On the relationship between nominal light use efficiency and leaf chlorophyll

A light-use-efficiency (LUE)-based model of canopy resistance has been embedded into a thermal-based Two-Source Energy Balance (TSEB) model to facilitate coupled simulations of transpiration and carbon assimilation. The model assumes that deviations of the observed canopy LUE from a nominal stand-level value (LUEn - typically indexed by vegetation class) are due to varying conditions of light, humidity, CO₂ concentration and leaf temperature. The deviations are accommodated by adjusting an effective LUE that responds to the varying conditions. We investigate the feasibility of leaf chlorophyll (Cab) to capture these variations in LUEn using remotely sensed data. To retrieve Cab from remotely sensed data we use REGFLEC, a physically based tool that translates at-sensor radiances in the green, red and NIR spectral regions from multiple satellite sensors into realistic maps of LAI and Cab. Initial results show that using Cab to estimate LUE allows for improved flux estimates over a soybean field in Iowa. The improved results indicate the necessity of a varying LUE during times of stresses induced by the environment. The results also indicate that using remotely sensed Cab to estimate LUE will allow for more accurate estimates of fluxes over space and time.