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| Home > Publications database > Physical modeling and scaling canopy far-red SIF radiance down to leaf and photosystem fluorescence efficiencies |
| Home > Publications database > Physical modeling and scaling canopy far-red SIF radiance down to leaf and photosystem fluorescence efficiencies |
| Conference Presentation (Invited) | FZJ-2025-04454 |
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2025
Abstract: Remotely sensed far-red solar-induced fluorescence (SIF) is increasingly used as a proxy for modeling vegetation photosynthetic activity and gross primary production. However, the apparent top-of-canopy (TOC) SIF signal is strongly affected by non-physiological but physical factors, e.g., canopy structure, leaf and ground or atmospheric optical properties. This work demonstrates different TOC SIF normalization approaches, removing the confounding factors and extracting the physiologically relevant part of remotely-sensed SIF.Scaling TOC SIF down to the leaf emission efficiency requires estimation of the SIF escape fraction from the canopy (Fesc). Several optical indices characterizing canopy scattering of far-red SIF radiance were developed as proxies of Fesc. We tested performance of FCVI and two hyperspectral forms of NIRv (i.e., NIRvH1 and NIRvH2) using nadir airborne SIF of summer barley crops. Modeling in 3D Discrete Anisotropic Radiative Transfer (DART) suggested that the most accurate Fesc is estimated with NIRvH1. Consequently, the SIF normalization using NIRvH1 was found to have a superior performance over NIRvH2 and FCVI. Yet, when applied to the experimental drone and airborne nadir canopy SIF data, the obtained leaf chlorophyll fluorescence efficiencies of both NIRvH1 and FCVI were highly similar (R2 = 0.93).To scale far-red TOC SIF down to emissions from photosystems inside chloroplasts (i.e., PSI and PSII), we developed a novel method estimating the fluorescence quantum efficiency (FQE) based on an efficient DART-Lux bidirectional Monte-Carlo photon path tracing. The steady-state FQE is estimated through optimizing the DART-simulated TOC SIF against corresponding field/airborne measurements. When applied on in-situ measurements acquired with the Fluorescence Box (FloX) system, the retrieved FQE diurnal courses correlated significantly with the PSII photosynthetic yield measured by a MiniPAM active fluorometer (r = 0.87, R2 = 0.76 before and r = -0.82, R2 = 0.67 after 2.00 PM). After application on images from the airborne HyPlant spectrometer, the per-pixel FQE estimates formed narrow bell-shaped (near-Gaussian) histograms with a low coefficient of variation, indicating the reduction of spatial heterogeneity in the input TOC SIF radiance caused by confounding factors.
Keyword(s): Earth, Environment and Cultural Heritage (1st)
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