Model-based analysis of the relationship between sun-induced chlorophyll fluorescence and gross primary production for remote sensing applications

Abstract

Remote sensing of sun-induced chlorophyll fluorescence (SIF) is a novel optical tool for the assessment of terrestrial photosynthesis or gross primary production (GPP). Several recent studies have demonstrated the strong link between GPP and space-borne retrievals of SIF at broad scales. However, critical gaps remain between short-term small-scale mechanistic understanding and seasonal global observations. Here, we present a model-based analysis of the relationship between SIF and GPP across scales for diverse vegetation types and a range of meteorological conditions, with the ultimate focus on reproducing the environmental conditions during remote sensing measurements. The coupled fluorescence-photosynthesis model SCOPE is used to simulate GPP and SIF at the both leaf and canopy levels for 13 flux sites. Analyses were conducted to investigate the effects of temporal scaling, canopy structure, overpass time, and spectral domain on the relationship between SIF and GPP. The simulated SIF is highly non-linear with GPP at the leaf level and instantaneous time scale and tends to linearize when scaling to the canopy level and daily to seasonal. These relationships are consistent across a wide range of vegetation types. The relationship between SIF and GPP is primarily driven by absorbed photosynthetically active radiation (APAR), especially at the seasonal scale, although the photosynthetic efficiency also contributes to strengthen the link between them. The linearization of their relationship from leaf to canopy and averaging over time is because the overall conditions of the canopy fall within the range of the linear responses of GPP and SIF to light and the photosynthetic capacity. Our results further show that the top-of-canopy relationships between simulated SIF and GPP have similar linearity regardless of whether we used the morning or midday satellite overpass times. Field measurements confirmed these findings. In addition, the simulated red SIF at 685 nm has a similar relationship with GPP as that of far-red SIF at 740 nm at the canopy level. These findings provide model-based evidence to interpret remotely sensed SIF data and their relationship with GPP.3

Water, Energy, and Carbon with Artificial Neural Networks (WECANN): a statistically based estimate of global surface turbulent fluxes and gross primary productivity using solar-induced fluorescence

“…SIF retrievals are shown not to be strongly affected by cloud contamination and seasonal variabilities in aerosol optical depth . More recently, remotely sensed SIF retrievals have been used to successfully provide estimates of GPP in cropland and grassland ecosystems Zhang et al, 2016a). SIF retrievals are also integrated with photosynthesis estimates from the National Center for Atmospheric Research Community Land Model version 4 (NCAR CLM4), which result in significant improvement of the photosynthesis simulation (Lee et al, 2015).…”

SCOPE-Based Emulators for Fast Generation of Synthetic Canopy Reflectance and Sun-Induced Fluorescence Spectra

“…They have to be analyzed and consolidated before reaching conclusions whether emulators offer truly an attractive alternative over the original RTM. Specifically, SCOPE is currently used as baseline model in the FLEX End-to-End simulator [28] for delivering of R and SIF spectral outputs, and in the development of SIF retrieval methods [29] and subsequent interpretation towards photosynthetic activity [21,[30][31][32]. Thus, if evaluated as sufficiently accurate, an emulated version of SCOPE will greatly speed up all these processes.…”

Estimating Diurnal Courses of Gross Primary Production for Maize: A Comparison of Sun-Induced Chlorophyll Fluorescence, Light-Use Efficiency and Process-Based Models

“…There is also evidence indicating that the SIF and GPP relationship can be affected by various factors such as the rate of NPQ [61,87], light conditions [46,87], nutrient availability [61], water availability [85], temperature [23,46,68], and canopy structure [34]. Recent studies have suggested that there is a curvilinear relationship between instantaneous SIF and GPP due to the rate of photosynthesis saturated under high illumination, and this relationship tends to become linear when both SIF and GPP are temporally aggregated [28,34]. However, the saturation of GPP with APAR were not found in our experiment (Figure 4) as C4 species exhibit higher photosynthesis capacities at higher temperatures than C3 species.…”