Tree height estimations for different forest canopies in natural secondary forests based on ULS, TLS and ultrasonic altimeter systems

doi:10.12302/j.issn.1000-2006.202009021

JOURNAL OF NANJING FORESTRY UNIVERSITY ›› 2021, Vol. 45 ›› Issue (4): 23-32.doi: 10.12302/j.issn.1000-2006.202009021

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Tree height estimations for different forest canopies in natural secondary forests based on ULS, TLS and ultrasonic altimeter systems

ZHAO Yinghui¹^,²(), YANG Haicheng¹, ZHEN Zhen¹^,²^,^*()

1. School of Forestry, Northeast Forestry University, Harbin 150040, China
2. Key Laboratory of Sustainable Forest Ecosystem Management-Ministry of Education, Northeast Forestry University, Harbin 150040, China

Received:2020-09-09 Accepted:2020-11-02 Online:2021-07-30 Published:2021-07-30
Contact: ZHEN Zhen E-mail:zyinghui0925@126.com;zhzhen@syr.edu

Abstract

Abstract:

【Objective】 A comparison of tree heights, estimated from different data sources for different forest canopies, was performed in natural secondary forests of Northern China to identify the optimal data source for different forest canopy layers. 【Method】 The study area, with a plot of 0.25 hm², was located in the Maoershan Forest Farm of the Northeast Forestry University. We conducted a performance comparison of terrestrial laser scanning (TLS), unmanned aerial vehicle laser scanning (ULS), and the Vertex IV ultrasonic instrument system in the estimation of individual tree heights. The forest canopy was stratified according to the canopy height distribution (CHD), and individual tree heights of different tree types (coniferous and broadleaved) were estimated and compared according to different canopy layers (overstory and understory). 【Result】 The threshold of canopy stratification calculated by CHD was 8.5 m. We also found that the outliers of tree heights mostly occurred in the overstory canopy, deciduous trees were more prone to outliers than coniferous trees, and ULS was more prone to outliers than TLS. Stratification of the forest canopy based on CHD can reflect the scope of tree height estimation using different data sources. In the overstory, the relative root mean square error (rRMSE) of tree height estimated by ULS was 2.56% lower than that estimated by TLS, while the rRMSE of coni-ferous tree height estimated by ULS was 2.68% lower than that of deciduous trees. ULS can only detect a small number of trees and had a higher rRMSE of 6.31% compared to TLS. Furthermore, the rRMSE of coniferous tree height estimated by TLS was 1.16% lower than that of deciduous trees. 【Conclusion】 For different canopy layers, the accuracy of conife-rous tree height was generally higher than that of deci-duous tree height. When both TLS and ULS can scan a single tree completely, both have the potential to accurately obtain the tree height. Most outliers of tree height were caused by deci-duous trees that had irregular or intertwined crowns. Most coniferous trees had few outliers in tree height due to their regular crown shapes. It is important to note that the stratification of the forest canopy based on CHD could reflect the scope of the applications of different data sources on the tree height estimation.

Key words: unmanned aerial vehicle laser scanning(ULS), terrestrial laser scanning(TLS), ultrasonic instrument systems, tree height, forest canopy, natural secondary forests

CLC Number:

S758

ZHAO Yinghui, YANG Haicheng, ZHEN Zhen. Tree height estimations for different forest canopies in natural secondary forests based on ULS, TLS and ultrasonic altimeter systems[J]. JOURNAL OF NANJING FORESTRY UNIVERSITY, 2021, 45(4): 23-32.

