Mana HAYASHI
A study on the canopy density estimation method based on the leaf area coverage using the reflection intensity of the full-waveform airborne LiDAR data
Kazuyoshi TAKAHASHI,Atsushi RIKIMARU
Currently, the crown density is used as the index of the blockage situation in forest. The amount of leaf in internal crown are ignored in this index.
The canopy density distribution represented by the leaf area coverage that we proposed represents the ground's surface projected area of the leaves and stem occupying the unit area. This index indicates the blockage situation of crown. We used the full-waveform airborne LiDAR data in order to estimate it.
We used the leaf area ratio for evaluation of the proposed method.
The leaf area ratio shows the leaf area per unit area from the 3D point data generated from the UAV Aerial pictures. It calculated as an index that reflects the leaf area and compared with the reflection intensity of the LiDAR data.
The reflection intensity depends on the following factors:
・Reflective surface occupancy in the footprint of LiDAR
・The reflectance of the reflecting surface
・Inclination angle of the reflecting surface
One of reflection point is a reflection from a plurality of leaf. Effect of inclination angle of the leaves are averaged.
The following two assumptions is provided to calculate the percentage of reflection intensity of the reflection point as share of the sum of the reflection intensity of the reflection point on the laser path (reflective surface occupancy ratio).
・Reflectance of the surfaces of leaves of the same tree are same.
・All reflection point on the laser path were reflected from the leaves in the same tree.
By the use of the reflective surface occupancy ratio, it can ignore the difference in reflectance of leaf in each tree species. It is possible to convert the reflected intensity area ratio. Analysis area is the location of the same crown at the UAV data and LiDAR data.
As a result, the correlation coefficient with the leaf area ratio was 0.7. Excluding the trees have obvious leaf surface situation differences in same species, the correlation coefficient between the reflection intensity was approximately 0.9. It shows that estimation of leaf area by the reflection intensity in there is a large difference between species of leaf surface situation inside crown is difficult.
In this study, the reflective surface occupancy ratio calculated using the reflection intensity that has been suggested is effective as an index that reflects the leaf area.
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