Advanced Microwave Sounding Unit
2194707
219191167
2008-06-14T00:27:47Z
Neutrality
68411
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.
[[Image:Isidore flooding diff.jpg|thumb|right|Flooding from Hurricane Isidore shown by AMSU channel 2]]
==Products==
Level-1 radiance data are calibrated [[brightness temperature]]s.
Level-2 geophysical data from AMSU include:
* Temperature profile from 3 [[Bar (unit)|mbar]] (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]] (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]].
== 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 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 (satellite)| Aqua]] Earth science satellite and the [[European Organisation for the Exploitation of Meteorological Satellites| EUMETSAT]] [[MetOp]] series. On these spacecraft, AMSU-B is replaced by similar microwave humidity sounders: [[Humidity Sounder for Brazil|HSB]] for Aqua and [[Microwave humidity sounder|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]].
== Observation geometry ==
AMSUs are always situated on polar-orbiting satellites in [[sun-synchronous orbit]]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.
== Instrument characteristics ==
The AMSU has two sub-instruments, AMSU-A and AMSU-B. AMSU-A has 15 channels between 23.8 and 89 [[GHz]], and is used primarily for measuring atmospheric temperatures (known as "temperature sounding"). It has a ground [[angular resolution|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 [[Atmospheric Infrared Sounder|AIRS]] and [[Humidity Sounder for Brazil|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
*Spatial resolution: 45 km horizontal at nadir (AMSU-A), 15 km at nadir (AMSU-B)
*Mass: 100 kg
*Duty cycle: 100 %
*Power: 125 W
*Data Rate: 3.2 kbit/s
*Field of View (FOV): ±49.5°
*Instrument Instantaneous FOV: 3.3° (AMSU-A) 1.1° (AMSU-B)
'''Table 1 Radiometric characteristics of the AMSU-A (from [[Advanced Microwave Sounding Unit#References|3,5]]). '''
{| border="1" width="100%" cellpadding="2" cellspacing="2"
|-
| valign="top" | Channel Number
| valign="top" | Frequency<br>
(GHz)<br>
| valign="top" | Polarization<br>
(at [[nadir]])<br>
| valign="top" | Number<br>
of Bands<br>
| valign="top" | Instrument Sensitivity <br>
[[NEDT]] ([[Kelvin|K]])<br>
| valign="top" | Primary Function <br>
|-
| 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 [[Advanced Microwave Sounding Unit#References|4]]). '''
{| border="1" width="100%" cellpadding="2" cellspacing="2"
|-
| valign="top" | Channel Number
| valign="top" | Frequency<br>
(GHz)<br>
| valign="top" | Polarization<br>
(at nadir)<br>
| valign="top" | Number<br>
of bands<br>
| valign="top" | Instrument Sensitivity <br>
[[NEDT]] ([[Kelvin|K]])<br>
|-
| 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==
* [http://amsu.cira.colostate.edu Data processing for AMSU at Colorado State]
* [http://www.aqua.nasa.gov/about/instrument_amsu.php AMSU-A datasheet from NASA's EOS Aqua project]
* [http://www2.ncdc.noaa.gov/docs/klm/html/c3/sec3-3.htm NOAA KLM User's guide AMSU-A]
* [http://www2.ncdc.noaa.gov/docs/klm/html/c3/sec3-4.htm NOAA KLM User's guide AMSU-B]
* [http://disc.gsfc.nasa.gov/AIRS/documentation/amsu_instrument_guide.shtml NASA's AMSU-A Instrument guide]
* [http://disc.gsfc.nasa.gov/AIRS/data_products.shtml Data from NASA's AMSU-A and companion instruments at NASA's Goddard Spaceflight Center]
* [http://www.class.noaa.gov/saa/products/search?sub_id=0&datatype_family=TOVS&submit.x=19&submit.y=13 Data from AMSU and associated TOVS and ATOVS instruments at NOAA's CLASS]
[[Category:Spacecraft instruments]]
[[Category:Satellite meteorology and remote sensing]]
[[Category:Earth observation satellites]]