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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/amt-2019-384
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2019-384
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 22 Jan 2020

Submitted as: research article | 22 Jan 2020

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This preprint is currently under review for the journal AMT.

Improved SIFTER v2 algorithm for long-term GOME-2A satellite retrievals of fluorescence with a correction for instrument degradation

Erik van Schaik1,*, Maurits L. Kooreman2,*, Piet Stammes2, L. Gijsbert Tilstra2, Olaf N. E. Tuinder2, Abram F. J. Sanders2,4,5, Willem W. Verstraeten1,2,3, Ruediger Lang5, Alessandra Cacciari5, Joanna Joiner6, Wouter Peters1,7, and K. Folkert Boersma1,2 Erik van Schaik et al.
  • 1Meteorology and Air Quality group, Wageningen University, 6700 AA Wageningen, The Netherlands
  • 2SatelliteObservations Department, Royal Netherlands Meteorological Institute, De Bilt, 3730 AE, The Netherlands
  • 3Royal Meteorological Institute of Belgium (KMI), Ringlaan 3, 1180, Ukkel, Belgium
  • 4Institute of Environmental Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany
  • 5EUMETSAT, EUMETSAT-Allee 1, 64295 Darmstadt, Germany
  • 6NASA Goddard Space Flight Center, Greenbelt, MD, United States
  • 7University of Groningen, Centre for Isotope Research, 9747 AG Groningen, The Netherlands
  • *These authors contributed equally to this work.

Abstract. Solar-induced fluorescence (SIF) data from satellites are increasingly used as a proxy for photosynthetic activity by vegetation, and as a constraint on gross primary production. Here we develop an improved retrieval algorithm to retrieve mid-morning (09:30 hrs local time) SIF estimates on the global scale from GOME-2 sensor on the Metop-A satellite (GOME-2A) for the period 2007–2019. Our new SIFTER v2 algorithm improves over a previous version by using a narrower spectral window that avoids strong oxygen absorption and is less sensitive to water vapour absorption, by constructing stable reference spectra from a 6-year period (2007–2012) of atmospheric spectra over the Sahara, and by applying a latitude-dependent zero-level adjustment that accounts for biases in the data product. We generated stable, good-quality SIF retrievals between January 2007 and June 2013, when GOME-2A degradation in the near infrared was still limited. After the narrowing of the GOME-2A swath in July 2013, we characterized the throughput degradation of the level-1 data in order to derive reflectance corrections and apply these for the SIF retrievals between July 2013 and December 2018. SIFTER v2 data compares well with the independent NASA v2.8 data product. Especially in the evergreen tropics, SIFTER v2 no longer shows the underestimates against other satellite products that were seen in SIFTER v1. The new data product includes uncertainty estimates for individual observations, and is best used for mostly clear-sky scenes, and when spectral residuals remain below a certain spectral autocorrelation threshold. Our results support the use of SIFTER v2 data to be used as an independent constraint on photosynthetic activity on regional to global scales.

Erik van Schaik et al.

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Erik van Schaik et al.

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Short summary
With our improved algorithm we have generated a stable, long-term dataset of fluorescence measurements from the GOME-2A satellite instrument. In this study we determined a correction for the degradation of GOME-2A in orbit, and applied this correction along with other improvements to our SIFTER v2 retrieval algorithm. The result is a coherent dataset of daily and monthly averaged fluorescence values for the period 2007–2020 to track worldwide changes in photosynthetic activity by vegetation.
With our improved algorithm we have generated a stable, long-term dataset of fluorescence...
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