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Lars Eklundh

Professor

Personal photograph

Calibrating vegetation phenology from Sentinel-2 using eddy covariance, PhenoCam, and PEP725 networks across Europe

Author

  • Feng Tian
  • Zhanzhang Cai
  • Hongxiao Jin
  • Koen Hufkens
  • Helfried Scheifinger
  • Torbern Tagesson
  • Bruno Smets
  • Roel Van Hoolst
  • Kasper Bonte
  • Eva Ivits
  • Xiaoye Tong
  • Jonas Ardö
  • Lars Eklundh

Summary, in English

Vegetation phenology obtained from time series of remote sensing data is relevant for a range of ecological applications. The freely available Sentinel-2 imagery at a 10 m spatial resolution with a ~ 5-day repeat cycle provides an opportunity to map vegetation phenology at an unprecedented fine spatial scale. To facilitate the production of a Europe-wide Copernicus Land Monitoring Sentinel-2 based phenology dataset, we design and evaluate a framework based on a comprehensive set of ground observations, including eddy covariance gross primary production (GPP), PhenoCam green chromatic coordinate (GCC), and phenology phases from the Pan-European Phenological database (PEP725). We test three vegetation indices (VI) — the normalized difference vegetation index (NDVI), the two-band enhanced vegetation index (EVI2), and the plant phenology index (PPI) — regarding their capability to track the seasonal trajectories of GPP and GCC and their performance in reflecting spatial variabilities of the corresponding GPP and GCC phenometrics, i.e., start of season (SOS) and end of season (EOS). We find that for GPP phenology, PPI performs the best, in particular for evergreen coniferous forest areas where the seasonal variations in leaf area are small and snow is prevalent during wintertime. Results are inconclusive for GCC phenology, for which no index is consistently better than the others. When comparing to PEP725 phenology phases, PPI and EVI2 perform better than NDVI regarding the spatial correlation and consistency (i.e., lower standard deviation). We also link VI phenometrics at various amplitude thresholds to the PEP725 phenophases and find that PPI SOS at 25% and PPI EOS at 15% provide the best matches with the ground-observed phenological stages. Finally, we demonstrate that applying bidirectional reflectance distribution function correction to Sentinel-2 reflectance is a step that can be excluded for phenology mapping in Europe.

Department/s

  • Dept of Physical Geography and Ecosystem Science
  • BECC: Biodiversity and Ecosystem services in a Changing Climate
  • MERGE: ModElling the Regional and Global Earth system

Publishing year

2021-07

Language

English

Publication/Series

Remote Sensing of Environment

Volume

260

Document type

Journal article

Publisher

Elsevier

Topic

  • Physical Geography

Keywords

  • Europe
  • EVI2
  • Gross primary production (GPP)
  • NDVI
  • PEP725
  • PhenoCam
  • Plant phenology index (PPI)
  • Sentinel-2
  • Vegetation phenology

Status

Published

Project

  • Copernicus High-Resolution Vegetation Phenology and Productivity

ISBN/ISSN/Other

  • ISSN: 0034-4257