FluorWPS: A Monte Carlo ray-tracing model to compute sun-induced chlorophyll fluorescence of three-dimensional canopy

Authors: ZHAO, FENG - Beihang University; DAI, XU - Beihang University; VERHOEF, WOUT - University Of Twente; GUO, YIQING - Beihang University; TOL, CHRISTIAAN - University Of Twente; LI, YUGUANG - University Of Washington; Huang, Yanbo

Submitted to: Remote Sensing of Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/2016
Publication Date: 12/1/2016
Citation: Zhao, F., Dai, X., Verhoef, W., Guo, Y., Tol, C., Li, Y., Huang, Y. 2016. FluorWPS: A Monte Carlo ray-tracing model to compute sun-induced chlorophyll fluorescence of three-dimensional canopy. Remote Sensing of Environment. 187:385-399.

Interpretive Summary: Remote sensing of sun-induced chlorophyll fluorescence of plants is an emergening technology for studying natural resources and agricultural management. The mechanism of generation of sun-induced chlorophyll fluorescence of plants is necessary to study for better signal acquisition, processing and interpretation. Scientists at Beihang University, Beijing, China; University of Twente, Enschede, The Netherlands; University of New South Wales, Canberra, Australia; University of Washington, Seattle, WA, USA; and USDA-ARS Crop Production Systems Research Unit, Stoneville, MS, USA jointly proposed and evaluated a model to simulate radiative transfer of sun-induced chlorophyll fluorescence on three-dimensional canopy. The results indicate that the new model outperforms other established physically-based models and provides high accuracies of signal reconstruction from field measurements. The feature of the model’s plant canopy reconstruction from the radiative processes promises the model’s wide applications for in-depth studies of sun-induced chlorophyll fluorescence of plant canopy.

Technical Abstract: A model to simulate radiative transfer (RT) of sun-induced chlorophyll fluorescence (SIF) of three-dimensional (3-D) canopy, FluorWPS, was proposed and evaluated. The inclusion of fluorescence excitation was implemented with the ‘weight reduction’ and ‘photon spread’ concepts based on Monte Carlo ray-tracing technique. The radiation transfer of SIF in a 3-D canopy was simulated in a physically-based and rigorous way so that various contributions from the radiative process can be accurately quantified. The physical mechanism behind the spectral and angular distributions of canopy SIF was analyzed based on FluorWPS. SIF anisotropy is an intrinsic property of the vegetative surface and it can be significantly influenced by the canopy structure. The performance of the model was evaluated with field measurements and with systematic comparison with an established RT model of canopy SIF. Especially the detailed comparison with the RT model for four canopy scenes demonstrates that FluorWPS is capable of faithfully reproducing the spectral and angular distributions of SIF, with the coefficient of determination (R2) and root mean square error (RMSE) being higher than 0.92 and lower than 0.066 W·m-2·sr-1·nm-1, respectively, for the red peak, and higher than 0.92 and lower than 0.16 W·m-2·sr-1·nm-1 for the far-red peak. The independent nature of the model’s canopy realization from its radiative processes promises its wide applications for scientific investigations.