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Relationship between satellite‐derived spectral brightness and evapotranspiration from a grassland
Author(s) -
Kondoh A.,
Higuchi A.
Publication year - 2001
Publication title -
hydrological processes
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.222
H-Index - 161
eISSN - 1099-1085
pISSN - 0885-6087
DOI - 10.1002/hyp.238
Subject(s) - grassland , evapotranspiration , satellite , brightness , environmental science , remote sensing , geology , physics , ecology , optics , biology , astronomy
This paper presents a correlation between evapotranspiration calculated by the heat budget method using eddy correlation and visible plus near‐infrared information from Landsat Thematic Mapper (TM) images of a grass‐covered site at the Terrestrial Environment Research Center, University of Tsukuba. Eighty Landsat TM images from its 1984 launch until 1998 were collected, and the digital numbers at the site were extracted. The spectral brightness and normalized difference vegetation index (NDVI) are compared with measured evapotranspiration. These data suggest that the vegetation index is a good index of transpiration; however, the relationship differs between the growing season and the mature period. The reflected brightness in the near‐infrared band increased during the spring–summer growing season, whereas red brightness decreased during the same period. Since the red wavelength plays an important role in photosynthetic activity, the data in the red band seems to contain information on the physiological activity of the grass. In the mature season after summer, the red brightness value becomes almost constant and evapotranspiration is best correlated with the near‐infrared brightness, which is related to incident solar radiation. The relationship between NDVI and evapotranspiration should be considered separately for the growing and mature seasons because the inherent physics in the relationship differs according to phenological stages. Understanding the relationship between satellite‐derived vegetation phenology and surface flux is useful for delineating basin‐wide hydrological characteristics, since satellite data covers an extensive area and the time changes in spectral brightness were found to provide information about surface flux. Copyright © 2001 John Wiley & Sons, Ltd.