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Wikipedia : Advanced microwave sounding unit
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AMSUs are always situated on polar-orbiting satellites in sun-synchronous orbits.
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.
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