The advanced

microwave sounding unit The microwave sounding unit (MSU) was the predecessor to the Advanced Microwave Sounding Unit (AMSU). The MSU was first launched aboard the TIROS-N satellite in late 1978 and provided global coverage (from Pole to Pole). It carries a 4-channel micr ...

(AMSU) is a multi-channel

microwave radiometer A microwave radiometer (MWR) is a radiometer that measures energy emitted at one millimeter-to-metre wavelengths (frequencies of 0.3–300 GHz) known as microwaves. Microwave radiometers are very sensitive receivers designed to measure thermally ...

installed on meteorological satellites. The instrument examines several bands of microwave radiation from the atmosphere to perform

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, o ...

of temperature and moisture levels.

Products

Level-1 radiance data are calibrated

brightness temperature Brightness temperature or radiance temperature is a measure of the intensity of electromagnetic energy coming from a source. In particular, it is the temperature at which a black body would have to be in order to duplicate the observed intensity ...

s. Level-2 geophysical data from AMSU include: * Temperature profile from 3

mbar The bar is a metric unit of pressure defined as 100,000 Pa (100 kPa), though not part of the International System of Units (SI). A pressure of 1 bar is slightly less than the current average atmospheric pressure on Earth at sea ...

(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 prediction Numerical weather prediction (NWP) uses mathematical models of the atmosphere and oceans to weather forecasting, predict the weather based on current weather conditions. Though first attempted in the 1920s, it was not until the advent of comput ...

(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 is the long-term weather pattern in a region, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteoro ...

History

AMSU-A + AMSU-B have flown together on the 3 NOAA KLM satellites: NOAA-15 (NOAA K), launched May 13, 1998;

NOAA-16 NOAA-16, also known as NOAA-L before launch, was an operational, polar orbiting, weather satellite series (NOAA K-N) operated by the National Environmental Satellite Service (NESS) of the National Oceanic and Atmospheric Administration (NOAA). N ...

(NOAA L), launched September 21, 2000; and

NOAA-17 NOAA-17, also known as NOAA-M before launch, was an operational, polar orbiting, weather satellite series (NOAA K-N) operated by the National Environmental Satellite Service (NESS) of the National Oceanic and Atmospheric Administration (NOAA). N ...

(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 The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

Aqua Earth science satellite and the

EUMETSAT The European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) is an intergovernmental organisation created through an international convention agreed by a current total of 30 European Member States. EUMETSAT's primary ...

MetOp MetOp (Meteorological Operational satellite) is a series of three polar-orbiting meteorological satellites developed by the European Space Agency (ESA) and operated by the European Organisation for the Exploitation of Meteorological Satellites ...

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 The microwave sounding unit (MSU) was the predecessor to the Advanced Microwave Sounding Unit (AMSU). The MSU was first launched aboard the TIROS-N satellite in late 1978 and provided global coverage (from Pole to Pole). It carries a 4-channel micr ...

(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 the Advanced Technology Microwave Sounder (ATMS), first flown on Suomi-NPP in 2011 and now standard equipment on the JPSS series of satellites, the first of which,

NOAA-20 NOAA-20, designated JPSS-1 prior to launch, is the first of the United States National Oceanic and Atmospheric Administration's latest generation of U.S. polar-orbiting, non-geosynchronous, environmental satellites called the Joint Polar Sate ...

, launched in 2017. AMSUs were manufactured by

Aerojet Aerojet was an American rocket and missile propulsion manufacturer based primarily in Rancho Cordova, California, with divisions in Redmond, Washington, Orange and Gainesville in Virginia, and Camden, Arkansas. Aerojet was owned by GenCorp, ...

Corporation in

Azusa, California Azusa ( Tongva: ''Azuksa'', meaning "skunk") is a city in the San Gabriel Valley region of Los Angeles County, California, United States, at the foot of the San Gabriel Mountains and located east of downtown Los Angeles. Its population wa ...

. This organization is now part of Northrop Grumman Electronic Systems.

Observation geometry

It is preferred that AMSUs always situated on polar-orbiting satellites in

Sun-synchronous orbit A Sun-synchronous orbit (SSO), also called a heliosynchronous orbit, is a nearly polar orbit around a planet, in which the satellite passes over any given point of the planet's surface at the same local mean solar time. More technically, it is ...

s, however NOAA-15 to NOAA-19 all had drifting LTANs. In the case of Metops and EOS Aqua 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 is a calculation of the passage of time based on the position of the Sun in the sky. The fundamental unit of solar time is the day, based on the synodic rotation period. Traditionally, there are three types of time reckoning based ...

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 14 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

GHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or Cycle per second, cycle) per second. The hertz is an SI derived unit whose formal expression in ter ...

, 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 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 ...

) and to provide a cloud-filtering capability for

tropospheric The troposphere is the lowest layer of the atmosphere of Earth. It contains 80% of the total mass of the planetary atmosphere and 99% of the total mass of water vapor and aerosols, and is where most weather phenomena occur. From the planetary s ...

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. *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). Table 2 Radiometric characteristics of the AMSU-B (from 4). {, border="1" width="100%" cellpadding="2" cellspacing="2" , - , valign="top" , Channel Number , valign="top" , Frequency
(GHz)
, valign="top" , Polarization
(at nadir)
, valign="top" , Number
of bands
, valign="top" , Instrument Sensitivity
NEDT ( K)
, - , 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

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
Atmospheric sounding satellite sensors