NOAA-21 VIIRS Day-Night Band On-orbit Calibration and Performance in Early Mission

The NOAA-21 VIIRS instrument has successfully operated since its launch on November 10, 2022. A panchromatic channel onboard VIIRS, referred to as the day-night band (DNB), was designed with multiple gain stages resulting in a large dynamic range and high sensitivity such that its detectors can make observations during both spacecraft day and spacecraft night. An onboard solar diffuser (SD) panel provides a well-understood calibration source for the low gain stage (LGS). While there is no direct, onboard calibration source for the mid gain stage (MGS) or high gain stages (HGS), measurements of the SD during times of indirect solar illumination can provide relative gain ratios between the LGS/MGS and MGS/HGS. Results from an early mission pitch maneuver and regular new moon observations are used in combination with onboard calibrator trends to determine the DNB dark offset (DN0) levels. In this paper, we present details for the NOAA-21 VIIRS DNB on-orbit calibration and highlight its early mission performance. Calibration coefficient look up tables (LUTs) are calculated by the NASA VIIRS characterization support team (VCST) for the latest NASA Level 1B (L1B) Collection 1 products. DNB straylight contamination has been observed to differing degrees for earlier VIIRS instruments currently on both the SNPP and NOAA-20 spacecraft. We discuss the impact of straylight on the NOAA-21 VIIRS DNB in comparison to the previous instruments and the performance of our current straylight correction for L1B radiance products.