Land surface heat fluxes are essential measures of the strengths of land-atmosphere interactions involving energy, heat and water. Correct parameterization of these fluxes in climate models is critical. Despite their importance, stateof-the-art observation techniques cannot provide representative areal averages of these fluxes comparable to the model grid. Alternative methods of estimation are thus required. These alternative approaches use (satellite) observables of the land surface

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... In this study, the Surface Energy Balance System (SEBS) algorithm was evaluated in a cold and arid environment, using land surface parameters derived from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data. Field observations and estimates from SEBS were compared in terms of net radiation flux (R n ), soil heat flux (G 0 ), sensible heat flux (H ) and latent heat flux (λE) over a heterogeneous land surface. As a case study, this methodology was applied to the experimental area of the Watershed Allied Telemetry Experimental Research (WATER) project, located on the mid-to-upstream sections of the Heihe River in northwest China. ASTER data acquired between 3 May and 4 June 2008, under clearsky conditions were used to determine the surface fluxes. Ground-based measurements of land surface heat fluxes were compared with values derived from the ASTER data. The results show that the derived surface variables and the land surface heat fluxes furnished by SEBS in different months over the study area are in good agreement with the observed Correspondence to: W. Ma (wqma@lzb.ac.cn) land surface status under the limited cases (some cases looks poor results). So SEBS can be used to estimate turbulent heat fluxes with acceptable accuracy in areas where there is partial vegetation cover in exceptive conditions. It is very important to perform calculations using ground-based observational data for parameterization in SEBS in the future. Nevertheless, the remote-sensing results can provide improved explanations of land surface fluxes over varying land coverage at greater spatial scales. Introduction A number of land surface process experiments are currently being performed around the world (e.g., Su et al., 2010), but arid and cold regions have received relatively little attention. To understand hydrological and ecological processes at different scales, the land surface fluxes (and estimates thereof) need to be quantified correctly by using a combination of remote sensing and in situ observations in cold and arid regions. WATER was a simultaneous airborne, satellite-borne, and ground-based remote-sensing experiment conducted in the Heihe Basin, the second largest inland river basin in the northwest arid regions of China. The objective of the WA-TER experiment was to investigate the water cycle, ecological hydrology and other land surface processes at the catchment scale. At this scale in the study, surface meteorological observation plays a very important role. These observations provide strong information for validation of the remotesensing results .