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&nbsp;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&nbsp;km, so the next scan will be 45&nbsp;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&nbsp;[[GHz]], and is used primarily for measuring atmospheric temperatures (known as "temperature sounding"). It has a ground [[angular resolution|resolution]] near nadir of 45&nbsp;km. AMSU-B, with five channels between 89 and 183.3&nbsp;GHz, has a spatial resolution near nadir of 15&nbsp;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&nbsp;km *Spatial resolution: 45&nbsp;km horizontal at nadir (AMSU-A), 15&nbsp;km at nadir (AMSU-B) *Mass: 100&nbsp;kg *Duty cycle: 100&nbsp;% *Power: 125&nbsp;W *Data Rate: 3.2&nbsp;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]]