Xiaoyang Zhang, Mark A. Friedl, and Crystal B. Schaaf Journal of Geophysical Research, 2006

Transcription

1 Global vegetation phenology from Moderate Resolution Imaging Spectroradiometer (MODIS): Evaluation of global patterns and comparison with in situ measurments Xiaoyang Zhang, Mark A. Friedl, and Crystal B. Schaaf Journal of Geophysical Research, 2006 Céline Dillmann, Armin Komposch, Fabio Fässler

2 Introduction Objectives of the paper: Test formerly developed remote sensing method to monitor vegetation phenonology Comparing new remote sensing data (MODIS) to in situ measurments Describe global patterns of phenology with this method Relevance? Céline Dillmann, Armin Komposch, Fabio Fässler

3 Methods MODIS (Moderate-resolution Imaging Spectroradiometer): sensor on satellite EVI (Enhanced Vegetation Index) AVHRR (Advanced Very High Resolution Radiometer) NDVI (Normalized Difference Vegetation Index) Céline Dillmann, Armin Komposch, Fabio Fässler

4 Methods NDVI= ρ NIR ρ red / ρ NIR + ρ red EVI= G ρ NIR ρ red / ρ NIR + C 1 ρ red C 2 EVI uses more spectral bands than NDVI, does not saturate as easy as the NDVI Céline Dillmann, Armin Komposch, Fabio Fässler

5 Methods Models Fitting pairs of logistic models to EVI values Modified after Zhang et al Céline Dillmann, Armin Komposch, Fabio Fässler

6 Methods Models Fitting pairs of logistic models to EVI values Modified after Zhang et al Céline Dillmann, Armin Komposch, Fabio Fässler

7 Methods Models Fitting pairs of logistic models to EVI values Modified after Zhang et al Céline Dillmann, Armin Komposch, Fabio Fässler

8 Methods Models Fitting pairs of logistic models to EVI values Modified after Zhang et al Céline Dillmann, Armin Komposch, Fabio Fässler

9 Methods Models Fitting pairs of logistic models to EVI values Modified after Zhang et al Céline Dillmann, Armin Komposch, Fabio Fässler

10 Methods In Situ measurements 3 sites Harvard Forest (UK) Hubbard Brook Forest (USA) Plantwatch Dataset (Canada) Similar but not identical data collected à different evaluations Céline Dillmann, Armin Komposch, Fabio Fässler

11 Results Harvard Forest (UK) 3-4 days difference greenness max. when 84-90% of leafs reached final size onset of G de 10 corresponds days difference to onset of leaf senescence (1% coloured leafs) Zhang et al Céline Dillmann, Armin Komposch, Fabio Fässler

12 Results Hubbard Brook Forest (USA) days difference Zhang et al Céline Dillmann, Armin Komposch, Fabio Fässler

13 Results Plantwatch Dataset (Canada) Strong correlation between first bloom and MODIS G in (R 2 =0.6) Zhang et al Céline Dillmann, Armin Komposch, Fabio Fässler

14 Results / Discussion - MODIS transition dates agree well with in situ observations - Start vs. End of growing season - Method performs well & yields realistic results - More field data required: vegetation / land cover rarely uniform Céline Dillmann, Armin Komposch, Fabio Fässler

15 Results Céline Dillmann, Armin Komposch, Fabio Fässler

16 Results / Discussion Global application geographically and ecologically realistic Use for understanding and modelling of effects of climatic variability on ecosystem processes. Land-use Agricultural land: phenological behaviour differs from natural vegetation Céline Dillmann, Armin Komposch, Fabio Fässler

17 Personal Assessment + Comparison of remote sensing data with in situ measurements + careful handling of satellite data à correction for climatic effects etc. - Choice of in situ measurement sites unclear à Satellite data indeed allow to monitor vegetation phenology at a global scale! Céline Dillmann, Armin Komposch, Fabio Fässler

18 References Zhang, X., M. A. Friedl, C. B. Schaaf, A. H. Strahler, J. C. F. Hodges, F. Gao, B. C. Reed and A. Huete (2003). "Monitoring vegetation phenology using MODIS." Remote Sensing of Environment 84(3): Zhang, X., M. A. Friedl and C. B. Schaaf (2006). "Global vegetation phenology from Moderate Resolution Imaging Spectroradiometer (MODIS): Evaluation of global patterns and comparison with in situ measurements." Journal of Geophysical Research: Biogeosciences 111(G4): G Céline Dillmann, Armin Komposch, Fabio Fässler