Scaling up Solar-Induced Fluorescence from Leaf to Canopy in in a Conifer Forest with the Geometric Optical and Radiative Transfer Model

Abstract:

Gross primary production (GPP) prediction by global carbon cycle models has large uncertainties due to challenges in indirectly distinguishing GPP in measurements of CO2 fluxes, such that model parameters are poorly constrained. Solar-induced fluorescence (SIF) measurements appear strongly correlated with estimates of GPP. Measurements of SIF from flux towers and satellites like NASA’s Orbiting Carbon Observatory-2 and -3 (OCO-2 ad OCO-3) are being used to derive estimates of GPP. A few vegetation models have implemented SIF in their leaf biophysics in efforts to constrain photosynthesis parameters for prediction of GPP. However, these efforts have encountered challenges in scaling up leaf-level SIF to the canopy level in heterogeneous canopies, which have clumped foliage and vertical variation in foliage profiles. Geometric optical and radiative transfer (GORT) theory describes the heterogeneous distribution of light scattering elements within space. the GORT canopy model that simulates light absorption, albedo, and the bidrectional reflectance function distribution (BRDF). This study fuses the Simple Biosphere Model 3 (SiB3) leaf SIF model with the GORT BRDF model to scale the leaf level SIF to the canopy level. The canopy level of SIF prediction will be compared with the SIF measurements in Niwot Ridge site. The goal of this study is to understand the role of canopy structure on SIF measurements at various spatial and temporal scale.