## 2 Study Area and Datasets  
### Study Area and Meteorology Data  
The Heihe Watershed Allied Telemetry Experimental Research (HiWATER) program supports watershed-scale eco-hydrological experiments designed from an interdisciplinary perspective to address complex problems related to impacts of heterogeneity, scaling, and uncertainty in closing the water cycle [32]. One of the three key experimental areas of HiWATER is located in the middle reaches of Heihe, which is an artificial oasis ecosystem containing irrigated agriculture along with wetland and desert components. The first thematic experiment launched in HiWATER was the Multi-Scale Observation Experiment on Evapotranspiration over heterogeneous land surface (HiWATER-MUSOEXE). This experiment involved a flux observation matrix including a network of 21 flux towers deployed over oasis-desert surfaces in the middle reach of the Heihe River Basin from May to September in 2012 [33]. In this study, the upwelling and downwelling longwave radiation measured from the four-component radiometers installed at the flux towers are collected to compute land surface temperature for validating the land surface temperature retrieved from ASTER TIR data. Combining the uncertainty or error in sensor calibration, assumed emmissivity, and the spatial heterogeneity, the uncertainty in site-specific land surface temperature is likely to be on the order of 1.0 K [34]. At these sites, meteorological, soil and vegetation parameters, e.g., fraction of vegetation coverage, soil temperatures and moistures at multiple depths were measured. Soil and vegetation component emissivities were estimated using FT-IR spectrometer (102 F) measurements applied to the Iterative Spectrally Smooth Temperature Emissivity Separation (ISSTES) algorithm. The composite emissivity was computed from the measured soil and vegetation component emissivities based on fractional vegetation cover estimates. In addition, a Fluke Ti55 thermal infrared camera was manually operated on a 25-m-high platform on a flux tower at site 15 (Daman superstation, presented in Figure 1 to measure the thermal radiation of the cropland during the HiWATER experiment. The images including VNIR and TIR were recorded by the camera. Then, the soil and vegetation component temperatures were calculated according to the fraction of vegetation and soil viewed by the camera based on the VNIR data [35]. Due to a lack of other reliable independent observations of soil and vegetation temperatures, the component temperatures measured from the thermal infrared radiometers were converted to composite surface temperature and then compared to the hemispherical observations from the tower-based four-component radiometer [36]. A mean bias of 0.6 K and a root mean square error of 1.67 K was obtained, with the bias indicating a tendency for the thermal-infrared sensors to estimate a higher temperature compared to the hemispherical temperature from the four-component radiometers. Finally, the atmospheric profiles including air pressure, mean air temperature, mean air humidity, visibility and elevation were collected from the meteorological station in Zhangye City on DOY 167, 176, 192, 215, 224, 231, 240, 247 and 256.