地基激光雷达反演树木叶面积参数方法

胡容海; 邢煜振

doi:10.11728/cjss2023.06.2023-0078

地基激光雷达反演树木叶面积参数方法

doi: 10.11728/cjss2023.06.2023-0078 cstr: 32142.14.cjss2023.06.2023-0078

中国科学院大学资源与环境学院　北京　100049
北京燕山地球关键带国家野外科学观测研究站　北京　101408

基金项目: 国家自然科学基金项目（42271393），中国科学院青年创新促进会和中央高校基本科研业务费专项资金项目共同资助

详细信息

作者简介:

胡容海：E-mail：huronghai@ucas.ac.cn

中图分类号: TP79
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出版历程
- 收稿日期: 2023-06-20
- 修回日期: 2023-08-11
- 网络出版日期: 2023-11-29

Retrieval methods for Tree Leaf Area Parameters Based on Terrestrial Laser Scanning

College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049
Beijing Yanshan Earth Critical Zone National Research Station, Beijing 101408

摘要

摘要: 叶面积指数（Leaf Area Index, LAI）是表征植被冠层结构的核心参数，叶面积指数的间接测量一直是植被遥感的一项重要研究内容。地基激光雷达（Terrestrial Laser Scanning, TLS）以其高效、精细的三维观测能力被广泛用于叶面积指数的反演研究，同时地基激光雷达也为反演更精细的叶面积参数，例如叶面积体密度（Foliage Area Volume Density, FAVD）的三维分布提供了可能性。从方法论角度出发，对基于地基激光雷达反演叶面积参数的主要方法，不同方法的优势、局限性和影响因素进行分析。现有反演方法可分为四类：基于间隙率的方法、基于接触频率的方法、基于计算机图形学理论的方法以及基于生态生理学模型的方法。基于地基激光雷达的叶面积参数反演也从样方尺度叶面积指数向更精细的单木尺度叶面积垂直剖面（Vertical Foliage Profile, VFP）和体素尺度叶面积体密度发展。在此过程中，聚集效应、非均一路径长度和遮挡效应是影响测量精度的重要因素，需要进一步的研究和校正。
- 叶面积参数 /
- 地基激光雷达 /
- 间隙率 /
- 接触频率 /
- 体素
Abstract: Leaf Area Index (LAI) is a key parameter that characterizes the structure of vegetation canopies, and the indirect measurement of LAI has always been an important research topic in vegetation remote sensing. Terrestrial Laser Scanning (TLS), with its efficient and precise three-dimensional observation capability, has been widely used for LAI estimation. At the same time, TLS provides possibilities for the inversion of more refined leaf area parameters, such as the three-dimensional distribution of Foliage Area Volume Density (FAVD). This paper reviews the main methods for retrieving leaf area parameters based on TLS from a methodological perspective, discussing their advantages, limitations, and influencing factors. The indirect measurement of leaf area parameters based on TLS can be classified into four categories: the gap fraction-based method, the contact frequency-based method, the computer graphics theory-based method, and the ecophysiological model-based method. These methods differ in theoretical foundations, data organization, etc., and are suitable for the retrieval of various leaf area parameters at different scales. Among them, the mainstream approach currently relies on the measurement and analysis of gap fraction, and it has evolved into three categories based on different forms of point cloud organization: 2D images, pulses, and voxels. Methods based on contact frequency, computer graphics theory, and ecophysiological models are also emerging, providing new avenues for leaf area parameter inversion and can be further optimized to improve the accuracy and efficiency of LAI estimation. Existing methods have basically covered the inversion of various leaf area parameters at different scales. From stand-scale LAI to more refined individual-tree-scale Vertical Foliage Profile (VFP) and voxel-scale FAVD, leaf area parameter inversion based on TLS continues to advance in a refined and three-dimensional direction. In this process, clumping effects, non-uniform path lengths, and occlusion effects are important factors that affect measurement accuracy and require further research and calibration.
- Leaf area parameter /
- Terrestrial laser scanning /
- Gap frequency /
- Contact frequency /
- Voxel

HTML全文

图 1 立方体体素（a）与球形体素（b）

Figure 1. Cube voxel (a) and spherical voxel (b)

