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@INPROCEEDINGS{Malenovsky:1047679,
      author       = {Malenovsky, Zbynek and Regaieg, Omar and Bendig, Juliane
                      and Siegmann, Bastian and Krämer, Julie and Lauret,
                      Nicholas and Buffat, Jim and Rascher, Uwe},
      title        = {{P}hysical modeling and scaling canopy far-red {SIF}
                      radiance down to leaf and photosystem fluorescence
                      efficiencies},
      reportid     = {FZJ-2025-04454},
      year         = {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.},
      month         = {Dec},
      date          = {2025-12-15},
      organization  = {American Geosciences Union, New
                       Orleans (USA), 15 Dec 2025 - 19 Dec
                       2025},
      subtyp        = {Invited},
      cin          = {IBG-2 / IAS-8},
      cid          = {I:(DE-Juel1)IBG-2-20101118 / I:(DE-Juel1)IAS-8-20210421},
      pnm          = {2173 - Agro-biogeosystems: controls, feedbacks and impact
                      (POF4-217) / 5112 - Cross-Domain Algorithms, Tools, Methods
                      Labs (ATMLs) and Research Groups (POF4-511)},
      pid          = {G:(DE-HGF)POF4-2173 / G:(DE-HGF)POF4-5112},
      typ          = {PUB:(DE-HGF)6},
      url          = {https://juser.fz-juelich.de/record/1047679},
}