Once on orbit, the bidirectional reflectance distribution function (BRDF) of the solar diffuser (SD) of the Visible Infrared Imaging Radiometer Suite (VIIRS) aboard the NOAA-20 satellite changes over time. The change factor is determined by an onboard solar diffuser stability monitor (SDSM). However, the design band central wavelengths (412 to 926 nm) of the SDSM detectors do not cover the VIIRS short wave infrared (SWIR) bands which have band central wavelengths from 1.238 to 2.257 μm. Although it is known that the SD BRDF changes at a much slower rate in time over longer wavelengths, the change over some of the SWIR bands’ central wavelengths may still be large enough to be ignored. To determine the NOAA-20 VIIRS SD BRDF change factor over the SWIR band wavelength region, we use the solar photon wavelength power law approach that has been applied to the VIIRS instrument onboard the Suomi National Polar-orbiting Partnership satellite. In this work, we show the results for the NOAA-20 VIIRS.
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