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A Fast Hybrid (3-D/1-D) Model for Thermal Radiative Transfer in Cirrus via Successive Orders of ScatteringWe investigate the impact of cirrus cloud heterogeneity on the direct emission by cloud or surface and on the scattering by ice particles in the thermal infrared (TIR). Realistic 3-D cirri are modeled with the 3DCLOUD code, and top-of-atmosphere radiances are simulated by the 3-D Monte Carlo radiative transfer (RT) algorithm 3DMCPOL for two (8.65 micrometers and 12.05 micrometers) channels of the Imaging Infrared Radiometer on CALIPSO. At nadir, comparisons of 1-D and 3-D RT show that 3-D radiances are larger than their 1-D counterparts for direct emission but smaller for scattered radiation. For our cirrus cases, 99% of the 3-D total radiance is computed by the third scattering order, which corresponds to 90% of the total computational effort, but larger optical thicknesses need more scattering orders. To radically accelerate the 3-D RT computations (using only few percent of 3-D RT time with a Monte Carlo code), even in the presence of large optical depths, we develop a hybrid model based on exact 3-D direct emission, the first scattering order from 1-D in each homogenized column, and an empirical adjustment linearly dependent on the optical thickness to account for higher scattering orders. Good agreement is found between the hybrid model and the exact 3-D radiances for two very different cirrus models without changing the empirical parameters. We anticipate that a future deterministic implementation of the hybrid model will be fast enough to process multiangle thermal imagery in a practical tomographic reconstruction of 3-D cirrus fields.
Document ID
20170002251
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Fauchez, Thomas
(Universities Space Research Association Greenbelt, MD, United States)
Davis, Anthony B.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Cornet, Celine
(Lille Univ. France)
Szczap, Frederic
(Universite Blaise Pascal Clermont-Ferrand, France)
Platnick, Steven
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Dubuisson, Philippe
(Lille Univ. France)
Thieuleux, Francois
(Lille Univ. France)
Date Acquired
March 14, 2017
Publication Date
January 6, 2017
Publication Information
Publication: Journal of Geophysical Research
Publisher: Wiley
Volume: 122
Issue: 1
ISSN: 2169-897X
Subject Category
Meteorology And Climatology
Report/Patent Number
GSFC-E-DAA-TN39461
Funding Number(s)
CONTRACT_GRANT: NNH15CO48B
Distribution Limits
Public
Copyright
Other
Keywords
radiative transfer
global modeling
clouds

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