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Proceedings Paper

The characterization of deep convective cloud albedo as a calibration target using MODIS reflectances
Author(s): David R. Doelling; Gang Hong; Dan Morstad; Rajendra Bhatt; Arun Gopalan; Xiaoxiong Xiong
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Paper Abstract

There are over 25 years of historical satellite data available for climate analysis. The historical satellite data needs to be properly calibrated, especially in the visible, for sensors with no onboard calibration. Accurate vicarious calibration of historical satellites relies on invariant targets, such as the moon, Dome C, and deserts. Deep convective clouds (DCC) also show promise of being a stable or predictable target viewable by all satellites, since they behave as solar diffusers. However DCC have not been well characterized for calibration. Ten years of well-calibrated MODIS radiances are now available. DCC can easily be identified using IR thresholds, where the IR calibration can be traced to the onboard blackbodies. The natural variability of the DCC radiance will be analyzed geographically, seasonally, and for differences of convection initiated over land and ocean. Functionality between particle size and ozone absorption with DCC albedo will be examined theoretically. Although DCC clouds are nearly Lambertian, the angular distribution of reflectances will be sampled and compared with theoretical models. Both Aqua and Terra MODIS DCC angular models were compared for consistency. The DCC method was able to identify two calibration coefficient discontinuities in the Terra-MODIS Collection 5 10-year record and validated the calibration stability of MODIS to within 0.1% per decade. The DCC method needs to take into account the functionality of the 0.65μm DCC radiance with the 11μm brightness temperature threshold and the DCC 0.65μm radiance difference observed over the tropical western pacific and the afternoon generated DCC over land. Both of these cases cause a bias on the order of 5%. These improvements are the first steps towards successful use of DCC as an absolute calibration target.

Paper Details

Date Published: 4 November 2010
PDF: 10 pages
Proc. SPIE 7862, Earth Observing Missions and Sensors: Development, Implementation, and Characterization, 78620I (4 November 2010); doi: 10.1117/12.869577
Show Author Affiliations
David R. Doelling, NASA Langley Research Ctr. (United States)
Gang Hong, Science Systems and Applications, Inc. (United States)
Dan Morstad, Science Systems and Applications, Inc. (United States)
Rajendra Bhatt, Science Systems and Applications, Inc. (United States)
Arun Gopalan, Science Systems and Applications, Inc. (United States)
Xiaoxiong Xiong, NASA Goddard Space Flight Ctr. (United States)

Published in SPIE Proceedings Vol. 7862:
Earth Observing Missions and Sensors: Development, Implementation, and Characterization
Xiaoxiong Xiong; Choen Kim; Haruhisa Shimoda, Editor(s)

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