Calibration of the AIRS microwave instruments

Aqua carries three microwave radiometers that form an integral part of the Atmospheric Infrared Souding (AIRS) sounding suite. Two Advanced Microwave Sounding. Unit-A modules, one operating with two channels in the 23-31-GHz range and on e operating with 12-channels in the 50-60-GHz range and one channel at 89 GHz, provide all-weather temperature soundings and cloud information. The Humidity Sounder for Brazil operates with four channels-in the 150-190-GHz range and provides all-weather humidity and cloud soundings. All are crosstrack scanners, as is AIRS. While there are significant differences between these three instruments, they are sufficiently alike that a common approach can be used to calibrate them. We describe the instruments and their heritage, the onboard calibration system, and the ground-based calibration processing.