NOAA-21 VIIRS thermal emissive bands on-orbit calibration and performance in early mission

The Visible Infrared Imaging Radiometer Suite (VIIRS) instrument is currently operating onboard the NOAA-21 (or JPSS-2) satellite, which was launched successfully from the Vandenberg Space Force Base in California on November 10, 2022. This is the third VIIRS instrument flying on a series of Joint Polar Satellite System (JPSS) satellites, including S-NPP and NOAA-20 (or JPSS-1), along with other Earth observing instruments on board. The measurements collected by VIIRS are used for weather forecasting and environmental science research. Among 22 spectral bands of VIIRS, there are seven mid- and long-wave infrared Thermal Emissive Bands (TEB) ranging from 3.7 to 12.2 microns at two different spatial resolutions; imagery resolution bands (I-bands) I4 and I5 are 375 m per pixel at nadir, and moderate resolution bands (M-bands) M12 - M16 are 750 m. The VIIRS TEB detectors are calibrated by an On-Board Calibrator (OBC) blackbody (BB) at controlled temperatures with a deep Space View (SV) for background signal measurement. Prior to launch, the TEB went through rigorous pre-launch calibration and characterization tests in ambient and thermal vacuum environments. During the initial post-launch testing (PLT) period, a comprehensive set of tests and spacecraft maneuvers were performed to ensure the health of the satellite and all sensors. The PLT results help the understanding of instrument response and performance, and to bridge the calibrations between pre-launch and post-launch for traceability. This paper provides an overview of NOAA-21 VIIRS TEB PLTs with their results and follow-on on-orbit performance. Comparisons with NOAA-20 and S-NPP VIIRS TEB are also made in various categories including noise characterization, blackbody stability, and detectors response.