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== Advanced Microwave Sounding Unit ==

The Advanced [[microwave|Microwave]] [[sounding|Sounding]] Unit (AMSU) instrument suite consists of AMSU-A and AMSU-B. The primary function of the AMSUs is to obtain [[temperature]] and [[water vapor]] in the [[troposphere]] and [[stratosphere]]. The first AMSU was launched on 13 May 1998, on board the National Oceanic and Atmospheric Administration's (NOAA's) ''NOAA-15'' [[Polar-orbiting operational environmental satellite|Polar-Orbiting Operational Environmental Satellite]] ([[Poes|POES]]), and the last one was launch on ''NOAA-19'' (6 February 2009). For actual characteristics of each AMSU on ''NOAA-15'' through ''NOAA-19'', see the NOAA KLM Users Guide (section 3.3, 3.4 and Appendix D).<br/>

AMSU-A is a 15-channel microwave sounder designed primarily to obtain temperature profiles in the troposphere and stratosphere. Each AMSU-A instrument is composed of two separate units: AMSU-A2 with 2 channels at 23.8 and 31.4 GHz and AMSU-A1 with 12 channels in the range of 50.3–57.3 GHz plus 1 channel at 89.0 GHz. AMSU-A1 has a set of 12 [[oxygen]] band channels (3–14) for retrieving the atmospheric temperature profile from the Earth's surface to about 50 km in [[altitude]]. [[Precipitation]], [[sea ice]], [[snow cover]], surface [[emissivity]], atmospheric liquid [[water]], and total [[precipitable water]] are derived primarily from three window channels (23.8 and 31.4 GHz from AMSU-A2 and 89.0 GHz from AMSU-A1).<br/>

AMSU-B, later called the Microwave [[humidity|Humidity]] Sounder (MHS) measures five microwave channels and accompanies AMSU-A: one channel in the 89-GHz "window" channel, one channel at 150 GHz, and remaining three channels around the 183-GHz water vapor line. The primary function of AMSU-B (MHS) is to obtain the water vapor profile in the troposphere and lower stratosphere.<br/> 

<p>''Term edited 10 August 2021.''</p>