The AMSR-E is a conically
scanning total power passive microwave radiometer sensing microwave radiation
(brightness temperatures) at 12 channels and 6 frequencies ranging from
6.9 to 89.0 GHz. Horizontally and vertically polarized radiation are measured
separately at each frequency. There are 2 separate horns at 89 GHz, one
being slightly offset from the centerline of the feedhorn array. (As
of 25 October 2004, there are no data from the 89 GHz horn A. The science
algorithms have been modified to take this into account).
A cold load reflector and a warm load are mounted on the transfer assembly shaft and do not rotate with the drum assembly. They are positioned off axis such that they pass between the feedhorn array and the parabolic reflector, occulting it once each scan. The cold load reflector reflects cold sky radiation into the feedhorn array thus serving, along with the warm load, as calibration references for the AMSR-E. Calibration of the radiometers is essential for collection of useful data. Corrections for spillover and antenna pattern effects are incorporated in the data processing algorithms. For more information, see Radiometer Calibration.
The AMSR-E rotates continuously about an axis parallel to the local spacecraft vertical at 40 revolutions per minute (rpm). At an altitude of 705 km, it measures the upwelling scene brightness temperatures over an angular sector of ±61 degrees about the sub-satellite track, resulting in a swath width of 1445 km.
During a period of 1.5 seconds the spacecraft sub-satellite point travels 10 km. Even though the instantaneous field-of-view for each channel is different, active scene measurements are recorded at equal intervals of 10 km (5 km for the 89 GHz channels) along the scan. The half cone angle at which the reflector is fixed is 47.4° which results in an Earth incidence angle of 55.0°. Table 1 lists the pertinent performance characteristics.
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