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On-orbit characterization of the VIIRS solar diffuser and attenuation screens for NOAA-20 using yaw measurements.

The follow-up visible infrared imaging radiometer suite (VIIRS) housed in the NOAA-20 satellite and the first of four in the NOAA Joint Polar Satellite System satellite series, was launched on 18 November 2017. The on-orbit satellite yaw maneuver operation was carried out on 25-26 January 2018 over 15 scheduled orbits to obtain responses of the reflective solar bands (RSBs) and the solar diffuser stability monitor (SDSM) over a specified angular range. This paper presents a comprehensive analysis of the yaw measurements that characterizes the three required input functions for the standard on-orbit RSB calibration pipeline. The characterization functions of the product of the bidirectional reflectance factors (BRFs) of the solar diffuser (SD) with the vignetting function (VF) of the SD screen (SDS), dubbed the BRF-VF-products (BVPs), are derived for the two required outgoing directions from the SD, one set for the RSB BVPs from the SD to the rotation telescope assembly that directs light to the RSBs, and another set for the SDSM BVPs for the outgoing direction from the SD to the SDSM. The VFs for the attenuation screen placed in front of the Sun-view port, the Sun-view screen (SVS), are analyzed as a set of standalone functions to characterize the direct solar illumination reaching the SDSM through the SVS, but the complexity of their non-smooth two-dimensional dependence requires an additional direct treatment in the derivation of the degradation of the SD, the H-factors. The results for the RSB BVPs, SDSM BVPs, and the SVS VFs are presented and discussed, and further applied to derive the early-mission performance of H-factors and the RSB calibration coefficients, or F-factors. The overall results of the H-factors and F-factors showing smooth trends with negligible residuals indicate that the derived BVP functions and the SVS VFs have been accurately characterized or treated, and are ready for use for the standard on-orbit RSB calibration of NOAA-20 VIIRS.