**Implementation of EF from SEBS in a LUE Model in a Rapeseed Cropland**
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Pardo, N. ^{1}; Timmermans, J.^{2}; Pérez, I. A.^{1}; García, M. A.^{1}; Su, Z.^{2}; Sánchez, M. L.^{1}
^{1}Dept. of Applied Physics, University of Valladolid (UVA), SPAIN; ^{2}Dept. of Water Resources, ITC, University of Twente, NETHERLANDS
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In assessment of global carbon cycle, evaluation of gross primary production (GPP) of an ecosystem is the main endeavour. The most adequate way to address this study is to apply a Light Use Efficiency (LUE) model in combination with an Eddy Covariance (EC) system.

LUE model is based on the linear relationship between GPP and FaPAR, where FaPAR is the product of on ground PAR measurements and FPAR provided by MERIS/MODIS. In this model, water and temperature stress is taking into account using a scalar factor varying between 0 and 1.

Temperature stress is dependent on air temperature and water stress is assumed to be equal to the evaporative fraction. Evaporative fraction (EF) is calculated using two separately procedures. First, in-situ measurements of latent and sensible heat were used. Then, EF results from SEBS (Surface Energy Balance System) algorithm developed by ITC were employed.

In this paper, EF from two different databases is applied to a LUE model in order to calculate a final ε_{max} value which is the maximum efficiency of radiation conversion of the cropland.

The LUE model was found to fit properly using both EF databases, with squared correlation coefficients of 0.889 and 0.814 for field measurements and SEBS results, respectively. Final values for maximum efficiency were of 2.821±0.185 gC MJ^{-1} (measured EF) and 2.588±0.226 gC MJ^{-1} (SEBS). All these results were obtained with FPAR provided by MERIS; however, FPAR values from MODIS were employed in the LUE model too, obtaining similar final results with minor differences to those presented in this paper.