A direct algorithm for estimating daily regional Evapotranspiration from modis TOA radiances

Satellite remote sensing is a promising technique for estimating global or regional ET (Evapotranspiration). A simplified single-source energy balance parameterization scheme, known as the surface temperature-vegetation index (T_s-VI) triangle method, has been applied successfully to estimate regional clear sky ET in many studies. On the basis of this approach, we proposed a new method to estimate daily ET directly using the TOA (top of atmosphere) radiances without performing atmospheric correction and other processes. The estimated EF, net radiation and ET have been validated against field observations collected for the period October 2007-July 2008. The results suggest that the proposed method appears to provide daily EF, net radiation and ET with comparable accuracy to those of current widely used satellite-based methods. Overall, the proposed algorithm has fewer assumptions and can avoid the uncertainties associated with the satellite derived products.