冠层垂向异质性对冬小麦反射光谱及理化参数遥感估算的影响研究

The remote sensing technique is widely used and becoming increasingly important in crop status assessments (e.g., leaf area index, dry matter, nitrogen status, chlorophyll and water content), and the fundamental basis for this is the interrelationships between crop features and canopy reflectance characteristics. Crop canopies generally have a three-dimensional structure. The non-uniform vertical distributions of crop geometric structural, biochemical and physiological parameters result in large vertical heterogeneity in canopies. However, the factor of canopy vertical heterogeneity has been seldom taken into account carefully in remote estimations of crop variables, whether by empirical relationship models or the inversion algorithm for the using canopy reflectance models, which may affect the accuracy and practical stability of related results. The objective of the project is to study the vertical heterogeneous characteristics of wheat canopies, and their effects and mechanisms on canopy reflectance characteristics and the remote estimations of crop parameters. Based on field experiments, simulation analysis and multi-platform remote sensing observations, the main work of this project is as follows: (1) investigating the vertical heterogeneous characteristics of wheat canopies, their variations under different growth conditions and among different periods of the season, and their effects on crop status assessments; (2) revealing the effects and mechanisms of canopy vertical heterogeneity on canopy radiative transfer processes and reflectance spectra based on field data and scenarios simulation analysis; (3) exploring the effects and mechanisms of canopy vertical heterogeneity on the remote sensing modeling of crop variables, and then establishing the methods and models with strong stability and high accuracy by taking the factor of canopy vertical heterogeneity into account; (4) revealing the effects of canopy vertical heterogeneity on crop variables estimations from different remote sensing platforms such as near earth, unmanned aerial vehicle and satellite observations, by comparing the estimation results of models with and without considering canopy vertical heterogeneity. The expected outcomes of this project will be helpful to achieve a thorough knowledge of the interrelationships between crop features and canopy spectral characteristics, and to improve the accuracy and practical stability of crop status assessments by quantitative remote sensing methods.

遥感技术用于提取作物LAI、干物质、氮素、叶绿素、水分等理化参数的重要性已被普遍认可，其根本依据是作物特性与冠层反射光谱的内在联系。作物冠层由于几何结构和理化性质垂直分布差异而呈现垂向异质性。然而，目前作物理化参数遥感估算，无论基于经验统计法还是冠层反射模型反演法，均对冠层垂向异质性考虑不多，会影响模型估测精度和应用稳定性。本项目拟运用田间观测、模型模拟等手段，探究冠层垂向异质性对冬小麦反射光谱及理化参数遥感估算的影响和机理。主要内容为：①冠层垂向异质性特征及对作物整体生长状况表征的影响；②冠层垂向异质性对辐射传输过程及反射光谱的影响和机理；③冠层垂向异质性对作物理化参数遥感建模的影响和机理，构建考虑冠层垂直分布差异的估算方法和模型；④考虑冠层理化参数垂直分布差异前后不同遥感平台（近地、无人机、卫星）估测精度对比与验证。研究结果将有助于拓展作物遥感监测的理论认知深度，提高监测精度和稳定性。

遥感技术用于提取作物LAI、干物质、氮素、叶绿素、水分等理化参数的重要性已被普遍认可，其根本依据是作物特性与冠层反射光谱的内在联系。作物冠层几何结构及其生化组分是影响冠层光学特性的主要因素，其在冠层内的垂直分布差异而呈现的垂向异质性对冠层光谱反射和作物理化参数遥感建模有着重要影响。然而目前对此鲜有研究和考虑。鉴于此，本项目根据研究计划，运用田间试验观测和模型情景模拟等手段，主要开展了以下研究：①分析了冬小麦冠层几何结构参数（LAI、叶角）和生物理化参数（叶绿素、干物质、氮素、水分）的垂向异质分布特征以及各叶层各组分对作物整体状况表征的影响和作用；②基于冬小麦冠层多层辐射传输模型，采用情景模拟分析，揭示了冠层垂向异质性以及各叶层、穗组分对辐射传输过程（反射、透射、吸收）的影响，以及对冠层反射光谱及透射光谱的影响；③通过分析不同冠层垂向异质分布情景下冠层LAI、叶绿素、叶水、叶角等参数遥感建模常用自变量植被指数的变化差异阐释了冠层垂向异质性对冠层LAI、叶绿素、叶水、叶角等参数遥感建模的影响；④通过考虑冠层叶氮垂向异质分布特性构建了作物氮营养遥感诊断模型，并基于无人机遥感数据开展了比较验证，以实例阐释了考虑冠层叶氮垂向异质分布信息对于提升作物遥感氮营养监测诊断的重要作用。.在本项目的资助下，目前已发表学术论文8篇（其中SCI论文5篇），还有2篇SCI论文处于第三轮审稿中，4篇SCI/EI论文处于第一轮审稿中；授权发明专利1项；培养研究生3名，晋升研究员1名，晋升副教授1名；完成了项目研究内容和目标，取得了预期研究成果。