NOAA-21 VIIRS Thermal Emissive Bands Early On-Orbit Calibration Performance and Improvements

The Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the National Oceanic and Atmospheric Administration-21 (NOAA-21) satellite was launch on November 10, 2022, following the successful operations of the VIIRS onboard the Suomi National Polar-orbiting Partnership (S-NPP) and NOAA-20 satellites. This article presents NOAA-21 VIIRS thermal emissive bands (TEBs) early on-orbit calibration performance, including instrument temperature telemetry trending, TEB gains, noise, and calibration stability as well as biases in the NOAA operational sensor data records (SDR). Different from S-NPP and NOAA-20, NOAA-21 VIIRS TEBs have experienced distinct on-orbit gain changes during its early mission, caused by detector responsivity degradations, mid-mission outgassing (MMOG), and the cold focal plane assembly setpoint temperature switch. The calibration stability and biases of NOAA-21 VIIRS TEB SDRs were analyzed by intercomparing with co-located Cross-Track Infrared Sounder (CrIS) observed and gap-filled spectra. NOAA-21 TEB SDRs have been stable, except for small changes caused by known VIIRS or CrIS instrument setting or calibration updates. VIIRS longwave infrared (LWIR) bands agree with CrIS within 0.1 K; M13 agrees with CrIS ~0.13 K. Calibration parameters derived from the spacecraft pitch maneuver data were applied for the first time in the operational processing, and LWIR scan angle and scene temperature-dependent biases were effectively reduced after that update. Similar to S-NPP and NOAA-20 VIIRS, NOAA-21 VIIRS TEBs also exhibit calibration anomalies during the blackbody warm-up/cool-down (WUCD) tests. NOAA-21 WUCD bias correction coefficients were developed and deployed to the operations for supporting sea surface temperature (SST) applications.