LAUSR

On February 15 and 16, 2012, a series of yaw maneuvers was performed on the Suomi National Polar-Orbiting Partnership (S-NPP) spacecraft for Visible Infrared Imaging Radiometer Suite (VIIRS) to characterize screen transmission functions and Bidirectional Reflectance Distribution Functions (BRDFs). For accurate time-dependent calibration coefficient (or F-factor) calculation in the Reflective Solar Bands (RSBs), the Solar Diffuser (SD) and SD Stability Monitor (SDSM) screen transmission functions are measured using the on-orbit yaw maneuver data with three screen transmission functions. The SD screen transmittance function coupled with the SD BRDF ( $\tau _{\mathrm {SD}}$ BRDF) is updated and then the SDSM Sun and SDSM SD BRDF functions are updated. The SDSM solar and SD view functions are used in the SD degradation estimation, which affects the VIIRS view of the SD BRDF through the rotating telescope over time. The prelaunch measurements of these transmission or BRDF functions were too coarse to capture the small features of the transmission functions. There have been several efforts to derive better models but the annual oscillations in the F-factors remained to be a major issue. To mitigate these F-factor oscillations, the yaw maneuver data are reanalyzed to derive the transmittance and BRDF functions. This paper shows that the annual oscillations are caused by the imperfect SDSM Sun screen transmittance and SDSM SD BRDF functions. When the newly calculated SDSM SD BRDF and Sun transmittance lookup tables (LUTs) are applied, the annual oscillations in the H-and F-factors are significantly reduced, especially in the bands M1–M4.