The improvement of et calculation in winter by introducing radar-based aerodynamic roughness information into ETWatch system

The aerodynamic roughness is one of the major parameters in the evapotranspiration (ET) calculation, which affects the turbulent exchange process between terrestrial and atmosphere. The ETWatch system is developed by integrating SEBS, SEBAL and the improvements to the retrieval of important parameters discussed in the introduction section. At present, the aerodynamic roughness calculation has mainly considered two factors, including NDVI and topography. However, when mapping ET in a large scale with multi-temporal, unavoidably, the situation of flat geographic region in winter season will be met, in which the two above factors both lose effects. In this paper, the satellite-based radar data of ENVISAT ASAR backscattering information in winter was introduced into ETWATCH system to calculate the ET in Guantao County in winter season. The field EC (Eddy Covariance System) and LAS (Large Aperture Scintillometers) measurements data were used to validate the ET results before and after introducing radar-based aerodynamic roughness. The results indicate that the radar-based aerodynamic roughness information is essential for ET calculation in winter season in the flat region. It can decrease the original ET to a proper extent, which is more agreeable to field measurements.