Effect of the SDSM detector relative spectral response in determining the degradation coefficient of the SNPP VIIRS Solar Diffuser reflectance

The Visible/Infrared Imager Radiometer Suite (VIIRS) instrument aboard the Suomi National Polar-orbiting Partnership (SNPP) satellite performs its radiometric calibration in the reflective solar bands (RSB) wavelength region primarily through observing the sunlight scattered from the onboard Solar Diffuser (SD). The degradation (over time) of the SD reflectance is determined by the onboard Solar Diffuser Stability Monitor (SDSM). The SDSM detector relative spectral response (RSR) over the out-of-band (OOB) wavelength region leads to a non-negligible bias to the originally determined SD degradation coefficient over wavelengths from 412 nm to 488 nm. In this Proceeding, we consider the out-of-band contribution to determine the bias. Our computation shows that the bias to the degradation coefficient is larger at a shorter wavelength and increases with time. On the 564th day after launch (similar to orbit 8000), at a wavelength of 412 nm, the bias (OOB-corrected - not-OOB-corrected) has a mean of -0.021, and at a wavelength of 445 nm, the bias has a mean of -0.009.