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Assessing and correcting topographic effects on forest canopy height retrieval using airborne LiDAR data.

Duan Z, Zhao D, Zeng Y, Zhao Y, Wu B, Zhu J - Sensors (Basel) (2015)

Bottom Line: Finally, a height weighted correction method is applied to correct the topological effects.The method is applied to LiDAR data acquired in South China, and its effectiveness is tested using 41 field survey plots.The results show that the terrain impacts the canopy height of individual trees in that the downslope side of the tree trunk is elevated and the upslope side is depressed.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Digital Earth Science, Institute of Remote Sensing and Digital Earth (RADI), Chinese Academy of Science, Haidian District, Beijing 100094, China. zjj@mail.csu.edu.cn.

ABSTRACT
Topography affects forest canopy height retrieval based on airborne Light Detection and Ranging (LiDAR) data a lot. This paper proposes a method for correcting deviations caused by topography based on individual tree crown segmentation. The point cloud of an individual tree was extracted according to crown boundaries of isolated individual trees from digital orthophoto maps (DOMs). Normalized canopy height was calculated by subtracting the elevation of centres of gravity from the elevation of point cloud. First, individual tree crown boundaries are obtained by carrying out segmentation on the DOM. Second, point clouds of the individual trees are extracted based on the boundaries. Third, precise DEM is derived from the point cloud which is classified by a multi-scale curvature classification algorithm. Finally, a height weighted correction method is applied to correct the topological effects. The method is applied to LiDAR data acquired in South China, and its effectiveness is tested using 41 field survey plots. The results show that the terrain impacts the canopy height of individual trees in that the downslope side of the tree trunk is elevated and the upslope side is depressed. This further affects the extraction of the location and crown of individual trees. A strong correlation was detected between the slope gradient and the proportions of returns with height differences more than 0.3, 0.5 and 0.8 m in the total returns, with coefficient of determination R2 of 0.83, 0.76, and 0.60 (n = 41), respectively.

No MeSH data available.


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Distribution of terrain slope in the plots, average and maximum crown semidiameter. (a) terrain slope; (b) average and maximum crown semidiameter.
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sensors-15-12133-f002: Distribution of terrain slope in the plots, average and maximum crown semidiameter. (a) terrain slope; (b) average and maximum crown semidiameter.

Mentions: The ground-truth data were collected from 16 November 2012 to 9 December 2012. A total of 41 plots (30 × 30 m2), with most slopes between 8–40° (Figure 2a), were established, including four in coniferous forests, 22 in broadleaf forests, and 15 in mixed forests. Parameters measured mainly included: DBH of individual trees with a DBH >5 cm (DBH is measured from 1.3 m above ground), tree height, height to the first live branch, crown diameter, canopy density, slope gradient and aspect; all served as samples and evidence for LiDAR-based biomass inversion and biodiversity research. Plot area was measured by a forest compass combined with a measuring tape. Slope gradients were also determined by a forest compass. Angular point coordinates of plots were determined by the wide area differential signals of a Trimble3000 handheld GPS (Trimble, Sunnyvale, CA, USA), with sub-meter nominal accuracy. Individual tree DBHs were measured by a DBH tape; tree height and height to the first live branch were measured by a laser altimeter; crown semidiameter was measured in east-west and north-south directions with a measuring tape. Figure 2b shows that the average crown semidiameter in the plots was 1.6–5.2 m, and maximum crown semidiameter was 3.3–25.0 m, respectively.


Assessing and correcting topographic effects on forest canopy height retrieval using airborne LiDAR data.

Duan Z, Zhao D, Zeng Y, Zhao Y, Wu B, Zhu J - Sensors (Basel) (2015)

Distribution of terrain slope in the plots, average and maximum crown semidiameter. (a) terrain slope; (b) average and maximum crown semidiameter.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4507651&req=5

sensors-15-12133-f002: Distribution of terrain slope in the plots, average and maximum crown semidiameter. (a) terrain slope; (b) average and maximum crown semidiameter.
Mentions: The ground-truth data were collected from 16 November 2012 to 9 December 2012. A total of 41 plots (30 × 30 m2), with most slopes between 8–40° (Figure 2a), were established, including four in coniferous forests, 22 in broadleaf forests, and 15 in mixed forests. Parameters measured mainly included: DBH of individual trees with a DBH >5 cm (DBH is measured from 1.3 m above ground), tree height, height to the first live branch, crown diameter, canopy density, slope gradient and aspect; all served as samples and evidence for LiDAR-based biomass inversion and biodiversity research. Plot area was measured by a forest compass combined with a measuring tape. Slope gradients were also determined by a forest compass. Angular point coordinates of plots were determined by the wide area differential signals of a Trimble3000 handheld GPS (Trimble, Sunnyvale, CA, USA), with sub-meter nominal accuracy. Individual tree DBHs were measured by a DBH tape; tree height and height to the first live branch were measured by a laser altimeter; crown semidiameter was measured in east-west and north-south directions with a measuring tape. Figure 2b shows that the average crown semidiameter in the plots was 1.6–5.2 m, and maximum crown semidiameter was 3.3–25.0 m, respectively.

Bottom Line: Finally, a height weighted correction method is applied to correct the topological effects.The method is applied to LiDAR data acquired in South China, and its effectiveness is tested using 41 field survey plots.The results show that the terrain impacts the canopy height of individual trees in that the downslope side of the tree trunk is elevated and the upslope side is depressed.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Digital Earth Science, Institute of Remote Sensing and Digital Earth (RADI), Chinese Academy of Science, Haidian District, Beijing 100094, China. zjj@mail.csu.edu.cn.

ABSTRACT
Topography affects forest canopy height retrieval based on airborne Light Detection and Ranging (LiDAR) data a lot. This paper proposes a method for correcting deviations caused by topography based on individual tree crown segmentation. The point cloud of an individual tree was extracted according to crown boundaries of isolated individual trees from digital orthophoto maps (DOMs). Normalized canopy height was calculated by subtracting the elevation of centres of gravity from the elevation of point cloud. First, individual tree crown boundaries are obtained by carrying out segmentation on the DOM. Second, point clouds of the individual trees are extracted based on the boundaries. Third, precise DEM is derived from the point cloud which is classified by a multi-scale curvature classification algorithm. Finally, a height weighted correction method is applied to correct the topological effects. The method is applied to LiDAR data acquired in South China, and its effectiveness is tested using 41 field survey plots. The results show that the terrain impacts the canopy height of individual trees in that the downslope side of the tree trunk is elevated and the upslope side is depressed. This further affects the extraction of the location and crown of individual trees. A strong correlation was detected between the slope gradient and the proportions of returns with height differences more than 0.3, 0.5 and 0.8 m in the total returns, with coefficient of determination R2 of 0.83, 0.76, and 0.60 (n = 41), respectively.

No MeSH data available.


Related in: MedlinePlus