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Optical Engineering

Effect of three-dimensional canopy architecture on thermal infrared exitance
Author(s): James Alan Smith; Jerrell R. Ballard; Jeffrey A. Pedelty
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Paper Abstract

We present a theoretical study of the effects of threedimensional canopy structure on directional thermal infrared exitance. A physics-based model employing steady-state energy budget formulations is used to compute scene element temperatures. Two approaches are then used to combine soil and vegetation contributions to the composite scene response. One method uses a plane-parallel abstraction of canopy architecture to estimate canopy view factors for weighting of soil and vegetation emission terms. The second approach employs computer graphics and rendering techniques to estimate 3-D canopy view factors and scene shadows. Both approaches are applied to a test agricultural scene and compared with available measurements. The models correctly estimate hemispherically averaged thermal infrared exitance to within experimental error with root-mean-square errors of 15.3 W m-2 for the 1-D model and 12.5 W m-2 for the 3-D model. However, the 1-D model systematically underestimates exitance at high sun angles. Explicit modeling of canopy 3-D row structure indicates potential directional anisotropy in brightness temperature of up to 14°C.

Paper Details

Date Published: 1 November 1997
PDF: 8 pages
Opt. Eng. 36(11) doi: 10.1117/1.601527
Published in: Optical Engineering Volume 36, Issue 11
Show Author Affiliations
James Alan Smith, NASA Goddard Space Flight Ctr. (United States)
Jerrell R. Ballard, USAE Waterways Experiment Station (United States)
Jeffrey A. Pedelty, NASA Goddard Space Flight Ctr. (United States)


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