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Remote Sensing Technology and Application  2022, Vol. 37 Issue (5): 1071-1083    DOI: 10.11873/j.issn.1004-0323.2022.5.1071
    
Research on Individual Tree Volume Estimation Using Backpack LiDAR
Chao Ma1(),Huaguo Huang1,Xin Tian2(),Bingjie Liu1,Kunjian Wen1,Pengjie Wang2
1.Beijing Forestry University Forest Resources and Environmental Management National Forest and Grass Bureau Key Laboratory,Beijing 100083,China
2.Institute of Forest Resource Information Techniques,Chinese Academy of Forestry,Beijing 100091,China
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Abstract  

Backpack Laser Scanning (BLS) is a potential tool in forest resource survey, but shows much uncertainty for the extraction accuracy of single-tree volume and forest stand volume in complex topographic circumstances. Using BLS point cloud data from the Gaofeng Forest Farm in Guangxi Province, this study implemented the estimation of single-tree volume and sample plot volume by random forest approach. First, individual tree segmentation was conducted using the BLS point cloud data, 8 characteristic parameters were extracted including Diameter at Breast Height (DBH), Tree Height (Htree), Crown Diameter (CD), Crown Area (CA), Crown Volume (CV), Canopy Cover (CC), Gap Fraction (GF), and Leaf Area Index (LAI), and 56 stratification height indicators were calculated (height percentage, cumulative height percentage, coefficient of variation, canopy undulation rate, etc.). Then, an individual treee volume estimation model was developed using the random forest technique, and the prediction accuracy of various parameter combinations was investigated. The results showed that: (1) modeling with only 8 characteristic parameters of an individual tree structure indicated an estimated accuracy of R2=0.83、RMSE=0.097 m3; (2) modeling estimation accuracy was improved with the addition of the layered height index: R2=0.87、RMSE=0.087 m3; (3) the Boruta algorithm for variable screening reduced the input parameters from 64 to 52, with little difference in estimation accuracy: R2=0.87, RMSE=0.087 m3; (4) the estimation accuracy of sample plot volume was R2=0.97, RMSE=0.703 m3·ha-1. The results suggested the application potential to use the BLS point cloud for individual tree volume estimation and the sample volume by random forest algorithm.

Key words:  Volume      Backpack laser scanning      Random forest      Boruta algorithm     
Received:  08 December 2021      Published:  13 December 2022
ZTFLH:  TN958.98  
Corresponding Authors:  Xin Tian     E-mail:  machao31@126.com;tianxin@ifrit.ac.cn
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Articles by authors
Chao Ma
Huaguo Huang
Xin Tian
Bingjie Liu
Kunjian Wen
Pengjie Wang

Cite this article: 

Chao Ma,Huaguo Huang,Xin Tian,Bingjie Liu,Kunjian Wen,Pengjie Wang. Research on Individual Tree Volume Estimation Using Backpack LiDAR. Remote Sensing Technology and Application, 2022, 37(5): 1071-1083.

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http://www.rsta.ac.cn/EN/10.11873/j.issn.1004-0323.2022.5.1071     OR     http://www.rsta.ac.cn/EN/Y2022/V37/I5/1071

Fig.1  Distribution map of sample plots in the study area
样地编号

平均胸径

/(cm)

平均树高

/(m)

蓄积量

/(m3·hm-2)

