The third Earth observing Visible Infrared Imaging Radiometer Suite (VIIRS) is on the recently launched NOAA-21 satellite. Like its predecessors on the SNPP and NOAA-20 satellites, the VIIRS provides daily global geometrically and radiometrically calibrated observations via its 22 spectral bands from 0.41 to 12 mm. VIIRS has 14 reflective solar bands (RSBs), covering wavelengths from 0.41 to 2.25 m. On orbit, the RSBs are radiometrically calibrated through a sunlit solar diffuser (SD). The on-orbit change of the SD’s bidirectional reflectance distribution function (BRDF) is determined by using the onboard solar diffuser stability monitor (SDSM). An SDSM screen and an SD screen, both with holes to let sunlight pass through, are involved in the calibration. The SDSM screen relative transmittance and the products of the SD screen transmittance and the SD BRDF for the SDSM and the telescope SD views were measured prelaunch. But large errors are associated with the prelaunch SDSM screen function. As a result, the SDSM measured SD BRDF onorbit change factor versus time data points have large unrealistic undulations. To improve the screen functions, satellite yaw maneuvers were performed and the calibration data from the yaw maneuver orbits were used to rederive the screen functions. Here, we apply a previously developed methodology with a slight improvement to further refine the screen functions, using the calibration data not only from the yaw maneuver orbits but also from a small portion of the regular orbits. With the updated screen functions, the SDSM determined SD BRDF on-orbit change factors, as well as the retrieved NOAA-21 VIIRS RSB radiometric gains, are much smoother functions of time.

(2024) Published by SPIE. Downloading of the abstract is permitted for personal use only.

Ning Lei and Xiaoxiong Xiong, "NOAA-21 VIIRS screen transmittance functions derived from on-orbit calibration data," Proc. SPIE 13143, Earth Observing Systems XXIX, 131430Q (Presented at Optical Engineering + Applications: August 21, 2024; Published: 3 October 2024); https://doi.org/10.1117/12.3027458.