The Advanced Microwave Sounding Unit-A (AMSU-A) is designed to measure global atmospheric temperature profiles.
It provides information on atmospheric water in all of its forms (with the exception of small ice particles, which are transparent at microwave frequencies). AMSU-A provides information even in cloudy conditions.
What is AMSU-A?
AMSU-A is a multi-channel microwave radiometer which measure scene radiances in 15 discreet frequency channels (23-90 GHz).
At each channel frequency, the antenna beamwidth is a constant 3.3 degrees (at the half power point).
Thirty consecutive scene resolution cells are sampled in a stepped-scan fashion every eight seconds, each scan covering about 50 degrees on either side of the subsatellite path.
These scan patterns and geometric resolution translate to a 48 km diameter cell at nadir and a 2,074 km swath width from the 837 km nominal orbital altitude.
AMSU-A uses oxygen absorption bands/lines for atmospheric temperature sounding. Window channels at 23.8, 31.4 and 89 GHz provide information on surface temperature and emissivity.
Hardware for the two lowest frequencies is located in one module (Fig 2), with the remaining 13 frequencies being accommodated in the second module (AMSU-A1).
This arrangement puts the two lower atmospheric moisture viewing channels into one module and the oxygen absorption channels into a second common module, in order to ensure commonality of viewing angle (independent of any module and/or spacecraft misalignment due to structural or thermal distortions).
The AMSU-A2 module has a single antenna assembly, providing data for channels 1 and 2. AMSU-A1 has two separate antenna assemblies: AMSU-A1.1 provides data for channels 6,7 and 9-15 and AMSU-A1.2 provides data for channels 3, 4, 5 and 8.
AMSU-A is part of the ATOVS package, together with MHS and HIRS. AMSU-A scanning is synchronized with MHS and IASI scanning. The instrument is manufactured by Northrop Grumman (previously Aerojet), Azusa, California under contract to NASA. For more in-depth information, see the ATOVS Level 1b Product Guide.