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Directional infrared temperature and emissivity of vegetation: Measurements and modelsDirectional thermal radiance from vegetation depends on many factors, including the architecture of the plant canopy, thermal irradiance, emissivity of the foliage and soil, view angle, slope, and the kinetic temperature distribution within the vegetation-soil system. A one dimensional model, which includes the influence of topography, indicates that thermal emissivity of vegetation canopies may remain constant with view angle, or emissivity may increase or decrease as view angle from nadir increases. Typically, variations of emissivity with view angle are less than 0.01. As view angle increases away from nadir, directional infrared canopy temperature usually decreases but may remain nearly constant or even increase. Variations in directional temperature with view angle may be 5C or more. Model predictions of directional emissivity are compared with field measurements in corn canopies and over a bare soil using a method that requires two infrared thermometers, one sensitive to the 8 to 14 micrometer wavelength band and a second to the 14 to 22 micrometer band. After correction for CO2 absorption by the atmosphere, a directional canopy emissivity can be obtained as a function of view angle in the 8 to 14 micrometer band to an accuracy of about 0.005. Modeled and measured canopy emissivities for corn varied slightly with view angle (0.990 at nadir and 0.982 at 75 deg view zenith angle) and did not appear to vary significantly with view angle for the bare soil. Canopy emissivity is generally nearer to unity than leaf emissivity may vary by 0.02 with wavelength even though leaf emissivity. High spectral resolution, canopy thermal emissivity may vary by 0.02 with wavelength even though leaf emissivity may vary by 0.07. The one dimensional model provides reasonably accurate predictions of infrared temperature and can be used to study the dependence of infrared temperature on various plant, soil, and environmental factors.
Document ID
19950010659
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Norman, J. M.
(EG and G Energy Measurements, Inc. Las Vegas, NV., United States)
Castello, S.
(EG and G Energy Measurements, Inc. Las Vegas, NV., United States)
Balick, L. K.
(EG and G Energy Measurements, Inc. Las Vegas, NV., United States)
Date Acquired
August 16, 2013
Publication Date
January 1, 1994
Publication Information
Publication: CNES, Proceedings of 6th International Symposium on Physical Measurements and Signatures in Remote Sensing
Subject Category
Earth Resources And Remote Sensing
Accession Number
95N17074
Funding Number(s)
CONTRACT_GRANT: NAGW-1469
CONTRACT_GRANT: NAGW-2536
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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