基于偏振遥感技术反演植被特征参数研究

Vegetation is a sensitive indicator of many ecosystem properties that influence energy balance, climate, hydrology, and biogeochemical cycling. During the past several decades, the tools for vegetation remote sensing have evolved significantly, because there is a correlation between the properties of vegetation cover and its spectral reflectance obtained via field measurements or remote-sensing platforms. Light scattered from surfaces is partly polarized, which has implications for remote sensing of vegetation. However, most of the study focused on the polarization of single leaf and vegetation cover, there is a little concern on the relation between polarization information and vegetation parameters. The goal of this study is to retrieve vegetation parameter (leaf inclination angle and chlorophyll content) basing on the polarized remote sensing method. First, we will study the influence of underlying surfaces on the polarization of single leaf and vegetation canopy, which is basing on the laboratory analysis, the field measurements and modeling. Second, we will characterize the contribution of the underlying surfaces on the total polarization from vegetation leaf and canopy, and separate the polarized portion and unpolarized portion from the total reflectance of vegetation leaf and canopy. Finally, retrieving the structural parameter of vegetation canopy (leaf inclination angle) using the polarized portion, and coupling unpolarized portion with photometric model to retrieve the biochemical parameter of vegetation leave and canopy (chlorophyll content). The polarization study present here, in comparison with existing inversion results of vegetation parameter, may be important for deepening our understanding of the polarization properties of vegetation canopy.

植被是地—气系统能量交换及维持辐射平衡的关键因子，同时也是反映全球气候变化的敏感指标，光学遥感为系统监测地表植被状况提供了可靠技术手段。其中，偏振信息已经成为光学遥感研究过程中不可或缺的一维信息，但是关于植被偏振特性的研究主要集中在单个叶片以及植被本身，并没有系统考虑植被的偏振特性以及如何利用偏振技术对植被特征参数进行反演，阻碍了其在植被监测方面的发展。本项目以“下垫面—植物叶片—植被冠层”偏振特性的关系为主线，以室内分析、野外试验以及模拟计算为主要技术手段。分析下垫面对叶片偏振特性，以及不同下垫面如何通过叶片对整个植被偏振特性的影响。阐明下垫面偏振的贡献，将植被反射过程中的偏振与非偏振部分分离。并通过模型参数量化植被结构特征参数(叶片倾斜角度)与偏振部分之间的关系；耦合光强反射模型与非偏振部分，反演植被生化特征参数(叶绿素含量)。最终实现利用偏振遥感技术反演植被特征参数的目标。

偏振信息已经成为植被光学遥感研究过程中不可或缺的一维信息，本研究系统考虑了植被的偏振特性以及如何利用偏振技术对植被特征参数进行反演。项目首先，以“下垫面—植物叶片—植被冠层”偏振特性的关系为主线，以室内分析、野外试验以及模拟计算为主要技术手段。分析了下垫面对叶片偏振特性，以及不同下垫面如何通过叶片对整个植被偏振特性的影响，发现，即使在叶片尺度下垫面的对偏振反射特性的影响就已经很小了；随后，基于斯托克斯参量结果，阐明了下垫面偏振的贡献，将植被反射过程中的偏振与非偏振部分进行了分离。最后，通过模型参数量化植被结构特征参数(叶片倾斜角度)与偏振部分之间的关系；并且实现了耦合光强反射模型与非偏振部分，同时基于非偏振信息反演植被生化特征参数(叶绿素含量)。最终实现了利用偏振遥感技术反演植被特征参数的目标。