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Modeling thermal infrared (2-14 micrometer) reflectance spectra of frost and snowExisting theories of radiative transfer in close-packed media assume that each particle scatters independently of its neighbors. For opaque particles, such as are common in the thermal infrared, this assumption is not valid, and these radiative transfer theories will not be accurate. A new method is proposed, called 'diffraction subtraction', which modifies the scattering cross section of close-packed large, opaque spheres to account for the effect of close packing on the diffraction cross section of a scattering particle. This method predicts the thermal infrared reflectance of coarse (greater than 50 micrometers radius), disaggregated granular snow. However, such coarse snow is typically old and metamorphosed, with adjacent grains welded together. The reflectance of such a welded block can be described as partly Fresnel in nature and cannot be predicted using Mie inputs to radiative transfer theory. Owing to the high absorption coefficient of ice in the thermal infrared, a rough surface reflectance model can be used to calculate reflectance from such a block. For very small (less than 50 micrometers), disaggregated particles, it is incorrect in principle to treat diffraction independently of reflection and refraction, and the theory fails. However, for particles larger than 50 micrometers, independent scattering is a valid assumption, and standard radiative transfer theory works.
Document ID
19950048359
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Wald, Andrew E.
(Johns Hopkins University Baltimore, MD, United States)
Date Acquired
August 16, 2013
Publication Date
December 10, 1994
Publication Information
Publication: Journal of Geophysical Research
Volume: 99
Issue: B12
ISSN: 0148-0227
Subject Category
Earth Resources And Remote Sensing
Accession Number
95A79958
Funding Number(s)
CONTRACT_GRANT: NAS5-31373
Distribution Limits
Public
Copyright
Other

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