Abstract
Abstract. 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, state-of-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 conditions. 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 (Rn), soil heat flux (G0), 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 clear-sky 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 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.
Highlights
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
Most of the relevant data, obtained at the Watershed Allied Telemetry Experimental Research (WATER) (Fig. 1) stations to support the parameterization of land surface heat fluxes and the analysis of ASTER images in this paper, consist of surface radiation budget components, surface radiometric temperature, surface albedo, humidity, wind speed and direction measured by the Atmospheric Boundary Layer (ABL) towers and Automatic Weather Stations (AWSs), turbulent fluxes measured by the eddy correlation technique, soil heat flux, soil temperature profiles, soil moisture profiles, and the vegetation state
As the net radiometer at the Guantan station was located within a forest, the data obtained by this instrument are not comparable to satellite observations and are omitted from the subsequent comparisons
Summary
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. Remote-sensing data provided by satellites make it possible to obtain consistent and frequent observations of the spectral albedo and the emittance of radiation from elements in a patchy landscape and on a global scale (Sellers et al, 1990) Land surface variables, such as surface temperature, surface hemispherical albedo, Normalized Difference Vegetation Index (NDVI) and surface thermal emissivity can be derived directly from satellite observations (e.g., Susskind et al, 1984; Che’din et al, 1985; Tucker, 1986; Wan and Dozier, 1989; Menenti et al, 1989; Becker and Li, 1990, 1995; Watson et al, 1990; Baret and Guyot, 1997; Price, 1992; Kahle and Alley, 1992; Li and Becker, 1993; Qi et al, 1994; Schmugge et al, 1995; Sobrino and Raissouni, 2000; Li et al, 2000, 2003; Jia et al, 2003b; Menenti et al, 2001). Most remote-sensing retrieval methods have been applied in homogeneous moist or semiarid regions, and investigations in the heterogeneous landscape of arid and cold regions (e.g., WATER area) using higherresolution satellite data (on the order of 10 ∼ 100 m) are rare or limited
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