摘要：The derivation of widely used geometric optical (GO) kernels in bidirectional reflectance distribution function models, that is, LiSparseReciprocal kernel ( K GOLSR ) and LiDenseReciprocal kernel, was based on two important assumptions: (1) The shaded components are perfect black and (2) the contributions of two sunlit components are identical. Different from the bidirectional reflectance, thermal radiation directionality effect mainly results from component temperature differences, suggesting the above assumptions are not applicable in most situations. Therefore, this study derived GO kernels for thermal radiation based on temperature differences rather than illumination differences. Specifically, four GO kernels, that is, K GO4 with considering sunlit/shaded vegetation and sunlit/shaded soil, K GO3 with considering sunlit/shaded soil and vegetation, K GO2 with considering vegetation and soil, and K GOg only considering the hottest sunlit soil, have been developed. By using a comprehensive simulated data set, their performances have been thoroughly evaluated and the comparison with K GOLSR has also been analyzed in depth. Results showed that (1) K GO4 had the highest accuracy and K GO3 was the second; in the case of only two available angles, K GOg performed best. (2) Variables such as component temperature, component emissivity, solar zenith angle, and the percentage of tree crown cover mainly affected the comparison result between K GOLSR and K GO2 ; K GOLSR would have a better performance for a scene with a stronger vegetation effect. Moreover, the best values of two structure characteristics, that is, the crown shape parameter b / r and relative height h / b , for these five kernels have been determined, which can provide instruction for practical application. Plain Language Abstract Land surface temperature is a key variable for a variety of geoscientific studies. However, because of the heterogeneity of land surface, this important parameter has a significant angular effect. Previous studies mainly learned from directional reflectance models. Therefore, in this study, we developed four geometric optical kernels for correcting directional effect of land surface temperature from the inherent characteristic of thermal radiation. These new kernels not only own clearer physical meaning but also have higher accuracies. Moreover, we also determined the best values of two structure characteristics to provide instruction for practical application.
关键词：thermal radiation directionality;geometric optical model;kernel function;component temperature difference;land surface temperature
