14 December 2016 MODIS solar diffuser on-orbit degradation characterization using improved SDSM screen modeling
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Abstract
The Solar Diffuser (SD) is used for the MODIS reflective solar bands (RSB) calibration. An on-board Solar Diffuser Stability Monitor (SDSM) tracks the degradation of its on-orbit bi-directional reflectance factor (BRF). To best match the SDSM detector signals from its Sun view and SD view, a fixed attenuation screen is placed in its Sun view path, where the responses show ripples up to 10%, much larger than design expectation. Algorithms have been developed since the mission beginning to mitigate the impacts of these ripples. In recent years, a look-up-table (LUT) based approach has been implemented to account for these ripples. The LUT modeling of the elevation and azimuth angles is constructed from the detector 9 (D9) of SDSM observations in the MODIS early mission. The response of other detectors is normalized to D9 to reduce the ripples observed in the sun-view data. The accuracy of all detectors degradation estimation depends on how well the D9 approximated. After multiple years of operation (Terra: 16 years; Aqua: 14 years), degradation behavior of all detectors can be monitored by their own. This paper revisits the LUT modeling and proposes a dynamic scheme to build a LUT independently for each detector. Further refinement in the Sun view screen characterization will be highlighted to ensure the degradation estimation accuracy. Results of both Terra and Aqua SD on-orbit degradation are derived from the improved modeling and curve fitting strategy.
Conference Presentation
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H. Chen, H. Chen, X. Xiong, X. Xiong, A. Angal, A. Angal, Z. Wang, Z. Wang, A. Wu, A. Wu, } "MODIS solar diffuser on-orbit degradation characterization using improved SDSM screen modeling", Proc. SPIE 10000, Sensors, Systems, and Next-Generation Satellites XX, 100000X (14 December 2016); doi: 10.1117/12.2239950; https://doi.org/10.1117/12.2239950
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