MODIS solar diffuser stability monitor sun view modeling

The Moderate Resolution Imaging Spectroradiometer (MODIS) reflective solar bands (RSBs) are calibrated on-orbit using an onboard solar diffuser (SD) panel, made of Spectralon. An onboard Solar Diffuser Stability Monitor (SDSM) tracks the SDs degradation. The SDSM views the sun through a 1.44% attenuation screen during SD calibration. The observed SDSM sun view response has shown serious unexpected ripples that are as large as 10% of the averaged response and consequently disable the originally designed SD degradation tracking algorithms. In this report, a model based on geometric factors and design parameters is developed to simulate the SDSM sun view response. It is shown that the ripples are induced by erroneous design parameters and incorrect installation of the involved optical elements. The model could be used to improve the MODIS SD calibration and to provide helpful information for the design of future remote sensing systems.