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Proceedings Paper

Changes in apparent emissivity as a function of viewing geometry
Author(s): Christopher J. Deloye; Michael S. West; John M. Grossmann
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Paper Abstract

We reiterate the fact that the apparent emissivity of a solid surface can depend on not only the composition and particle size distribution comprising the surface but also on view-angle relative to the bulk surface geometry. We report on experiments measuring the longwave infrared emissivity of quartz sand samples sorted by particle size and observed at a series of view angles up to 60° away from the normal to the bulk sample surface. We show that particle-size and view-angle effects on the apparent emissivity of our quartz samples can mimic each other. In circumstances where significantly off-normal view-angles are unavoidable and characterizing surface qualities are desired, these two effects could be confused. We discuss the existing explanations for these effects. We argue that the view-angle emissivity dependence is intrinsically a bulk geometric effect, not due to a change in apparent particle-size (via coarse grains obscuring finer ones at larger view-angles). We summarize the predominant qualitative explanations of the particle-size effects and review the literature comparing quantitative models and observations. We argue that the existing quantitative models are inadequate for explaining the observations, pointing to a need for further work in this area.

Paper Details

Date Published: 8 June 2011
PDF: 12 pages
Proc. SPIE 8040, Active and Passive Signatures II, 80400J (8 June 2011); doi: 10.1117/12.887737
Show Author Affiliations
Christopher J. Deloye, MITRE Corp. (United States)
Michael S. West, MITRE Corp. (United States)
John M. Grossmann, MITRE Corp. (United States)

Published in SPIE Proceedings Vol. 8040:
Active and Passive Signatures II
G. Charmaine Gilbreath; Chadwick Todd Hawley, Editor(s)

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