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Optimum combinations of visible and near-infrared reflectances for estimating the fraction of photosynthetically available radiation absorbed by plantsA useful parameter to estimate terrestrial primary productivity, that can be sensed from space, is the daily averaged fraction of Photosynthetically Available Radiation (PAR) absorbed by plants. To evaluate this parameter, investigators have relied on the fact that the relative amount of radiation reflected by a vegetated surface in the visible and near infrared depends on the fraction of the surface covered by the vegetation and therefore, correlates with absorbed PAR. They have used vegetation indices, namely normalized difference and simple ratio, to derive absorbed PAR. The problem with normalized difference and simple ratio is first, they are non linear functions of radiance or reflectance and therefore, cannot be readily applied to heterogeneous targets, second, they are used in generally nonlinear relationships, which make time integrals of the indices not proportional to primary productivity, and third, the relationships depend strongly on the type of canopy and background. To remove these limitations, linear combinations of visible and near infrared reflectances at optimum (one or two) viewing zenith angles are proposed.
Document ID
19920002256
Document Type
Conference Paper
Authors
Podaire, Alain (Centre National d'Etudes Spatiales Toulouse (France)., United States)
Deschamps, Pierre-Yves (Scripps Institution of Oceanography La Jolla, CA., United States)
Frouin, R. (Scripps Institution of Oceanography La Jolla, CA., United States)
Asrar, Ghassem (NASA Headquarters Washington, DC United States)
Date Acquired
September 6, 2013
Publication Date
May 1, 1991
Publication Information
Publication: ESA, Physical Measurements and Signatures in Remote Sensing, Volume 1
Subject Category
EARTH RESOURCES AND REMOTE SENSING
Funding Number(s)
CONTRACT_GRANT: NAGW-1968
CONTRACT_GRANT: NAG5-900
CONTRACT_GRANT: CS-76-90
Distribution Limits
Public
Copyright
Other