Determination of continental surface emissivity and temperature from satellite observations.

http://ara.lmd.polytechnique.fr/htdocs-public/products/emissivity/emissivity.html
Surface emission depends on surface parameters, i.e. emissivity and temperature. Emissivity of land surfaces substantially varies with vegetation, soil moisture, composition, and roughness (Nerry et al. (1988); Salisbury and D'Aria (1992)). As emissivity depends on wavelength, it is referred to as spectral emissivity. Emissivity also depends on the viewing angle.

Continental surface emissivity in the thermal infrared window is a key parameter for estimating the surface radiation budget. The energy emitted from the surface is proportional to the spectrally integrated surface emissivity and depends on the surface temperature. A 10% error (from 0.9 to 1.0, for example) on the emissivity approximately corresponds to a 10% error in the energy emitted from the surface (a portion of which may be compensated by the reflected incoming radiation). Prabhakara and Dalu (1976); Ogawa et al. (2003).

Wikipedia on Emissivity

Wikipedia has an entry for emissivity that is very brief and limited as of November 2008. Perhaps some visitors will improve it.

Will check periodically and let you know.

Link: http://en.wikipedia.org/wiki/Emissivity

Prediction of the thermal radiative properties of an X-Ray µ-tomographied porous silica glass

Prediction of the thermal radiative properties of an X-Ray µ-tomographied porous silica glass
B.Rousseau, D.De Sousa Meneses, P.Echegut, M.Di Michiel, J.-F.Thovert
Prediction of the thermal radiative properties of an X-Ray µ-tomographied porous silica glass
Applied Optics 46 4266-4276, (2007)

ABSTRACT
"A Monte Carlo ray tracing procedure is proposed to simulate thermal optical processes in heterogeneous materials. It operates within a detailed 3D image of the material, and it can therefore be used to investigate the relationship between the microstructure, the constituent optical properties, and the macroscopic radiative behavior. The program is applied to porous silica glass. A sample was first characterized by 3D x-ray tomography; then, its normal spectral emittance was calculated and compared with the experimental spectrum measured independently by high-temperature infrared emittance spectroscopy. We conclude with a discussion of the light-scattering mechanisms occurring in the sample."

Work performed at and reported by: Centre National de la Recherche Scientifique (CNRS), France.

Texture and porosity effects on the thermal radiative behavior of alumina ceramics

Texture and porosity effects on the thermal radiative behavior of alumina ceramics
Int. J. Thermophys. (in press) [view]

New Article
By: O.Rozenbaum, D.De Sousa Meneses; P.Echegut
Texture and porosity effects on the thermal radiative behavior of alumina ceramics
Int. J. Thermophys. (in press) [view]
ABSTRACT
"Thermal and optical properties of ceramics are dependent on radiation scattering and cannot be determined by the only knowledge of their chemical composition as for single crystals. In this paper, we investigate extrinsic effects such as roughness, porosity and texture on spectral emissivity of alumina ceramics. Roughness effects have an influence mainly in the opaque zone; an important porosity dependence and the presence of a critical porosity threshold were also pointed out in the semi-transparent zone. Furthermore, it was shown that two ceramics with similar total porosity but with different textures possess radically different emissivities, showing that grain size, pore size and spatial repartition of the grains is also crucial for the comprehension of the ceramics thermal properties"

Work performed at and reported by: Centre National de la Recherche Scientifique (CNRS), France.

Emissivity of Triangular Surfaces Determined by Differential Method

From Homogenization to Validity Limit of Geometrical Optics
Author: Taoufik Ghabara, Faouzi Ghmari and M. Salah Sifaoui
Abstract:

Geometric optics approximation for emissivity from triangular surfaces was compared with exact scattering predictions from electromagnetic theory. Rigorous electromagnetic scattering theory was numerically formulated based on the differential method. We have used a numerical simulation of the emissivity of gold and tungsten for a wavelength equal 0.55 micron to explore the validity of the geometric optics.

Surface parameter domains for the regions of accuracy of the geometric optics approximation are quantified and presented as functions of surface slope and roughness. Influence on the validity of the approximate method of multiple scattering, the shadowing effect and the cavity effect of metallic surface have been investigated.

For the latter, our interest was focused on the mechanism that enhances the emissivity of an interface when ruling a grating. It has been seen that the mechanism responsible for the enhancement of the emissivity depends very much on the period of the grating.

For gratings with a period much smaller than the wavelength, the roughness essentially behaves as a transition layer with a gradient of the optical index. For different period / wavelength ratio, we have found a good agreement between the differential method and the homogenization regime when the period was smaller.

Journal: American Journal of Applied Sciences
Issn: 15469239
EIssn: 15543641
Year: 2007
Volume: 4
Issue: 3
pages/rec.No: 146-154

DOAJ - Directory of Open Access Journals, 2008, Lund University Libraries, Head Office