CASI-ATM observed and simulated ecohydrological relevant water and energy fluxes

Monitoring of water and energy fluxes is a requirement for assessment of climate and anthropogenic effects on natural and agricultural ecosystems [i]. These fluxes consist of the physical transfers between soil, vegetation and atmosphere. In order to describe these transfers, on local, regional or global scale, and the changes taking place in the compartments it is necessary to have measurements and models to estimate these fluxes. Distributed hydrological models are appropriate tools and are constantly improving the understanding of this cycling of water through soils, vegetation and atmosphere. Also for the relatively new emerging field of ecohydrology estimation of spatially distributed water and energy levels is essential for predicting occurrence of vegetation species under site specific conditions. Since evapotranspiration is a major component of all combined fluxes it deserves to receive the necessary attention. For the estimation of remotely sensed evapotranspiration, the most popular approach is to use surface temperature and vegetation indices at small scale and low resolution satellite imagery to estimate regional fluxes. New developments in thermal airborne (ATM) combining with CASI imagery allow deriving hydrological relevant observations at a resolution of 1-10 m. In this research we propose to estimate on basis of thermal ATM imagery evapotranspiration and other elements of the water and energy balance on a scale, which allows discriminating local wetness and vegetation heterogeneity in relation to differences in soil and vegetation condition. The evapotranspiration in the study area is simulated with the Surface Energy Balance Algorithm for Land (SEBAL) [ii]. The daily total evapotranspiration is calculated for the complete study area, but special attention is given to a grassland area for which detailed soil moisture measured conditions have been obtained. The estimated evapotranspiration values can be related to other hydrological and vegetation conditions, resulting in an increased understanding of the ecohydrological functioning of the study area.status: publishe