Abstract
In order to retrieve gap fraction, leaf inclination angle, and leaf area index (LAI) of subtropical forestry canopy, here we acquired forestry detailed information by means of hemispherical photography, terrestrial laser scanning, and LAI-2200 plant canopy analyzer. Meanwhile, we presented a series of image processing and computer graphics algorithms that include image and point cloud data (PCD) segmentation methods for branch and leaf classification and PCD features, such as normal vector, tangent plane extraction, and hemispherical projection method for PCD coordinate transformation. In addition, various forestry mathematical models were proposed to deduce forestry canopy indexes based on the radiation transfer model of Beer-Lambert law. Through the comparison of the experimental results on many plot samples, the terrestrial laser scanner- (TLS-) based index estimation method obtains results similar to digital hemispherical photograph (HP) and LAI-2200 plant canopy analyzer taken of the same stands and used for validation. It indicates that the TLS-based algorithm is able to capture the variability in LAI of forest stands with a range of densities, and there is a high chance to enhance TLS as a calibration tool for other devices.
Highlights
The forest has an irreplaceable status in improving the Earth’s environment of human habitation and slowing down global environmental degradation trend
We presented a series of image processing and computer graphics algorithms that include image and point cloud data (PCD) segmentation methods for branch and leaf classification and PCD features, such as normal vector, tangent plane extraction, and hemispherical projection method for PCD coordinate transformation
Zheng and Moskal [13] presented a new voxel-based method with line quadrat direction to retrieve the biophysical characteristics of the forest canopy including extinction coefficient, gap fraction, and overlapping effect along the direction of the line quadrat and estimated effective leaf area (ELA) from terrestrial laser scanning (TLS) point cloud data
Summary
The forest has an irreplaceable status in improving the Earth’s environment of human habitation and slowing down global environmental degradation trend. Zheng and Moskal [13] presented a new voxel-based method with line quadrat direction to retrieve the biophysical characteristics of the forest canopy including extinction coefficient, gap fraction, and overlapping effect along the direction of the line quadrat and estimated effective leaf area (ELA) from TLS point cloud data. The experimental result showed that CanSPART mathematical model performed better in clumped canopies than a simple exponential model [17] Another method combining beer laws and using least square fitting techniques to reconstruct the normal vectors is presented, so it can indirectly and nondestructively retrieve foliage elements’ orientation and distribution from PCD obtained by using a terrestrial laser scanning (TLS) approach [18]. In the section of experiments and results, we compared three methods in many aspects to illustrate the effectiveness of our TLS-based method and provide concluding remarks for future work
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