Characterizing the three-dimensional spatiotemporal variation of forest photosynthetically active radiation using terrestrial laser scanning data

The three-dimensional (3-D) spatiotemporal distribution of forest canopy photosynthetically active radiation (PAR) is a major determinant within-crown variations leaf photosynthesis and transpiration. However, it remains challenging to map the 3-D PAR within under due limited ability capture detailed structures canopies.This study proposes simple approach estimate at fine spatial resolution based on terrestrial laser scanner (TLS) data by characterizing difference in transfer incident solar direct diffuse considering effect orientation angles foliage elements PAR. Estimated was validated using 10-minute measurements from pyranometers different locations four plots, which effective area index (LAIe) ranged 0.83–4.25. It showed that proposed method captured 85% (N=2831, p<0.001) field pyranometer measurements. Furthermore, also applicable for estimating vertical (R2=0.95, N=15, p<0.001). Direct, diffuse, total exhibited similar distributions changing with LAIe. shown without differentiation or ignoring effects may cause errors about 20% estimated distribution. results indicated can be used when average neighbor point distance (NPD) ≤20 cm. This will usable accurate separation sunlit shaded leaves estimation PAR, benefit reduce uncertainties carbon fluxes retrieval vegetation structural biochemical parameters.