Estimating Evapotranspiration Using Triangle Method with Topographic Correction from MODIS Data in Taihu Basin, China

Abstract

Many water resources and agricultural applications require the knowledge of evapotranspiration (ET) over a range of spatial and temporal scales. Satellite remote sensing provides an unprecedented spatial coverage of land surface and atmospheric data that are logistically and economically impossible to obtain through ground based observation networks. The surface temperature-normalized difference vegetation index (Ts-NDVI) triangle method based on remote sensing datasets was widely applied to estimate regional ET. However, little research focused on influence of topography on triangle method application in complex topographic areas. To retrieve more accurate ET, topographic correction should be employed in mountainous areas. In this study, we estimate ET by triangle method with topographic correction from MODIS datasets in Taihu Basin, China. The evaporative fraction (EF), defined as the ratio of ET and available radiant energy, was estimated by the triangle method with topographic correction. And then, spatially distributed net radiation (Rn) maps were retrieved as an estimate of available energy to get both the spatial and temporal distribution maps of ET for clear sky days. Our results indicate that topographic correction improve to determine quantitatively the dry and wet edges of Ts-NDVI triangle space in Taihu Basin, and the EF value in mountainous area become more reasonable than before correction. The Rn retrieved is in good agreement with ground-based measurements with a correlation of 0.80 on average. The ET estimated, was validated by evaporation pan measurements in Taihu Lake station, showed consistent pattern compare to measurements.