非均质场景热辐射方向性模型构建与应用研究

Thermal radiation directionality is one of the bottlenecks in the improvement of the accuracy of land surface temperature (LST) product and the applications of LST product. This problem has been ignored in the operational algorithms of LST product and upwelling longwave radiation (ULR) product. Most of current directional thermal radiation models are designed for homogeneous scene, and thus is not feasible for the heterogeneous scenes, especially at the satellite pixel scale. A typical heterogeneous scene composed of vegetation, road and house endmembers will be taken as an example, and a new spatial heterogeneity expression method will be proposed to characterize the adjacency relationship between different endmembers. Based on the understanding of photon radiative transfer process within and among different endmembers, we intend to build a new directional thermal radiation model for typical heterogeneous scene which can consider the effect of spatial pattern, three dimensional structure and temperature distribution. After validating the new model using multi-scale observations, we attempt to analyze the error of ULR when using directional radiation temperature as input, and analyze the feasibility of the validation method which uses longwave radiation observations as input. This project is expected to become the bridge linking the research of thermal radiation directionality modeling and the research of LST retrieval. And the new model is expected to improve the accuracy of LST and ULR products.

热辐射方向性是制约当前地表温度产品精度提高及后续应用有效开展的瓶颈之一，地表温度产品及上行长波辐射产品的业务运行算法中均对该问题予以回避。现有的热辐射方向性模型多针对均质场景，对非均质场景刻画能力的欠缺在很大程度上限制了其在像元尺度上的应用。本项目尝试以植被、道路、房屋三种端元构成的典型非均质场景为例，提出可表征端元间邻接关系的空间异质性表达方法，探讨光子在端元内部及端元之间的辐射传输过程，构建考虑空间格局、三维结构和温度分布对热辐射影响的非均质场景热辐射方向性模型。在利用多尺度观测数据对模型进行验证的基础之上，尝试基于该模型深入分析方向辐射温度与半球辐射温度之间的差异。本项目有望成为链接热辐射方向性建模研究和地表温度反演研究的桥梁，有望进一步提高地表温度产品及上行长波辐射产品的精度。

本项目围绕非均质场景热辐射方向性模型构建与应用研究开展了三个方面的研究工作：（1）完成了现有不同地表（植被、水体、冰面、海面、雪面、土壤、城市）热辐射方向性模型的综述，这是热红外遥感领域第一次对地球表面所有地类进行全面的模型综述。针对现有均质场景模型的不足，发展了基于再碰撞概率的连续植被冠层方向发射率模型CE-P及方向亮度温度模型DBT-P，实现了各阶散射项的解析化分离并证明了在连续植被体系内考虑单次散射的可行性（2）完成了植被遥感建模中异质性研究进展的综述，梳理了空间格局指数、地统计学方法、及植被体系内部均匀-随机-聚集-垂直结构-斑块混合等异质性表达方法。发展了均匀-垄行-离散场景一体化热辐射方向性模型UFR及耦合能量平衡过程的非均质场景热辐射方向性模型TRGMEB和RAPIDEB，实现了考虑农田、道路、房屋等端元的非均质场景物理模型建模的突破。（3）提出了考虑聚集指数的异质性地表组分温度反演稳健方法，首创了非均质地表考虑热辐射方向性的地表上行长波辐射估算方法，基于航空多角度观测数据及地面长波辐射表实测数据的验证结果表明，最大可将估算精度显著提高约7.5W。项目执行期间，共发表论文19篇，其中SCI论文10篇，EI期刊论文4篇，EI会议论文5篇，完成了项目计划的指标。