TY - JOUR
T1 - Characterizing the three-dimensional spatiotemporal variation of forest photosynthetically active radiation using terrestrial laser scanning data
AU - Ma, Lixia
AU - Zheng, Guang
AU - Ying, Qing
AU - Hancock, Steven
AU - Ju, Weimin
AU - Yu, Dongsheng
N1 - Funding Information:
Funding and resources for this research project came from the Key Research and Development Programs for Global Change and Adaptation (grant number NO. 2019YFA0606601), National Science Foundation of China (NSFC) (NSFC award #41771374 and #42001302). This research is also supported by the program B for Outstanding Ph.D. candidate of Nanjing University, and the “Ecological geological survey of Yudu area, Ganzhou” project of China Geological Survey (No. DD20190540). The support provided by the China Scholarship Council (CSC) to Lixia Ma during the visit at the University of Maryland is acknowledged. We want to thank Xiaofei Wang, Lu Lu, Binxiao Wu, Zengxin Yun, Hailong Xu, Jinglin Deng, Shihao Tian, Zhaoshang Xu, Jingyi Xia, and Yang Chen for their help in field data collection. Anonymous reviewers are appreciated for their valuable suggestions and comments to improve this manuscript significantly.
Publisher Copyright:
© 2021 Elsevier B.V.
PY - 2021/5/15
Y1 - 2021/5/15
N2 - The three-dimensional (3-D) spatiotemporal distribution of forest canopy photosynthetically active radiation (PAR) is a major determinant of within-crown variations of leaf photosynthesis and transpiration. However, it remains challenging to map the 3-D spatiotemporal distribution of PAR within and under the forest canopy due to the limited ability to capture the detailed 3-D structures of forest canopies.This study proposes a simple approach to estimate the 3-D spatiotemporal distribution of forest canopy PAR at a fine spatial resolution based on terrestrial laser scanner (TLS) data by characterizing difference in transfer of incident solar direct PAR and diffuse PAR and by considering the effect of the orientation angles of foliage elements on the 3-D distribution of direct PAR. Estimated PAR was validated using 10-minute PAR measurements from pyranometers at different locations within four forest plots, at which effective leaf area index (LAIe) ranged from 0.83–4.25. It showed that the proposed method captured 85% (N=2831, p<0.001) of the variations in the field pyranometer measurements. Furthermore, the proposed method was also applicable for estimating the vertical distribution of PAR (R2=0.95, N=15, p<0.001). Direct, diffuse, and total PAR exhibited similar vertical distributions changing with LAIe. It was shown that without differentiation of direct and diffuse PAR or ignoring effects of orientation angles of foliage elements may cause errors of about 20% in the estimated 3-D PAR distribution. Furthermore, the results indicated that the proposed method can be used to estimate the vertical distribution of PAR when the average neighbor point distance (NPD) is ≤20 cm. This proposed method will be usable for accurate separation of sunlit and shaded leaves and estimation of vertical distribution of PAR, which will benefit to reduce uncertainties in the estimation of terrestrial carbon fluxes and retrieval of vegetation structural and biochemical parameters.
AB - The three-dimensional (3-D) spatiotemporal distribution of forest canopy photosynthetically active radiation (PAR) is a major determinant of within-crown variations of leaf photosynthesis and transpiration. However, it remains challenging to map the 3-D spatiotemporal distribution of PAR within and under the forest canopy due to the limited ability to capture the detailed 3-D structures of forest canopies.This study proposes a simple approach to estimate the 3-D spatiotemporal distribution of forest canopy PAR at a fine spatial resolution based on terrestrial laser scanner (TLS) data by characterizing difference in transfer of incident solar direct PAR and diffuse PAR and by considering the effect of the orientation angles of foliage elements on the 3-D distribution of direct PAR. Estimated PAR was validated using 10-minute PAR measurements from pyranometers at different locations within four forest plots, at which effective leaf area index (LAIe) ranged from 0.83–4.25. It showed that the proposed method captured 85% (N=2831, p<0.001) of the variations in the field pyranometer measurements. Furthermore, the proposed method was also applicable for estimating the vertical distribution of PAR (R2=0.95, N=15, p<0.001). Direct, diffuse, and total PAR exhibited similar vertical distributions changing with LAIe. It was shown that without differentiation of direct and diffuse PAR or ignoring effects of orientation angles of foliage elements may cause errors of about 20% in the estimated 3-D PAR distribution. Furthermore, the results indicated that the proposed method can be used to estimate the vertical distribution of PAR when the average neighbor point distance (NPD) is ≤20 cm. This proposed method will be usable for accurate separation of sunlit and shaded leaves and estimation of vertical distribution of PAR, which will benefit to reduce uncertainties in the estimation of terrestrial carbon fluxes and retrieval of vegetation structural and biochemical parameters.
KW - Forest canopy
KW - Photosynthetically active radiation (PAR)
KW - Terrestrial laser scanning (TLS)
KW - Three-dimensional spatiotemporal distribution
U2 - 10.1016/j.agrformet.2021.108346
DO - 10.1016/j.agrformet.2021.108346
M3 - Article
AN - SCOPUS:85100671754
VL - 301-302
JO - Agricultural and Forest Meteorology
JF - Agricultural and Forest Meteorology
SN - 0168-1923
M1 - 108346
ER -