Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: October 15, 2008
Publication Date: December 16, 2008
Citation: Houborg, R.M., Anderson, M.C., Kustas, W.P., Prueger, J.H. 2008. Incorporating maps of leaf chlorophyll in a thermal-based two-source energy balance scheme for mapping coupled fluxes of carbon and water exchange at a range of scales [abstract]. American Geophysical Union. 80(53):B51A-0349. Technical Abstract: A light-use efficiency (LUE) based model of canopy resistance was recently implemented within a thermal-based Two-Source Energy Balance (TSEB) scheme facilitating coupled simulations of land-surface fluxes of water, energy and CO2 exchange from field to regional scales (Anderson et al., 2008). The LUE model component computes canopy-scale carbon assimilation and transpiration fluxes and incorporates LUE modifications from biome specific nominal values (ßn) in response to variations in humidity, CO2 concentration, temperature (soil and air), wind speed, and direct beam vs. diffuse light composition. Here we incorporate leaf chlorophyll content (Cab) as a determinant of spatial and temporal variations in ßn as Cab is related to key LUE modulating factors such as crop phenology, vegetation stress and photosynthetic capacity. A linear relationship between ßn and Cab, established from stand-level measurement of LUE for unstressed environmental conditions and a representative set of Cab values for a range of agricultural and natural vegetation groups, is used to distribute ßn over the modeling domain. The technique is tested for an agricultural area near Bushland, Texas by fusing reflective and thermal based remote sensing inputs from SPOT, Landsat, ASTER and aircraft sensor systems. Maps of LAI and Cab are generated by using at-sensor radiances in green, red and near-infrared wavelengths as input to a REGularized canopy reFLECtance (REGFLEC) modeling tool that couples leaf optics (PROSPECT), canopy reflectance (ACRM), and atmospheric radiative transfer (6SV1) model components. Modeled carbon and water fluxes are compared with eddy covariance measurements made in stands of cotton and with fluxes measured by an aircraft flying transects over irrigated and non-irrigated agricultural land and natural vegetation. The technique is flexible and scalable and is portable to continental scales using GOES and MODIS data products. The results demonstrate utility in combining remotely sensed observations in the reflective solar and thermal domains for estimating carbon and water fluxes within a coupled framework.