Measurements of Hydrological Variables from Satellite: Application to Mediterranean Regions

Abstract

The present research is devoted to investigate the surface energy balance and estimate the surface energy fluxes and the evaporative fraction over extended areas. The fluxes of heat and moisture at the land surface determine the regional water balance, and they affect the development and evolution of weather and climate Systems as well as hydrological events. Research and model simulations are showing how forecast of extreme events significantly improves using distributed information of soil moisture or heat surface fluxes. Furthermore recent applications prove how the use of soil moisture indexes can facilitate the calibration of distributed hydrological models on ungauged basins. Following these rising needs of land surface measurements, for different application field, satellite data assimilation could be used to supply the estimation of those variables. Data assimilation techniques provide a useful framework which allow to combine measurements and model to produce an optimal and dynamically consistent estimate of the evolving state of the system. A variational assimilation scheme is here used as basis to estimate variables related to atmosphere-surface interaction processes. Land Surface Temperature, estimated both from polar and geostationary satellite platform, is the assimilated variable. Introducing precipitation information allows a more robust estimation scheme and a better simulation of soil moisture condition and surface fluxes partitioning. The model is implemented over mediterranean regions assimilating SEVIRI, AVHRR and MODIS data.