Figures/Tables 9

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References 38

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树木类型 tree types	株数 number of trees	统计特征 statistic feature	胸径/ cm DBH	树高/m tree height	冠幅/m crown width
针叶树 coniferous trees	144	最大值	25.90	15.40	5.87
		最小值	5.60	5.40	1.80
		平均值	14.13	10.71	3.42
		标准差	5.14	2.48	0.96
阔叶树 broadleaved trees	215	最大值	42.01	21.30	11.19
		最小值	5.00	4.90	1.25
		平均值	11.04	10.10	4.35
		标准差	6.19	3.03	1.71
合计 total	359	最大值	42.01	21.30	11.19
		最小值	5.00	4.90	1.25
		平均值	12.28	10.70	3.98
		标准差	5.98	3.02	1.52

3种数据源 three data sources	林冠上层 overstory canopy		林冠下层 understory canopy
3种数据源 three data sources	针叶树 coniferous trees	阔叶树 broadleaved trees	针叶树 coniferous trees	阔叶树 broadleaved trees
基于ULS数据的离群值 outliers based on ULS data	7	13	4	6
基于TLS数据的离群值 outliers based on TLS data	1	8	1	1
ULS和TLS离群值交集 intersection of outliers using ULS and TLS	-	3	-	-

冠层 canopy	树木类型 tree types	株数 number of trees	σ(RMSE)/ m	σ(rRMSE)/ %	σ(Bias)/ m	σ(rBias)/ %	R
林冠上层 the overstory canopy	针叶树 coniferous trees	96	0.41	3.44	-0.07	-0.57	0.97
	阔叶树 broadleaved trees	134	0.77	6.12	-0.34	-2.73	0.97
	合计 total	230	0.64	5.19	-0.22	-1.78	0.97
林冠下层 the understory canopy	针叶树 coniferous trees	1	-	-	-	-	-
	阔叶树 broadleaved trees	14	0.80	10.14	0.47	6.04	0.90
	合计 total	15	0.80	10.14	0.47	6.04	0.90
总计 total	针叶树 coniferous trees	97	0.41	3.44	-0.07	-0.57	0.97
	阔叶树 broadleaved trees	148	0.77	6.23	-0.31	-2.45	0.98
	合计 total	245	0.63	5.34	-0.20	-1.66	0.97

冠层 canopy	树木类型 tree types	株数 number of trees	σ(RMSE)/ m	σ(rRMSE)/ %	σ(Bias)/ m	σ(rBias)/ %	R
林冠上层 the overstory canopy	针叶树 coniferous trees	101	0.67	5.71	-0.37	-3.23	0.96
	阔叶树 broadleaved trees	126	1.02	8.40	-0.57	-4.70	0.97
	合计 total	227	1.02	7.75	-0.85	-6.50	0.95
林冠下层 the understory canopy	针叶树 coniferous trees	28	0.23	3.21	0.14	2.00	0.97
	阔叶树 broadleaved trees	25	0.33	4.37	0.16	2.22	0.93
	合计 total	53	0.28	3.83	0.16	2.18	0.96
总计 total	针叶树 coniferous trees	129	0.60	5.62	-0.27	-2.51	0.98
	阔叶树 broadleaved trees	151	0.95	8.30	-0.47	-4.07	0.98
	合计 total	280	0.81	7.26	-0.37	-3.36	0.98

冠层 canopy	树木类型 tree types	株数 number of trees	σ(RMSE)/m	σ(rRMSE)/%	σ(Bias)/m	σ(rBias)/%	R
林冠上层 the overstory canopy	针叶树 coniferous trees	83	0.67	5.68	-0.44	-3.73	0.93
	阔叶树 broadleaved trees	98	0.71	5.82	-0.42	-3.50	0.96
	合计 total	181	0.70	5.76	-0.44	-3.60	0.95
林冠下层 the understory canopy	针叶树 coniferous trees	1	-	-	-	-	-
	阔叶树 broadleaved trees	9	0.61	7.44	0.05	0.69	0.97
	合计 total	10	0.61	7.44	0.05	0.69	0.97
总计 total	针叶树 coniferous trees	84	0.67	5.68	-0.44	-3.73	0.93
	阔叶树 broadleaved trees	107	0.71	5.86	-0.41	-3.41	0.96
	合计 total	191	0.70	5.78	-0.43	-3.56	0.95

Tree height estimations for different forest canopies in natural secondary forests based on ULS, TLS and ultrasonic altimeter systems

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