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@ARTICLE{Jantol:1017059,
      author       = {Jantol, Nela and Prikaziuk, Egor and Celesti, Marco and
                      Hernandez-Sequeira, Itza and Tomelleri, Enrico and
                      Pacheco-Labrador, Javier and Van Wittenberghe, Shari and
                      Pla, Filiberto and Bandopadhyay, Subhajit and Koren,
                      Gerbrand and Siegmann, Bastian and Legović, Tarzan and
                      Kutnjak, Hrvoje and Cendrero-Mateo, M. Pilar},
      title        = {{U}sing {S}entinel-2-{B}ased {M}etrics to {C}haracterize
                      the {S}patial {H}eterogeneity of {FLEX} {S}un-{I}nduced
                      {C}hlorophyll {F}luorescence on {S}ub-{P}ixel {S}cale},
      journal      = {Remote sensing},
      volume       = {15},
      number       = {19},
      issn         = {2072-4292},
      address      = {Basel},
      publisher    = {MDPI},
      reportid     = {FZJ-2023-03901},
      pages        = {4835 -},
      year         = {2023},
      abstract     = {Current and upcoming Sun‑Induced chlorophyll Fluorescence
                      (SIF) satellite products(e.g., GOME, TROPOMI, OCO, FLEX)
                      have medium‑to‑coarse spatial resolutions (i.e.,
                      0.3–80 km)and integrate radiances from different sources
                      into a single ground surface unit (i.e., pixel).
                      However,intrapixel heterogeneity, i.e., different soil and
                      vegetation fractional cover and/or different
                      chlorophyllcontent or vegetation structure in a fluorescence
                      pixel, increases the challenge in retrievingand quantifying
                      SIF. High spatial resolution Sentinel‑2 (S2) data (20 m)
                      can be used to better characterizethe intrapixel
                      heterogeneity of SIF and potentially extend the application
                      of satellite‑derivedSIF to heterogeneous areas. In the
                      context of the COST Action Optical synergies for
                      spatiotemporalSENsing of Scalable ECOphysiological traits
                      (SENSECO), in which this study was conducted, weproposed
                      direct (i.e., spatial heterogeneity coefficient, standard
                      deviation, normalized entropy, ensembledecision trees) and
                      patch mosaic (i.e., local Moran’s I) approaches to
                      characterize the spatialheterogeneity of SIF collected at
                      760 and 687 nm (SIF760 and SIF687, respectively) and to
                      correlateit with the spatial heterogeneity of selected S2
                      derivatives. We used HyPlant airborne imagery acquiredover
                      an agricultural area in Braccagni (Italy) to emulate
                      S2‑like top‑of‑the‑canopy reflectanceand SIF imagery
                      at different spatial resolutions (i.e., 300, 20, and 5 m).
                      The ensemble decision treesmethod characterized FLEX
                      intrapixel heterogeneity best (R2 > 0.9 for all predictors
                      with respect toSIF760 and SIF687). Nevertheless, the
                      standard deviation and spatial heterogeneity coefficient
                      using kmeansclustering scene classification also provided
                      acceptable results. In particular, the
                      near‑infraredreflectance of terrestrial vegetation (NIRv)
                      index accounted for most of the spatial heterogeneity
                      ofSIF760 in all applied methods (R2 = 0.76 with the standard
                      deviation method; R2 = 0.63 with the spatialheterogeneity
                      coefficient method using a scene classification map with 15
                      classes). The models developed for SIF687 did not perform as
                      well as those for SIF760, possibly due to the
                      uncertaintiesin fluorescence retrieval at 687 nm and the low
                      signal‑to‑noise ratio in the red spectral region.
                      Ourstudy shows the potential of the proposed methods to be
                      implemented as part of the FLEX groundsegment processing
                      chain to quantify the intrapixel heterogeneity of a FLEX
                      pixel and/or as a qualityflag to determine the reliability
                      of the retrieved fluorescence.},
      cin          = {IBG-2},
      ddc          = {620},
      cid          = {I:(DE-Juel1)IBG-2-20101118},
      pnm          = {2173 - Agro-biogeosystems: controls, feedbacks and impact
                      (POF4-217)},
      pid          = {G:(DE-HGF)POF4-2173},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:001084676300001},
      doi          = {10.3390/rs15194835},
      url          = {https://juser.fz-juelich.de/record/1017059},
}