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 one 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.