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@ARTICLE{Liu:866591,
      author       = {Liu, Xinjie and Guanter, Luis and Liu, Liangyun and Damm,
                      Alexander and Malenovský, Zbyněk and Rascher, Uwe and
                      Peng, Dailiang and Du, Shanshan and Gastellu-Etchegorry,
                      Jean-Philippe},
      title        = {{D}ownscaling of solar-induced chlorophyll fluorescence
                      from canopy level to photosystem level using a random forest
                      model},
      journal      = {Remote sensing of environment},
      volume       = {231},
      issn         = {0034-4257},
      address      = {Amsterdam [u.a.]},
      publisher    = {Elsevier Science},
      reportid     = {FZJ-2019-05672},
      pages        = {110772 -},
      year         = {2019},
      abstract     = {Solar-induced chlorophyll fluorescence (SIF), an
                      electromagnetic signal that can potentially indicate
                      vegetation photosynthetic activity, can be retrieved from
                      ground-based, airborne and satellite measurements. However,
                      due to the scattering and re-absorption effects inside the
                      leaves and canopy, SIF measured at the canopy level is only
                      a small part of the total SIF emission at the photosystem
                      level. Therefore, a downscaling mechanism of SIF from the
                      canopy level to the photosystem level is important for
                      better understanding the relationship between SIF and the
                      vegetation gross primary production (GPP). In this study,
                      firstly, we analyzed the canopy scattering effects using a
                      simple parameterization model based on the spectral
                      invariant theory. The probability for SIF photons to escape
                      from the canopy was found to be related to the anisotropic
                      spectral reflectance, canopy interception of the upward
                      solar radiation, and leaf absorption. An empirical approach
                      based on a Random Forest (RF) regression algorithm was
                      applied to downscale SIF constrained by the red, red-edge
                      and far-red anisotropic reflectance. The RF was trained
                      using simulations conducted with the Soil Canopy
                      Observation, Photochemistry and Energy fluxes (SCOPE) model.
                      The performance of the SIF downscaling method was evaluated
                      with SCOPE and Discrete Anisotropic Radiative Transfer
                      (DART) model simulations, ground measurements and airborne
                      data. Results show that estimated SIF at the photosystem
                      level matches well with simulated reference data, and the
                      relationship between SIF and photosynthetically active
                      radiation absorbed by chlorophyll is improved by SIF
                      downscaling. This finding in combination with other
                      evaluation criteria suggests the downscaling of canopy SIF
                      as an efficient strategy to normalize species dependent
                      effects of canopy structure and varying solar-view
                      geometries. Based on our results for the SIF-APAR
                      relationship, we expect that such normalization approaches
                      can be helpful to improve estimates of photosynthesis using
                      remote sensing measurements of SIF.},
      cin          = {IBG-2},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IBG-2-20101118},
      pnm          = {582 - Plant Science (POF3-582)},
      pid          = {G:(DE-HGF)POF3-582},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000484643900067},
      doi          = {10.1016/j.rse.2018.05.035},
      url          = {https://juser.fz-juelich.de/record/866591},
}