AMSU-A), 16 km at nadir (AMSU-B).
- Mass: 100 kg
- Duty cycle: 100 %
- Power: 125 W
- Data Rate: 3.2 kbit/s
- Max scan angle: ±49.5°
- Instrument Instantaneous FOV: 3.3° (AMSU-A) 1.1° (AMSU-B)
Table 1 Radiometric characteristics of the AMSU-A (from 3,5).
| Channel Number | Frequency (GHz) |
Polarization (at 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... ) |
Number of Bands |
Instrument Sensitivity NEDT (K Kelvin The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all... ) |
Primary Function |
| 1 | 23.8 | vertical | 1 | 0.30 | Water Vapor Burden |
| 2 | 31.4 | vertical | 1 | 0.30 | Water Vapor Burden |
| 3 | 50.3 | vertical | 1 | 0.40 | Water Vapor Burden |
| 4 | 52.8 | vertical | 1 | 0.25 | Water Vapor Burden |
| 5 | 53.596 ± 0.115 | horizontal | 2 | 0.25 | Tropospheric Temperature |
| 6 | 54.4 | horizontal | 1 | 0.25 | Tropospheric Temperature |
| 7 | 54.94 | vertical | 1 | 0.25 | Tropospheric Temperature |
| 8 | 55.5 | horizontal | 1 | 0.25 | Tropospheric Temperature |
| 9 | 57.290 | horizontal | 1 | 0.25 | Stratospheric Temperature |
| 10 | 57.290 ± 0.217 | horizontal | 2 | 0.40 | Stratospheric Temperature |
| 11 | 57.290 ± 0.3222 ± 0.048 | horizontal | 4 | 0.40 | Stratospheric Temperature |
| 12 | 57.290 ± 0.3222 ± 0.022 | horizontal | 4 | 0.60 | Stratospheric Temperature |
| 13 | 57.290 ± 0.3222 ± 0.010 | horizontal | 4 | 0.80 | Stratospheric Temperature |
| 14 | 57.290 ± 0.3222 ± 0.0045 | horizontal | 4 | 1.20 | Stratospheric Temperature |
| 15 | 89.0 | vertical | 1 | 0.50 | Cloud Top/Snow |
Table 2 Radiometric characteristics of the AMSU-B (from 4).
| Channel Number | Frequency (GHz) |
Polarization (at nadir) |
Number of bands |
Instrument Sensitivity NEDT (K Kelvin The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all... ) |
| 16 | 89.9 ± 0.9 | vertical | 2 | 0.37 |
| 17 | 150 ± 0.9 | vertical | 2 | 0.84 |
| 18 | 183.31 ± 1.00 | vertical | 2 | 1.06 |
| 19 | 183.31 ± 3.00 | vertical | 2 | 0.70 |
| 20 | 183.31 ± 7.00 | vertical | 2 | 0.60 |
External links
- Data processing for AMSU at Colorado State
- AMSU-A datasheet from NASA's EOS Aqua project
- NOAA KLM User's guide AMSU-A
- NOAA KLM User's guide AMSU-B
- NASA's AMSU-A Instrument guide
- Data from NASA's AMSU-A and companion instruments at NASA's Goddard Spaceflight Center
- Data from AMSU and associated TOVS and ATOVS instruments at NOAA's CLASS