Abstract
Sun-induced canopy chlorophyll fluorescence in both the red (FR) and far-red (FFR) regions was estimated across a range of temporal scales and a range of species from different plant functional types using high resolution radiance spectra collected on the ground. Field measurements were collected with a state-of-the-art spectrometer setup and standardized methodology. Results showed that different plant species were characterized by different fluorescence magnitude. In general, the highest fluorescence emissions were measured in crops followed by broadleaf and then needleleaf species. Red fluorescence values were generally lower than those measured in the far-red region due to the reabsorption of FR by photosynthetic pigments within the canopy layers. Canopy chlorophyll fluorescence was related to plant photosynthetic capacity, but also varied according to leaf and canopy characteristics, such as leaf chlorophyll concentration and Leaf Area Index (LAI). Results gathered from field measurements were compared to radiative transfer model simulations with the Soil-Canopy Observation of Photochemistry and Energy fluxes (SCOPE) model. Overall, simulation results confirmed a major contribution of leaf chlorophyll concentration and LAI to the fluorescence signal. However, some discrepancies between simulated and experimental data were found in broadleaf species. These discrepancies may be explained by uncertainties in individual species LAI estimation in mixed forests or by the effect of other model parameters and/or model representation errors. This is the first study showing sun-induced fluorescence experimental data on the variations in the two emission regions and providing quantitative information about the absolute magnitude of fluorescence emission from a range of vegetation types.
Highlights
Interest in remote sensing of sun-induced chlorophyll fluorescence emitted by terrestrial vegetation in the red (FR ) and far-red (FFR ) regions is motivated by the causal relation between fluorescence and actual plant photosynthesis [1].Under natural sunlight illumination, the amount of chlorophyll fluorescence emitted by terrestrial vegetation is a small fraction of the radiation reflected by a plant in the red and near-infrared spectral regions
As fluorescence emission is mainly driven by the magnitude of incident radiation, the comparison between different targets was performed by normalizing F by the incident radiation to get an apparent F yield (Fy)
The dataset presented in this contribution is of great importance for the characterization of fluorescence emission from different plant functional types with varying leaf and canopy characteristics, as well as the validation of the fluorescence maps derived from remote sensors with lower spatial resolution
Summary
Interest in remote sensing of sun-induced chlorophyll fluorescence emitted by terrestrial vegetation in the red (FR ) and far-red (FFR ) regions is motivated by the causal relation between fluorescence and actual plant photosynthesis [1].Under natural sunlight illumination, the amount of chlorophyll fluorescence emitted by terrestrial vegetation is a small fraction of the radiation reflected by a plant in the red and near-infrared spectral regions. Global maps of sun-induced chlorophyll fluorescence in the far-red region are becoming increasingly available from satellites [3,4,5] designed for atmospheric studies. Such instruments have spatial and temporal resolutions that are unsuited for vegetation studies [6]. This makes a proper validation of the fluorescence maps over terrestrial ecosystems not feasible. The ground-based characterization of different plant functional types at different spatial and temporal scales can be extremely useful for the evaluation of reliable ranges of variation for fluorescence retrieval and for a better understanding of the main factors inducing fluorescence modulation in both space and time
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