17 May 2016 Impact of MODIS SWIR band calibration improvements on Level-3 atmospheric products
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Abstract
The spectral reflectance measured by the MODIS reflective solar bands (RSB) is used for retrieving many atmospheric science products. The accuracy of these products depends on the accuracy of the calibration of the RSB. To this end, the RSB of the MODIS instruments are primarily calibrated on-orbit using regular solar diffuser (SD) observations. For λ <0.94 μm the SD’s on-orbit bi-directional reflectance factor (BRF) change is tracked using solar diffuser stability monitor (SDSM) observations. For λ <0.94 μm, the MODIS Characterization Support Team (MCST) developed, in MODIS Collection 6 (C6), a time-dependent correction using observations from pseudo-invariant earth-scene targets. This correction has been implemented in C6 for the Terra MODIS 1.24 μm band over the entire mission, and for the 1.38 μm band in the forward processing. As the instruments continue to operate beyond their design lifetime of six years, a similar correction is planned for other short-wave infrared (SWIR) bands as well. MODIS SWIR bands are used in deriving atmosphere products, including aerosol optical thickness, atmospheric total column water vapor, cloud fraction and cloud optical depth. The SD degradation correction in Terra bands 5 and 26 impact the spectral radiance and therefore the retrieval of these atmosphere products. Here, we describe the corrections to Bands 5 (1.24 μm) and 26 (1.38 μm), and produce three sets (B5, B26 correction = on/on, on/off, and off/off) of Terra-MODIS Level 1B (calibrated radiance product) data. By comparing products derived from these corrected and uncorrected Terra MODIS Level 1B (L1B) calibrations, dozens of L3 atmosphere products are surveyed for changes caused by the corrections, and representative results are presented. Aerosol and water vapor products show only small local changes, while some cloud products can change locally by >10%, which is a large change.
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Andrew Wald, Andrew Wald, Robert C. Levy, Robert C. Levy, Amit Angal, Amit Angal, Xu Geng, Xu Geng, Jack Xiong, Jack Xiong, Kurt Hoffman, Kurt Hoffman, } "Impact of MODIS SWIR band calibration improvements on Level-3 atmospheric products", Proc. SPIE 9827, Ocean Sensing and Monitoring VIII, 98270Y (17 May 2016); doi: 10.1117/12.2222594; https://doi.org/10.1117/12.2222594
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