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@ARTICLE{Buman:906993,
      author       = {Buman, Bastian and Hueni, Andreas and Colombo, Roberto and
                      Cogliati, Sergio and Celesti, Marco and Julitta, Tommaso and
                      Burkart, Andreas and Siegmann, Bastian and Rascher, Uwe and
                      Drusch, Matthias and Damm, Alexander},
      title        = {{T}owards consistent assessments of in situ radiometric
                      measurements for the validation of fluorescence satellite
                      missions},
      journal      = {Remote sensing of environment},
      volume       = {274},
      issn         = {0034-4257},
      address      = {Amsterdam [u.a.]},
      publisher    = {Elsevier Science},
      reportid     = {FZJ-2022-01805},
      pages        = {112984 -},
      year         = {2022},
      abstract     = {The upcoming Fluorescence Explorer (FLEX) satellite mission
                      aims to provide high quality radiometric measurementsfor
                      subsequent retrieval of sun-induced chlorophyll fluorescence
                      (SIF). The combination of SIF withother observations
                      stemming from the FLEX/Sentinel-3 tandem mission holds the
                      potential to assess complexecosystem processes. The
                      calibration and validation (cal/val) of these radiometric
                      measurements and derivedproducts are central but challenging
                      components of the mission. This contribution outlines
                      strategies for theassessment of in situ radiometric
                      measurements and retrieved SIF. We demonstrate how in situ
                      spectrometermeasurements can be analysed in terms of
                      radiometric, spectral and spatial uncertainties. The
                      analysis of morethan 200 k spectra yields an average bias
                      between two radiometric measurements by two individual
                      spectrometersof $8\%,$ with a larger variability in
                      measurements of downwelling radiance $(25\%)$ compared to
                      upwellingradiance $(6\%).$ Spectral shifts in the
                      spectrometer relevant for SIF retrievals are consistently
                      below 1spectral pixel (up to 0.75). Found spectral shifts
                      appear to be mostly dependent on temperature (as measured
                      bya temperature probe in the instrument). Retrieved SIF
                      shows a low variability of $1.8\%$ compared with a
                      noisereduced SIF estimate based on APAR. A combination of
                      airborne imaging and in situ non-imaging
                      fluorescencespectroscopy highlights the importance of a
                      homogenous sampling surface and holds the potential to
                      furtheruncover SIF retrieval issues as here shown for early
                      evening acquisitions. Our experiments clearly indicate
                      theneed for careful site selection, measurement protocols,
                      as well as the need for harmonized processing. This workthus
                      contributes to guiding cal/val activities for the upcoming
                      FLEX mission.},
      cin          = {IBG-2},
      ddc          = {550},
      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:000798668300001},
      doi          = {10.1016/j.rse.2022.112984},
      url          = {https://juser.fz-juelich.de/record/906993},
}