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Physical Models of Layered Polar Firn Brightness Temperatures from 0.5 to 2 GHzWe investigate physical effects influencing 0.5-2 GHz brightness temperatures of layered polar firn to support the Ultra Wide Band Software Defined Radiometer (UWBRAD) experiment to be conducted in Greenland and in Antarctica. We find that because ice particle grain sizes are very small compared to the 0.5-2 GHz wavelengths, volume scattering effects are small. Variations in firn density over cm- to m-length scales, however, cause significant effects. Both incoherent and coherent models are used to examine these effects. Incoherent models include a 'cloud model' that neglects any reflections internal to the ice sheet, and the DMRT-ML and MEMLS radiative transfer codes that are publicly available. The coherent model is based on the layered medium implementation of the fluctuation dissipation theorem for thermal microwave radiation from a medium having a nonuniform temperature. Density profiles are modeled using a stochastic approach, and model predictions are averaged over a large number of realizations to take into account an averaging over the radiometer footprint. Density profiles are described by combining a smooth average density profile with a spatially correlated random process to model density fluctuations. It is shown that coherent model results after ensemble averaging depend on the correlation lengths of the vertical density fluctuations. If the correlation length is moderate or long compared with the wavelength (approximately 0.6x longer or greater for Gaussian correlation function without regard for layer thinning due to compaction), coherent and incoherent model results are similar (within approximately 1 K). However, when the correlation length is short compared to the wavelength, coherent model results are significantly different from the incoherent model by several tens of kelvins. For a 10-cm correlation length, the differences are significant between 0.5 and 1.1 GHz, and less for 1.1-2 GHz. Model results are shown to be able to match the v-pol SMOS data closely and predict the h-pol data for small observation angles.
Document ID
20160013720
Document Type
Reprint (Version printed in journal)
Authors
Tan, Shurun (Washington Univ. Seattle, WA, United States)
Aksoy, Mustafa (Ohio State Univ. Cleveland, OH, United States)
Brogioni, Marco (National Council of Research Italy)
Macelloni, Giovanni (National Council of Research Italy)
Durand, Michael (Ohio State Univ. Cleveland, OH, United States)
Jezek, Kenneth C. (Ohio State Univ. Cleveland, OH, United States)
Wang, Tian-Lin (Washington Univ. Seattle, WA, United States)
Tsang, Leung (Washington Univ. Seattle, WA, United States)
Johnson, Joel T. (Ohio State Univ. Cleveland, OH, United States)
Drinkwater, Mark R. (European Space Agency. European Space Research and Technology Center, ESTEC Noordwijk, Netherlands)
Brucker, Ludovic (Universities Space Research Association Greenbelt, MD, United States)
Date Acquired
November 22, 2016
Publication Date
March 16, 2015
Publication Information
Publication: IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing
Volume: 8
Issue: 7
ISSN: 1939-1404
Subject Category
Earth Resources and Remote Sensing
Computer Programming and Software
Report/Patent Number
GSFC-E-DAA-TN27030
Funding Number(s)
CONTRACT_GRANT: NNG11HP16A
Distribution Limits
Public
Copyright
Other
Keywords
layered polar firn emission
coherent
incoherent
Ultra Wide Band Software Defined Radiometer (UWBRAD)
Ice sheet
Brightness temperature
radiative transfer
L-band radiation