下载: 全尺寸图片幻灯片

图 2 路径长度与自由路径长度。（a）路径长度（红色虚线）：不考虑命中植被元素条件下，光束通过体素的路径长度。（b）自由路径长度（红色虚线）：在最终命中植被元素之前光束实际探索的路径长度

Figure 2. Path length and free path length. (a) Path length (red dotted line): the length of the paths of beams through the voxels in case of absence of hit. (b) Free path length (red dotted line): the length of the paths actually explored by beams before eventual hit of vegetation element

下载: 全尺寸图片幻灯片

表 1 不同的叶面积参数缩写及含义

Table 1. Abbreviations and meanings of different leaf area parameters

叶面积参数	缩写	含义
叶面积（Leaf Area）	LA	所有叶片表面积的一半，常用于表征单木
叶面积指数（Leaf Area Index）	LAI	单位水平地表面积上所有叶片表面积的一半
有效叶面积指数（Effective Leaf Area Index）	LAIe	由Beer定律直接估算，未校正聚集效应的叶面积指数
真实叶面积指数（True Leaf Area Index）	LAIc	由Beer定律估算并校正聚集效应的叶面积指数
叶面积体密度（Foliage Area Volume Density）	FAVD	单位体积内单面叶面积总和，其在高度上的积分为叶面积指数
叶面积垂直剖面（Vertical Foliage Profile）	VFP	以LAI或者FAVD表征冠层垂直方向上不同分层内叶面积差异

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表 2 遮挡体素判定指标及处理方法

Table 2. Indicator and processing methods for occlusion voxels

遮挡体素判定指标	代表文献	遮挡体素处理方法	代表文献
最小探测脉冲数量	[15]	分配同层非遮挡体素的FAVD平均值	[15, 75]
最小可信间隙分数	[73]	分配所有非遮挡体素的FAVD平均值	[70]
脉冲探测到的体素体积比	[16, 70]	基于光传输模型，根据到达遮挡体素的阳光量分配FAVD	[16]
		基于非遮挡体素FAVD与高度等参量构建的经验关系	[70]

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表 3 基于地基激光雷达的叶面积参数反演方法

Table 3. Leaf area parameter inversion methods based on TLS

理论机理	数据组织	方法概述	尺度	参数	代表文献
Beer定律	2D图像	经投影等操作转DHP图像	林分	LAIc	[13, 33, 57, 59]
	脉冲	点云切片计算RDI(Beer定律)	林分	LAIe	[32, 61]
		点云切片计算RDI(间隙大小分布法)	单木	LAIc	[24–26]
		构建树冠包络(路径长度分布模型)	单木	LA	[14, 64]
	体素	分层体素数量比计算间隙率（空/总）	单木	VFP	[29]
	体素	体素内脉冲追踪	体素	FAVD	[15, 27, 40]
斜点样方	体素	分层体素数量比计算接触频率（叶/总）	单木	VFP	[79, 82]
		体素内脉冲追踪（平均路径长度）	体素	FAVD	[84]
		体素内脉冲追踪（平均自由路径长度）	体素	FAVD	[16, 86]
计算机图形学	点	特定点空间分辨率的代表面积	单木	LA	[17]
计算机图形学	点	Delaunay三角网组织点云并计算面积	单木	LA	[18]
生态生理学	点	构建异速生长回归方程	单木	LA	[19]

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表 4 联合多站数据方式及适用范围

Table 4. Approaches for joint multi-station data and their applicability

联合层次	联合方式	适用方法	代表文献
点云层面	多站点云合并	基于同层体素数量比计算间隙率/接触频率	[79]
		Delaunay三角网组织点云并计算面积
		构建异速生长回归方程
间隙率层面	多站间隙率取平均	Beer定律下基于脉冲的方法	[61]
结果层面	动态选取优势站数据	Beer定律下基于脉冲的方法	[16]
	动态选取优势站数据	体素内脉冲追踪	[16]
	多站结果取平均	Beer定律下基于脉冲的方法	[25]
	多站结果取平均	体素内脉冲追踪计算间隙率	[25]
	多站结果加权平均	Beer定律下基于脉冲的方法	[14]
	多站结果加权平均	体素内脉冲追踪计算间隙率	[14]
	多站结果加和	体素内脉冲追踪计算接触频率（平均自由路径长度）	[86]

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