Temporal upscaling of remote sensing instantaneous evapotranspiration estimated at two satellite overpass times

Abstract

Quantification of land surface evapotranspiration (ET) at daily or longer time scales is of great significance in agricultural ecosystem and hydrologic cycle. Temporal upscaling of instantaneous remote sensing-based ET to daily or longer time scales is generally only based on a single instantaneous estimate. A test is made to use two instantaneous ET estimates for the daily upscaling. The results show that the temporal upscaling using two instantaneous ET estimates is superior to that using only single instantaneous ET estimate for the constant extraterrestrial solar radiation ratio (R p ) method, the constant global solar radiation ratio (R g ) method, and the constant evaporative fraction (EF) method. The largest improvement of daily ET estimation occurs when instantaneous ET in the morning is combined with that in the afternoon for the R p and R g methods, while the for EF method the optimal combination comprises of two moments in the afternoon.