NOAA-20 VIIRS operational radiometric calibration updates for the reflective solar bands Earth Observing Systems XXVII

The Visible Infrared Imaging Radiometer Suite (VIIRS) was successfully launched on November 18, 2017, onboard the National Oceanic and Atmospheric Administration-20 (NOAA-20) satellite. With its activation on November 28, 2017, VIIRS started producing Solar Diffuser (SD) observations and performing on-orbit radiometric calibration for accurate Sensor Data Records (SDRs). After the initial adjustment of the calibration coefficients called F-PREDICTED LUTs, the F-PREDICTED LUT has been set to a constant level for each detector in the Reflective Solar Bands (RSB) after April of 2018 because no noticeable degradation has been observed. Meanwhile, the NOAA VIIRS SDR team has been checking the validity of the F-PREDICTED LUT by comparing with the lunar calibration coefficients (F-factors), Deep Convective Cloud (DCC) trends. Recently, small but meaningful upward trends (indicative of responsivity degradation) were observed in some RSB F-factors and the NOAA-20 VIIRS F-PREDICTED LUT was updated to replace the current constant F-factors for M1-M6 and I1. The changes were based on the lunar calibration trends that were validated by the daily and monthly time series of DCC observations. The changes will smoothly mitigate the observed degradation in two years to provide the best radiometric calibration for the current VIIRS SDR products. By monitoring the lunar and DCC trends frequently, a follow-on update is expected when there is a significant long-term trend change between current F-PREDICTE LUT and lunar or DCC trends.