Aquarius L-band Radiometers Calibration Using Cold Sky Observations

An important element in the calibration plan for the Aquarius radiometers is to look at the cold sky. This involves rotating the satellite 180° from its nominal Earth viewing configuration to point the main beams at the celestial sky. At L-band, the cold sky provides a stable, well-characterized scene to be used as a calibration reference. This paper describes the cold sky calibration for Aquarius and how it is used as part of the absolute calibration. Cold sky observations helped establish the radiometer bias, by correcting for an error in the spillover lobe of the antenna pattern, and monitor the long-term radiometer drift.