From Event: SPIE Optical Engineering + Applications, 2018
This study presents a modeling approach to improve solar diffuser (SD) degradation determination from SD stability monitor (SDSM) measurements. The MODIS instrument uses a SD to calibrate its reflective solar bands (RSBs) on-orbit. Due to the imperfectly designed SDSM sun view screen, the SD reflectance tracked by SDSM has large noise. The SDSM measurements noise is spectrally coherent and can be minimized by normalizing measurements to the least degraded detector 9 (936 nm). In this study, a SD degradation model is used to determine the SD degradation’s wavelength dependency and the detector 9 degradation is estimated by the model solution. The results show the SD degradations measured at 6 SDSM detectors (554 - 936 nm) have stable relationships, where the degradation is inversely proportion to 1/wavelength^4. The model estimated SD degradation at SDSM detector 9 wavelength (936 nm) is ~0.9% from 2002 to 2018. Based on the SD degradation model solution, the SD degradation at short/mid wave bands are estimated to improve short/mid wave bands calibration. The model can also be used to improve interpolating SD degradation at SDSM detectors to RSB wavelengths. Compared to linear interpolation, bands 9 and 10 show the largest differences of up to 0.3 and 0.4% respectively. These differences directly impact the calibration coefficients of these bands.
Shihyan Lee and Gerhard Meister, "MODIS solar diffuser degradation determination and its spectral dependency," Proc. SPIE 10764, Earth Observing Systems XXIII, 1076414 (Presented at SPIE Optical Engineering + Applications: August 23, 2018; Published: 7 September 2018); https://doi.org/10.1117/12.2321392.
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