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20 August 2008 Assessment of MODIS scan mirror reflectance changes on-orbit
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Abstract
Since their respective launches in December 1999 and May 2002, NASA's EOS Terra and Aqua MODIS have successfully operated on-orbit for more than 8.5 and 6 years. MODIS collects data using a two-sided scan mirror over a large scan angle range. It has 36 spectral bands with wavelengths ranging from visible (VIS) to long-wave infrared (LWIR). The scan mirror is made of a polished, nickel-plated beryllium base coated with high purity silver, which is then over-coated with the Denton proprietary silicon monoxide and silicon dioxide mixture. The scan mirror's reflectance was characterized pre-launch using its witness samples, and the response versus scan angle (RVS) was measured at the sensor system level. In this study, we present an assessment of the MODIS scan mirror's on-orbit degradation by examining changes in spectral band responses over each sensor's mission lifetime. On-orbit results show that the scan mirror's optical properties for both Terra and Aqua MODIS have experienced significant degradation in the VIS spectral region. The degradation is mirror side dependent as well as scan angle dependent. For MODIS spectral bands at longer wavelengths, the degradation is relatively small. For Terra MODIS, the VIS spectral band degradation is noticeably different between the mirror sides, with bands 8 and 9 showing the largest differences, up to 10%. In contrast, the mirror side differences in Aqua MODIS are much smaller for all spectral bands. Also illustrated in this paper are examples of the mirror side differences, before and after on-orbit correction.
© (2008) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
X. Xiong, A. Wu, and A. Angal "Assessment of MODIS scan mirror reflectance changes on-orbit", Proc. SPIE 7081, Earth Observing Systems XIII, 70810B (20 August 2008); https://doi.org/10.1117/12.792705
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