Estimation of evapotranspiration based on METRIC and TTME models from Landsat data over heterogeneous land surfaces in arid region of China

Estimating surface evapotranspiration (ET) is extremely important for managing water resources in arid region. Though a number of surface energy balance (SEB) models have been proposed for estimating ET from remote sensed data, there is still no clear guidance on which models are suitable for a specific arid region. In this study, a one-source SEB model named Mapping evapotranspiration at high Resolution with Internalized Calibration (MTRIC), and a two-source SEB model named Two-source Trapezoid Model for Evapotranspiration (TTME), were selected to estimate latent heat flux (LE) in a selected sub-region of the middle reaches of the Heihe River Basin, northwest China. Both METRIC and TTME algorithms, which were developed in MATLAB environment, were applied to retrieve LE from Landsat-8 and Landsat-7 data during the crop growth stage from April to September, 2013. The derived LE with METRIC and TTME were evaluated by observed LE from ECS. The experimental results indicate: 1) The spatial distributions of LE from METRIC and TTME models are similar, with the relative deviation values within 7%. It supposes that the two models are suitable for retrieving LE in this study area. 2) LE retrieval precisions of both METRIC and TTME models are affected by land use/cover types. In desert area, though both METRIC and TTME are suitable for retrieving LE, while METRIC obtained slightly higher accurate values than TTME; in farmland/wetland area, TTME achieved obviously higher LE precision than METRIC.