单木株数坡度坡向样地类型
A124.1831.88465.39294.34桉树林
A221.8725.71341.063227.75西北桉树林
A2111.1013.91112.485827.22西南桉树林
A611.7613.78153.246144.41西南桉树林
AS115.3117.08356.586335.87西南桉树杉木混交林
AS216.2317.81389.976330.09西北桉树杉木混交林
AS322.6628.34197.721628.83桉树杉木混交林
AS512.6313.41101.802014.95桉树杉木混交林
AS712.8215.94114.484525.26西南桉树杉木混交林
S11117.7412.18157.852532.87西南杉木林
S217.9013.86182.852634.40杉木林
S324.9516.74258.342354.48西南杉木林
S522.1016.07351.774235.90西南杉木林
S627.2016.8579.30637.84西南杉木林
S717.8113.4978.771728.28西南杉木林
S818.8913.34133.152239.20西南杉木林
S925.0617.22108.041038.64杉木林
Table 1  Sample plots information summary table
性能指标参数性能指标参数
激光器Velodyne VLP-16×2激光波长903 nm
LiDAR精度±3 cm扫描频率600 000 pts/s
相对精度3 cm水平视场角0°—360°
绝对精度5 cm垂直视场角-90°—90°
重量9.4 kg电池5 700 mAh
尺寸908 mm×300 mm×333 mm工作时间~2 h
激光扫描距离100 m工作温度-10 ℃—50 ℃
Table 2  LiBackpack DGC50 scanning system
Fig.2  Collection route planning
Fig.3  Flow chart of individual tree stock volume estimation
变量名称含义计算公式
Hcv变异系数Hcv=(Hstd/Hmean)×100% (5)
Hadd平均绝对偏差Haad=1ni=1nZi-Hmean (6)
Hcrr冠层起伏率Hcrr=(Hmean-Hmin)/(Hmax-Hmin) (7)
HAIHIQR累积高度百分位数四分位数间距HAIHIQR=HAIH75%-HAIH25% (8)
HIQR高度百分位数四分位数间距HIQR=H75%-H25% (9)
Hsq二次幂平均Hsq=(i=1nZi2)/n (10)
Hcmc三次幂平均Hcmc=(i=1nZi3)/n3 (11)
Hk峰度Hk=i=1n(Zi-Hmean)4(n-1)Hstd4 (12)
Hske偏斜度(偏态)Hk=i=1n(Zi-Hmean)3(n-1)Hstd3 (13)
Table 3  Calculation formula of height variable
序号变量名称含义
1Htree通过点云提取的单木树高
2DBH点云提取的单木胸径
3CD通过点云提取的单木冠幅直径
4CA通过点云提取的单木冠幅面积
5CV通过点云提取的单木冠幅体积
6CC郁闭度
7GF间隙率
8LAI叶面积指数
Table 4  Input individual tree structure variable
Fig.4  Evaluation indicators of model 1
Fig.5  Optimal ntree Parameter of model 1
Fig.6  Estimation individual tree stock volume with model 1
Fig.7  Box plot of variable importance
输入变量名变量含义变量个数输入变量名变量含义变量个数
CC郁闭度1HIQR高度百分位数四分位数间距1
LAI叶面积指数1Hk峰度1
Hmm中位数绝对偏差的中位数1Hske偏斜度(偏态)1
Hmax最大值1HAIHIQR累积高度百分位数四分位数间距1
Hmean平均值1DBH单木胸径1
Hmedian中位数1Htree树高1
Hstd标准差1CD冠幅直径1
Hvar方差1CA冠幅面积1
Hz平均绝对偏差1CV冠幅体积1
Hcrr冠层起伏率1DM

密度变量

拒绝DM1和DM3

8
Hsq二次幂平均1H%

高度百分位数

拒绝H1%和H5%

13
Hcmc三次幂平均1HAIH%

累积高度百分位数

拒绝HAIH1%,HAIH5%,HAIH10%,HAIH20%,HAIH30%和HAIH40%

9
Hcv变异系数1
Table 5  Results of variable filtering
Fig.8  The importance of filtering variables
Fig.9  Evaluation indicators of modeling
Fig.10  Optimal ntree parameter of modeling
Fig.11  Estimation individual tree stock volume with Model 2
Fig.12  Estimation individual tree stock volume with Model 3
建模训练结果建模验证结果
序号R2RMSE/(m3)序号R2RMSE/(m3)
10.980.03610.860.086
20.980.03620.870.088
30.980.03630.810.096
40.980.03440.810.118
50.980.03650.820.091
60.970.03760.910.072
70.980.03670.860.077
80.980.03680.850.09
90.980.03690.860.083
100.980.036100.890.078
Table 6  Results of Ten-fold modeling
Fig.13  Results of Ten-fold modeling
样地编号

实测蓄积量

/(m3·hm-2)

模型估测蓄积量

/(m3·hm-2)

实测与估测蓄积量之差

/(m3·hm-2)

A1465.39456.918.48
A2341.06341.75-0.69
A21112.48151.40-38.92
A6153.24172.97-19.73
AS1356.58375.63-19.05
AS2389.97407.07-17.1
AS3197.72197.290.43
AS5101.8089.5012.3
AS7114.48142.61-28.13
S111157.85133.8923.96
S2182.85184.52-1.67
S3258.34241.7816.56
S5351.77328.8522.92
S679.3063.2916.01
S778.7774.514.26
S8133.15132.890.26
S9108.04102.065.98
Table 7  Sample field volume estimation
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