多波段波形激光雷达植被氮素含量垂直分布探测研究

Because of nitrogen is the element transferred easily, nitrogen vertical distribution is common on many vegetation. For the forests community, there are many different types of plants in the vertical direction, including trees, shrub, and grass. And the nitrogen concentration is also vertical distributed along the height. Considering the retrieval limitation relying only on solar illumination, the multispectral full-wave lidar will be studied for the retrieval of nitrogen concentration vertical distribution in the forests with three layers architecture. In the study, the forest radiative transfer model will be utilized for modeling laser signal intensity of every layer. Then, the sensitivity analysis of laser intensity to nitrogen concentration and other parameters in different layers will be carried out. Combining with the model simulation, the error distribution law will be set up to choose the optimal algorithm. Finally, the algorithm will be built and tested using the lidar remote sensing data and validated with ground measurements data in forests. The objective of this study was to discuss the method of extracting dynamic growth information for foliage vertical layers by canopy spectral reflectance for improving the accuracy of quantitative remote sensing canopy nitrogen concentration models, so as to provide a theoretic basis for monitoring the growth and development of vegetation.

由于氮素是"易转移"的元素，氮素的垂直梯度在植被上普遍存在；森林生态系统一般由林、灌、草等多种植被构成,呈现一定的垂直分层特征，其氮素含量也具有垂直分布特征更为明显。这种垂直分布特性对于更精确的生态系统评价和植被营养管理具有重要意义。考虑到只利用被动光学遥感反演植被生化组分垂直分布的局限性，本研究拟引入多波段的波形激光雷达（充分利用其多波段、部分穿透、全波形回波记录的特性）进行植被氮素浓度的垂直分布遥感监测模型研究。首先，探讨多波段激光雷达反演生化组分的机理，并基于辐射传输模型进行激光多层特征回波波形建模，模拟激光雷达回波与不同层植被氮素含量的关系，然后结合实测数据，筛选敏感波段，建立针对分层氮素浓度反演的主动遥感模型。其次，利用野外实测分层氮素含量及多波段波形激光雷达数据，进行模型驱动及优化算法的选择。最后，用实测数据进行植被氮素含量垂直分层分布的反演及验证。

氮素的垂直梯度在植被上普遍存在；森林生态系统一般由林、灌、草等多种植被构成,呈现一定的垂直分层特征，其氮素含量也具有垂直分布特征更为明显。这种垂直分布特性对于更精确的生态系统评价和植被营养管理具有重要意义。本研究拟引入多波段的波形激光雷达（充分利用其多波段、部分穿透、全波形回波记录的特性）进行植被氮素浓度的垂直分布遥感监测模型研究。首先，探讨多波段激光雷达反演生化组分的机理并进行了小光斑激光雷达反演模型建立，并基于辐射传输模型进行激光多层特征回波波形建模，模拟激光雷达回波与不同层植被氮素含量的关系，建立针对分层氮素浓度反演的主动遥感模型。最后，用实测数据进行植被氮素含量垂直分层分布的反演及验证。主要研究成果包括：1）基于小光斑激光雷达反演植被生化组分，建立了基于激光雷达回波强度和相位信息的植被氮素含量反演模型；2）基于植被指数的植被生化组分反演中的影响因素进行了试验与分析，指出植被指数可以消除距离和前后分别遮挡反射情况下的影响，但是不能消除叶片角度的影响；3）基于辐射传输理论模型、单次散射和激光雷达方程 ，建立了高光谱激光雷达模型，能够通过模型模拟植被叶面积指数和叶绿素等垂直方向变化带来的回波强度变化；4）搭建了面向植被理化参数垂直分布探测的4波段多光谱及32波段高光谱激光雷达仪器设备原型。