On-Orbit Absolute Calibration of the Advanced Technology Microwave Sounder

The Advanced Technology Microwave Sounder (ATMS) onboard SNPP and NOAA-20 profiles atmospheric temperature and moisture in all-weather conditions, and supports continuing advances in numerical weather prediction (NWP) for improved short- to medium-range weather forecast skills. Since the ATMS onboard NOAA-20/SNPP are identical, it is critical to identify the calibration difference between these two instruments. To investigate the instrument on-orbit radiometric and geometric calibration performance, series of spacecraft and instrument active/passive maneuvers, such as roll maneuver, pitch maneuver, lunar intrusion, and environmental characterization were carried out when ATMS was activated after launch. By combined using the on-orbit derived instrument parameters and ground test datasets, a comprehensive investigation for instrument calibration error budget was carried out and an on-orbit absolute calibration algorithm can be developed for ATMS. Evaluation results show that by using the proposed algorithm, calibration error for both NPP and N20 ATMS can be within 0.5K and calibration difference between the two instrument can be controlled below 0.2K.