NPP VIIRS early on-orbit solar diffuser degradation results

The Visible-Infrared Imaging Radiometer Suite (VIIRS) was launched October 28, 2011 on-board the Suomi National Polar-orbiting Partnership (NPP) spacecraft as a primary sensor. It has 22 bands: 14 reflective solar bands (RSBs), 7 thermal emissive bands (TEBs) and a Day Night Band (DNB). The RSBs are calibrated using the sun as a source, after attenuation and reflection of sunlight from a Solar Diffuser (SD). To track SD degradation over time, VIIRS incorporates a separate instrument called the Solar Diffuser Stability Monitor (SDSM). The SDSM is a ratio radiometer using views of attenuated direct solar illumination and solar illumination reflected off the SD to track relative change in the SD reflectance over time. This paper will describe the SDSM design and analysis methodology as well as compare the SD degradation trends with its heritage sensor MODIS.