The Advanced Microwave Sounding Unit-A (AMSU-A) is designed to measure global atmospheric temperature profiles.
Last Updated
08 December 2022
Published on
05 May 2020
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 (23-90GHz).
At each channel frequency, the antenna beamwidth is a constant 3.3 degrees (at the half power point). AMSU-A is part of the ATOVS package, together with MHS and HIRS. AMSU-A scanning is synchronized with MHS and IASI scanning.
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.
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.
Hardware for the two lowest frequencies is located in one module (Figure 1), 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.
Figure 1: AMSU-A channels
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.
Parameter
Details
Scan rate
8 secs
Scan type
Stop and stare
Pixel IFOV (3dB beamwidth)
3.3°
IFOV size at nadir
48 km
Sampling at nadir
48 km
Earth view pixels/scan
30
Swath
± 48.33°
Swath width
± 1037 km
Frequency range
23 to 89 GHz
Lifetime
Three years
Power
A1: 75 W, A2: 24 W
Size
A1: 736 mm x 413 mm x 608 mm, A2: 635 mm x 744 mm x 688 mm
Mass
A1: 54 kg, A2: 50 kg
Data rate
A1: 2.1 kbps, A2: 1.1 kbps
Primary mission objectives:
Specific humidity
Secondary mission objectives:
Cloud ice Total Column
Cloud liquid water (CLW) total column
Integrated Water Vapour (IWV)
Precipitation intensity at surface (liquid or solid)