HR: 0800h
AN: B41B-0186    [Abstracts]
TI: Mechanistic explanations of correlations between MODIS EVI and carbon flux in a wide range of vegetation types across North America.
AU: * Sims, D A
EM: dasims@bsu.edu
AF: Ball State University, Department of Geography, Muncie, IN 47306
AU: Rahman, A F
EM: faiz.rahman@ttu.edu
AF: Texas Tech University, Department of Range Wildlife and Fisheries , Lubbock, TX 79409
AU: Cordova, V D
EM: vdcordova@bsu.edu
AF: Ball State University, Department of Geography, Muncie, IN 47306
AU: El-Masri, B Z
EM: bassil.el-masri@ttu.edu
AF: Texas Tech University, Department of Range Wildlife and Fisheries , Lubbock, TX 79409
AB: Current remote sensing based models of vegetation-atmosphere carbon exchange are complex and require a large number of input parameters not all of which can be determined directly from remote sensing. Models based entirely on remote sensing data would simplify the estimation of vegetation carbon fluxes and potentially reduce errors associated with estimation of ground based parameters. We examined the relationship between the enhanced vegetation index (EVI) from the MODIS satellite sensor and gross carbon flux measurements from 10 eddy covariance towers in a wide range of vegetation types across the United States (US). There was a strong general relationship (r² = 0.60) between EVI and gross flux when all the data were considered together. In fact, this correlation was as good as that between the MODIS GPP product and measured gross flux (r² = 0.54), suggesting that EVI could be used as a simple alternative to more complex models. However, the strength of the relationship between EVI and gross flux varied widely when data for individual sites were considered alone. Although there was a tendency for sites with deciduous vegetation to have better correlations than those with evergreen vegetation, some of the evergreen forest sites also had reasonably strong correlations. Sites in the western US had weaker correlations between EVI and gross flux than those in the eastern US. The strength of the correlation between EVI and gross flux was a function of the amount of summer rainfall and the minimum winter temperature at each site. This may be a result of climatic effects on the amount of understory vegetation (which tends to be deciduous even when the overstory is evergreen) and the phenology of changes in vegetation greenness relative to carbon flux. We explored the mechanistic explanations for these relationships across vegetation types, geographic locations and climatic variability. Better understanding of those factors that lead to good correlations between EVI and gross flux would allow us to use this relationship with confidence for at least a portion of the country and may lead to development of other simple models for carbon flux in areas where the EVI/gross flux relationship is weak.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0480 Remote sensing
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
DE: 3322 Land/atmosphere interactions (1218, 1631, 1843)
SC: Biogeosciences [B]
MN: Fall Meeting 2005