ETWatch for monitoring regional evapotranspiration with remote sensing

The remote sensing can provide surface parameters for Evapotranspiration (ET) estimation at regional scale,where-as the traditional approaches just provide points measurement.This paper introduces an ET monitoring system using remote sensing ETWatch,which is an operational processing chain starting from data pre-processing to application products,utilizing spatial information on climate,soil type,land use,vegetation cover,digital elevation,and remote sensed land surface parameters.The surface energy balance algorithm for land (SEBAL) and the surface energy system (SEBS) are integrated into ET-Watch to estimate surface fluxes on clear-sky condition,while the Penmon-Monteith is applied to retrieved daily ET based on the surface resistence model,the meteorological data and the surface parameters from remote sensing.The application of ET-Watch in Haihe basin is demonstrated for year 2002 to 2005,and a validation is carried by comparing the field fluxes measurement and the hydrological records with the model estimation.The results show that when the energy closure ratio (ECR) of eddy covariance (EC) technique is above 0.9,average deviation of daily ET at the 1 km scale is below 10%; at the 30 m field scale,compared with water consumption from soil-moisture-depletion-method,average deviation of remote sensed daily crop ET is about 12.7%.