Inter-channel uniformity of a microwave sounder in space
Abstract. We analyzed intrusions of the Moon in the deep space view of the Advanced
Microwave Sounding Unit-B on the NOAA-16 satellite and found no significant
discrepancies in the signals from the different sounding channels between
2001 and 2008. However, earlier investigations had detected biases of up to
10 K, by using simultaneous nadir overpasses of NOAA-16 with other satellites.
These discrepancies in the observations of Earth scenes cannot be due to
non-linearity of the receiver or contamination of the deep space view without
affecting the signal from the Moon as well. As neither major anomalies of the
on-board calibration target nor the local oscillator were present,
we consider radio frequency interference in combination with a strongly
decreasing gain the most obvious reason for the degrading photometric
stability. By means of the chosen example we demonstrate the usefulness of
the Moon for investigations of the performance of microwave sounders in
flight.