Abstract
Abstract. Three-dimensional distribution of plant area density (PAD) was retrieved using airborne laser scanning (ALS) data. The calculation of PAD requires the number of laser-pulses intercepted by plant materials and which are not intercepted by trees (i.e., passed laser-pulses) for the spatial unit. To estimate the passed laser-pulses at a voxel (1-m voxel in this study), we traced every laser-return by using its flight line information. The assumption was that every laser-pulse traveled on the orthogonal line to flight line, meaning that the sensor mounted in the aircraft scanned perpendicularly to its flight line. Our function based on this assumption allowed PAD to be calculated. Consequently, we successfully obtained the PAD profiles at every 1-m voxel for the canopy area of 56 trees, which could be useful in the quantitative assessment of canopy structure at a broad scale.
Highlights
The horizontal and vertical structures of tree canopies provide important information to understand the functional characteristics and processes
The canopy structure is often quantified by leaf area index (LAI, the area of leaves per unit ground area), which is calculated by integrating leaf area density (LAD), the area of leaves per unit volume (Weiss et al, 2004)
This study proposed the voxel-based modeling methodology that could retrieve the 3-dimentional distribution of plant area density (PAD) from the airborne laser scanner (ALS) point-clouds data
Summary
The horizontal and vertical structures of tree canopies provide important information to understand the functional characteristics and processes. The coordinate of each laser-echo is important for the estimation of PAD from ALS data, because it means that the recorded position seems to be occupied with plant materials. It can be assumed that all laser-pulses fall from the zenith direction, i.e., laserechoes indicate the gap fraction on the vertical column (Morsdorf et al, 2006, Sasaki et al, 2008). This assumption is limited on the observation at small scan angle, or for the spatial unit of large area (i.e., plot-based) and thin layers (Figure 1) (Takeda et al, 2008). We attempted to make the calculation possible, by estimating the trace of each laser-return using the flight line information
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