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Abstract
Global Land Surface Satellite-downward surface shortwave radiation (GLASS-DSSR) products have been routinely produced from 2008–2010 based on an improved look-up table algorithm, which explicitly accounts for the variations of cloud optical depth, water vapor content, and elevation. In this study, we validated and assessed the accuracy of these products in arid and semiarid regions of China. Toward this goal, observation data-sets provided by the Arid and Semiarid Region Collaborative Observation Project as well as four other metrological sites were collected, chosen, and preprocessed for the final validation. Due to the possible effect of spatial collocation and the strong adjacency pixel effect in instantaneous products, we used a more sophisticated validating scheme in order to reduce the impacts from these effects as much as possible. Evidences indicate that the GLASS-DSSR products are considerably accurate over most parts of arid and semiarid regions in China, but in complex terrain areas the products might need further refinements. The R2 at all sites (except Naqu) was larger than 0.8 with a root mean square error (RMSE) range of about in 90–130 W/m2. Linear regression analyses suggest that GLASS-DSSR products tend to overestimate DSSR in the interval of low surface-measured values and symmetrically underestimate DSSR in the interval of high values. This systematic error may result from inappropriate assumptions about clouds and aerosol loadings over the regions in the operational algorithm.
Acknowledgments
The authors would like to thank the Arid and Semi-arid Region Collaborative Observation Project (ASRCOP) and Watershed Allied Telemetry Experimental Research (WATER) program, which provided in situ measurements for our validation. This work was supported by Key Project of National Natural Science Foundation of China (grant 91125002), National Natural Science Foundation of China (grant 41101389), and Chinese Academy of Sciences Action Plan for West Development Program (grant KZCX2-XB3-15-4).