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The VIIRS instrument onboard the NOAA-21 spacecraft has successfully operated since its launch on November 18, 2022. A panchromatic channel in 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. The on-orbit calibration performance is monitored via the gain trending of low-gainstage (LGS), gain ratios of mid-gain-stage (MGS) to LGS, and high-gain-stage (HGS) to MGS, as well as dark offsets in all modes, detectors and HAM sides. Contamination of DNB images due to straylight has been observed in previous VIIRS builds. Data from monthly new moon observations have been used to estimate the straylight impact such that a look-up-table (LUT) has been built each month to correct the contaminated images. In this paper, the calibration algorithm and performance of NOAA-21 VIIRS DNB have been presented, together with the comparisons to previous VIIRS instruments onboard the S-NPP and NOAA-20 spacecraft.
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