山区地表短波与长波辐射组网验证及其时空尺度扩展研究

Land surface radiation budget is one of the hotspots in global change research. Clouds and terrain are two key factors influencing the accuracy of space-based surface radiation derivations. Although many efforts have been made to quantify the influence of cloud and topography on radiation, the existing research completely ignores the coupling effect of cloud and terrain on surface radiation. More importantly, the validation on mountainous regions as well as the issues of spatial and temporal scales of radiation have not been effectively solved, which seriously hinders the progress of space-based radiation balance studies. To solve the above problems, this study first realizes the cloud and terrain coupling modeling by considering cloud and shadow location correction, cloud-terrain-shadow relationship and the effect of cloud distribution on radiation, and the shortwave and longwave radiation over rugged terrain are then derived. To verify and improve the inversion algorithm, and to get rid of the defects of the serious lack of mountain radiation measurement stations over the globe, a scheme of validation network over mountainous regions are proposed, based on which, the derived radiation can be validated..based on the above verification network and derived radiation from space, a study of spatio-temporal scale expansion and scale effect at mountainous regions will be carried out. In addition to improving the retrieval accuracy of topographic radiation, this study can refine the surface radiation retrieval system over mountainous areas in three aspects: cloud - terrain coupling effect, validation at rugged terrain and spatial - temporal scale expansion, which will definitely push forward the development of the remote sensing radiation balance study.

地表辐射收支是全球变化研究的热点之一，云和地形是影响其遥感估算精度的两大关键因素。虽然针对性的研究越来越多，但现有研究完全忽略了云和地形对地表辐射的耦合影响，而且，山区辐射量验证以及辐射量的时空尺度问题一直没得到有效解决，严重阻碍了辐射平衡遥感的发展，行业认可度也较低。针对以上不足，本项目首先从云和阴影位置校正、云-地形-阴影的关系及云分布对辐射影响等角度实现云和地形耦合影响建模，进而准确反演山区短波与长波辐射；为检验和改进遥感反演算法、摆脱当前全球严重缺乏山区辐射观测站点的缺陷，提出了山区辐射组网验证方案，对山区辐射进行综合验证；基于上述验证网和遥感反演的辐射数据，结合CERES、FY-4数据开展山区地表辐射的时空尺度扩展和尺度效应研究。除了提高山区辐射反演精度，本研究还能在云-地形耦合效应、山区辐射验证和时空尺度扩展三个全新方面完善山区地表辐射反演体系，将有力推动辐射平衡遥感的发展。

山区的辐射收支是全球辐射收支的重要组成部分，同时，也是当前辐射平衡研究中不确定性最大的因素之一。山区辐射遥感估算面临的主要问题包括：（1）山区辐射站点观测匮乏，难以满足山区验证的需要；（2）适合遥感大面积快速、高精度反演的模型处于起步阶段，山区地表短波及长波辐射量的准确遥感估算仍具有较大挑战；（3）不同于水平地表，山区辐射量的时间和空间尺度扩展更加复杂，目前仍缺乏有效解决方案。针对上述问题，本研究开展了3大研究内容，即，云和地形耦合影响下地表短波和长波辐射建模、山区地表短波和长波辐射真实性检验组网方案设计与验证以及山区地表辐射的尺度扩展与尺度效应分析。. 通过研究，项目在青藏高原地区建立了包括四个观测站的短波及长波辐射综合验证网络；开发了考虑云及地形耦合效应的全天候条件下水平地表短波和长波辐射一体化新型反演算法，实现了地表短波下行总辐射、直射辐射、光合有效辐射（PAR）总量、PAR直射分量的同步反演，并改进了全天候地表长波辐射的反演算法；在原有基于DEM的山区模型基础上，构建了面向遥感像元尺度的短波和长波辐射快速地形校正模型(P-SWTRM、P-LWTRM)；基于辐射日变化规律模型，研发了瞬时地表短波和长波辐射的时间尺度扩展算法，实现了从瞬时辐射到多时间尺度平均辐射的准确估算；同时，充分考虑山区对辐射时空尺度的影响，建立了山区辐射时空尺度扩展方法。研究成果为山区辐射平衡遥感、全球辐射收支与气候变化相互作用等研究提供了方法以及科学参考。