Abstract
In this article, we comprehensively assessed the newly released long-term high-spatial-resolution Global LAnd Surface Satellite (GLASS) surface longwave (LW) radiation product using site measurements of LW fluxes. In total, three years of ground-measured LW fluxes (surface longwave upward radiation (LWUP), surface longwave downward radiation (LWDN), and surface longwave net radiation (LWNR) collected from 141 sites in six independent networks (AmeriFlux, AsiaFlux, BSRN, CEOP, HiWATER-MUSOEXE, and TIPEX-III) are used to evaluate the GLASS LW radiation product. These sites cover various land cover types, surface elevations, and climatic types. According to the evaluation results, the biases are -4.33, -3.77, and 0.70 W/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and the RMSEs are 18.15, 26.94, and 26.70 W/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for clear-sky LWUP, LWDN, and LWNR, respectively. The GLASS LW radiation product performs well in climate-change-sensitive areas such as poleward areas, semiarid areas, and the “third pole”, namely, the Tibetan Plateau. The accuracy of the GLASS LW product is higher or comparable to that of available LW products and studies but has a high-spatial-resolution of 1 km and a time span of 19 years. In conclusion, the overall accuracy of the clear-sky GLASS LW radiation product can satisfy the requirements of the hydrological, meteorological, and agricultural research communities on a global scale. We will continue to improve the retrieval algorithms and update the products accordingly.
Highlights
T HE surface longwave (LW) radiation (4–100 μm) is one of the two components of the surface radiation budget (SRB), and it consists of the surface longwave upward radiation (LWUP), the surface longwave downward radiation (LWDN), and the surface longwave net radiation (LWNR) [1], [2]
Two indices are used to characterize the accuracy of the Global LAnd Surface Satellite (GLASS) LW radiation product, namely, the bias and the root-mean-square error (RMSE), which are defined as follows: 1N
In view of the significant role of satellite-derived surface LW radiation products in the study of climate change and the need by related research communities for long-time-series high-quality surface LW radiation products, we developed algorithms for the retrieval of high-spatial-resolution surface LW radiation products and we produced a long-time-series all-sky instantaneous GLASS LW radiation product
Summary
T HE surface longwave (LW) radiation (4–100 μm) is one of the two components of the surface radiation budget (SRB), and it consists of the surface longwave upward radiation (LWUP), the surface longwave downward radiation (LWDN), and the surface longwave net radiation (LWNR) [1], [2]. LW radiation can be measured directly at ground sites. Ground-based measurements are expensive, and the sites are limited in number and sparsely distributed around the globe [10]. Satellite remote sensing is the only available technology for acquiring high-spatial-resolution LW radiation products. Substantial efforts have been made to use remote sensing to estimate of surface LW product, and many algorithms have been proposed
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