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SIMULATED RELATIONSHIPS BETWEEN SPECTRAL REFLECTANCE, THERMAL EMISSIONS, AND EVAPOTRANSPIRATION OF A SOYBEAN CANOPY 1
Author(s) -
Hope Allen S.,
Petzold Donald E.,
Goward Samuel N.,
Ragan Robert M.
Publication year - 1986
Publication title -
jawra journal of the american water resources association
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.957
H-Index - 105
eISSN - 1752-1688
pISSN - 1093-474X
DOI - 10.1111/j.1752-1688.1986.tb00772.x
Subject(s) - canopy , evapotranspiration , environmental science , leaf area index , atmospheric sciences , water content , albedo (alchemy) , enhanced vegetation index , vegetation (pathology) , remote sensing , hydrology (agriculture) , normalized difference vegetation index , vegetation index , agronomy , geology , botany , ecology , medicine , art , geotechnical engineering , pathology , biology , art history , performance art
A canopy reflectance model is incorporated into a routine for simulating water and energy flows in the soil‐plant‐atmosphere system. The reflectance model is structured tocalculate canopy albedo throughout each simulation period and to determine spectral reflectances at a specified time during the day. Spectral vegetation indices are then calculated from the reflectances and related to the evapotranspiration and thermal response of the canopy. The canopy reflectance model is also used to establish the photo‐sytheticaily active radiation load at various depths in the canopy. Stomatal resistances are calculated using these radiation values and integrated to give the minimum canopy resistance. Actual canopy resistance is obtained by adjusting minimum canopy resistance for environmental stresses such as leaf water potential and leaf temperature. Using data for a soybean canopy, canopy evapotranspiration and temperatures are simulated for a range of leaf area index values and compared with the corresponding spectral vegetation indices. The resuits indicate that the normalized difference spectral index has an inverse linear relationship with canopy temperature, concurring with results obtained from satellite observations. The possibility of using a spectral vegetation index and thermal observations together to parameterize surface moisture availability for evapotranspiration is considered.