森林冠层叶面积指数垂直分布地面间接测量及验证

Foliage profile of forest canopies controls the physiological and ecological process of forest canopies, such as microenvironment, and photosynthesis etc, it was widely used in forestry, ecology, and botany etc. A multi-spectral and full waveform terrestrial laser scanner would be developed based on a commercial full waveform terrestrial laser scanner(Riegl VZ400). And next a new method for the construction of isolated tree model and virtual forest environment was developed, which can conform to the main structural characteristic parameters and the vertical PAI and LAI distribution of trees. The typical virtual forest environment library with different forest stand characteristics, the distribution model of trees and terrain effects would be build based on the construction method of trees, and used as a union platform for validating the in situ indirect methods for obtaining the foliage profile of forest canopies. LAI-2000, DHP, MCI, inclined point quadrat method, MacArthur-Horn method, multi-spectral and full waveform terrestrial laser scanner method and the corresponding algorithms would be simulated under the typical virtual forest environment library, these indirect methods were validated next based on the true reference values of virtual forest environment. And the methods for removing the four sources of errors which were widely existed for the indirect methods of obtaining the foliage profile of forest canopies will be concluded, a new scheme for the measurement of foliage profile of forest canopies needed to be proposed at last.

森林冠层LAI垂直分布控制着森林冠层微环境及光合作用等生理生态过程，它在林学、生态学、植物学等领域均有着广泛的应用。本项目以商业化全波形地面激光雷达(Riegl VZ400）为基础，研制多光谱全波形地面激光雷达，开发可顾及树木冠层结构特征及LAI、PAI垂直分布的单树及虚拟森林环境构建方法，同时以此为基础形成具有不同林分特征、树木分布模式及地形条件的典型虚拟森林环境库，将其作为统一的森林冠层LAI垂直分布间接测量方法模拟验证平台。在虚拟森林环境下联合光线跟踪算法、投影算法、并行计算等手段实现LAI-2000、DHP、MCI、斜点样方法、MacArthur-Horn方法及多光谱全波形地面激光雷达六种间接测量方法及相关算法模拟，并以虚拟森林环境真实参考值开展验证分析，研究消除非光合作用组分影响、聚集效应、地形效应及观测方案误差来源的方法，最后提出高精度的森林冠层LAI垂直分布间接测量方案。

森林冠层 LAI控制着森林冠层微环境及光合作用等生理生态过程，它在遥感、林学、生态学、植物学等领域均有着广泛的应用。传统方法开展森林冠层LAI垂直分布测量具有投入大、效率低、难以实施等缺点及不足，而地面激光雷达具有记录植被冠层三维结构信息的特点，且其测量不易受天气条件影响，因此具有精确测量森林冠层LAI垂直分布的潜力。本项目引入高逼真度虚拟森林场景作为森林冠层LAI垂直分布测量及验证的平台。项目组提出了基于地面激光雷达的顾及冠层叶面积指数垂直分布特征的单株树木三维几何模型构建方法，考虑到单株树木三维几何模型建模精度及可靠性难以采取实测方法评估的现状，本项目引入高逼真度单株树木三维几何模型，并基于蒙特卡洛光线跟踪算法实现地面激光雷达测量方法模拟。基于模拟和实测（鸡蛋花树、芒果树和枫树）的典型单株树木地面激光雷达数据，选择树高、胸径、枝条半径变化函数以及PAD作为精度评价指标评价本课题提出的单株树木三维几何模型精度及可靠性，研究发现本文提出的方法其单株树木三维几何建模精度高。.基于高逼真度单株树木三维几何模型库构建了44个具有不同林分密度、树木分布模式、LAI及PAI垂直分布特征的虚拟森林场景库，并重点分析了四种基于地面激光雷达的森林冠层PAD测量方法（VCP、LAI-2000、MacArthur Horn和Calders）及斜点样方法PAD测量精度。研究结果表明，VCP方法森林冠层PAD测量精度受体元大小、叶倾角分布、扫描角分辨率以及冠层高度区间影响显著。对于VCP测量方法，以57.3°为中心天顶角进行扫描，可将叶倾角分布对测量结果精度影响降到最低，同时VCP方法测量精度随着冠层高度区间的增加而降低。间隙率方法测量结果受体元大小、冠层高度区间和扫描角分辨率的影响不显著，MacArthur Horn、LAI-2000、Calders三种间隙率方法测量结果与真实值相比，分别低估了79.24%、62.32%和45.84%。与斜点样方法和半球成像方法相比，地面激光雷达测量结果比斜点样方法、半球成像方法稳定，其PAD平均测量误差为27.73%。