以行道树无患子为研究目标，采用地面激光扫描(TLS)技术提取单木分回波点云数据。获取全波形数据、单目标数据、首次回波数据、其余次回波数据，建立基于多回波点云的算法，利用消光系数法提取不同投影分辨率0.01 m、0.02 m和0.03 m的的单株树叶面积指数(LAI)。利用2维影像数据数字半球影像(DHP)和LAI2200提取对应单株树的叶面积指数，进行比较分析，以检验其精度。结果表明：点云投影的分辨率与激光回波都对LAI有极显著影响，其中分辨率为0.02 m和0.03 m的估算结果与LAI2200所得估算结果相近，且差异不显著；单目标回波数据用于LAI的解算，可以同LAI2200的2维影像数据结果进行相互验证。使用单目标回波数据，0.02 m投影分辨率可以最大程度的保证单株LAI的精度，其与LAI2200测定的数据进行截距为0的线性回归，斜率达到0.827。本研究所做多回波地面激光数据计算叶面积指数的算法拓展了地面激光扫描的应用领域，为立木生长量信息准确提取和树木精确建模提供了重要的技术参考。

This study aimed to extract the Leaf Area Index (LAI) of individual trees through multi-return terrestrial laser point cloud data, including single target, first-return waveform, intermediate, and last target data.
The species was soapberry planted as street trees. An algorithm based on Beer-Lambert law was developed to divide return waveform, and the LAIs of individual trees with different projection resolutions of 0.01, 0.02, and 0.03 m were obtained. Two-dimensional digital hemispherical image data and LAI-2200 were used to extract the LAIs of corresponding single trees for accuracy comparison.
Result shows that the resolutions and multiple return waveforms have significant influence on LAI. The results with 0.02 m and 0.03 m resolutions are similar to those obtained with LAI2200, and the difference is insignificant. However, the single target waveform point cloud data are used for the LAI solution and can be mutually verified with the results of the 2D image data of LAI2200. The LAI value of single target waveform point cloud was calculated with Beer-Lambert at 0.02 m resolution, and the intercept measured by LAI2200 data was subjected to a linear regression with an intercept of 0 and slope of 0.827, which is close to 1.
Therefore, for the multi-return waveform ground laser scanning data, the single target waveform point cloud data with a projection resolution of 0.02 m can be used to obtain accurate LAI when using an extinction coefficient method. The algorithm for calculating the LAI based on multi-return waveform ground-based laser data in this study expands the application field of TLS and provides an important technical reference for the accurate extraction of the growth of standing trees and accurate tree modeling.