Preliminary assessment of the NOAA-21 VIIRS on-orbit reflective solar band calibration and performance

Abstract

On November 10, 2022, the NOAA-21 (also known as Joint Polar Satellite System (JPSS)-2) Visible Infrared Imaging Radiometer Suite (VIIRS) was successfully launched and operated on-orbit. The NOAA-21 VIIRS is the third VIIRS instrument in the series, following S-NPP and NOAA-20, providing 22 spectral bands that cover a spectral range from 0. 402 µm to 12.5 µm. From the intensive Post Launch Tests (PLTs), the NOAA-21 VIIRS Sensor Data Record (SDR) achieved beta maturity status on Feb. 23, 2023 and is expected to achieve provisional and validated maturity in the next few months, ensuring the performance requirements are met and data are of high quality with on-orbit calibration.The accuracy of the current NOAA-21 VIIRS Reflective Solar Band (RSB) calibration was limited by in the Solar Diffuser (SD) degradation estimates, which proportionally affect the accuracy of the on-orbit RSB calibration. To achieve the beta maturity status, the SD degradation was omitted from the initial radiometric response analyses, and calculated solar calibration scaling coefficients (F-factors) were extrapolated to the start of the on-orbit operations that marked the onset of the SD degradation.To mitigate the unexpected SD reflectance variability, a series of yaw maneuvers will be performed as a part of the PLTs during the Intensive Calibration and Validation (ICV) phase. In addition to the yaw points, on-orbit Solar Diffuser Stability Monitor data sets will fill the intermediate angles between the yaw angles. The updated estimates of the SD degradation (H-factors) will be applied in the SD F-factor calculations. Finally, the improved SD F-factors will be compared and validated with vicarious calibration results, such as lunar F-factors. This paper will evaluate the impacts of SD-based calibration updates for NOAA-21 RSBs through assessing the radiometric biases of NOAA-21 VIIRS RSBs relative to NOAA-20 ensuring the radiometric accuracy of the NOAA-21 SDR products.