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Validation of biophysical produtcs from large swath sensors

Validation of biophysical produtcs from large swath sensors. F. Baret, M. Weiss*, O. Marloie, N. Bruguier, J.P. Guinot, B. Combal INRA CSE Avignon D. Allard INRA Biométrie Avi

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Validation of biophysical produtcs from large swath sensors

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  1. Validation of biophysical produtcs from large swath sensors F. Baret, M. Weiss*, O. Marloie, N. Bruguier, J.P. Guinot, B. Combal INRA CSE Avignon D. Allard INRA Biométrie Avi A. Begué, G. De Wispelaere, C. Lelong, V. Gond, CIRAD MontpellierM. Leroy, E. Mougin, CESBIO Toulouse J.P. Lagouarde, D. Guyon INRA Bordeaux J.L. Roujean CNRM Toulouse S. Rambal, H. Bohbot CEFE Montpellier T. Nilson, A. Kuusk Tartu Observatory * Détachée de Noveltis à l'INRA d'Avignon The project is supported by CNES

  2. Methodology: 5 steps • Définition of the spatial sampling strategy • 2. Local ground georeferenced measurements of LAI, fAPAR, fCover. • 3. Spatial Extension of local measurements using SPOT images • 4- Agregation to estimate the biophysical variables at the large swath sensors resolution, and the associated uncertainty. • 5- Evaluation of the accuracy of estimates over the ensemble of sites and dates available (including MODLAND) CEOS Frascati, 07/05/2001

  3. SITE DISTRIBUTION VALERI CEOS Frascati, 07/05/2001

  4. 2001 Schedule 2000: 4 sites for methodological developpements 2001: 14 opérational sites CEOS Frascati, 07/05/2001

  5. What we learned • Définition of the spatial sampling strategy • Method to extend local measurements to the whole site • LAI/fAPAR/fCover Measurements based on hemispherical photos • Aerosol optical depth measurements based on BF2 systems CEOS Frascati, 07/05/2001

  6. Spatial sampling strategy Continuous landscpe Discontinuous landscape 3 Km 3 Km N (=9) transects of 1km length 27 crosses of 12 points: short lags Spatial distribution and Representation of each class Visual notation every 1-4 metres Detailed measurements on a sub-sample Few transects: medium to long lags CEOS Frascati, 07/05/2001

  7. Spatial extension methods Results on Alpilles 2001, cross validation Direct regression Use of a SPOT image: Co-kriging CEOS Frascati, 07/05/2001

  8. Spatial extension methods Co-Kriging Ordinary Kriging LAI maps CEOS Frascati, 07/05/2001

  9. Kriging error Krigeage ordinaire Co-Krigeage Kriging Standard deviation of LAI CEOS Frascati, 07/05/2001

  10. Choice of the variogramme model Transects Crosses Cross validation CEOS Frascati, 07/05/2001

  11. Weight of the spatial information CEOS Frascati, 07/05/2001

  12. LAI, fAPAR, fCover measurements: Hemispherical photographs LAI2000 sampling • Advantages of hémispherical photos • Short vegetation measurements • Better spatial and directional sampling • Less sensitive to illumination conditions • Acces to clumpiness characteristics CEOS Frascati, 07/05/2001

  13. Aerosol Characterisation : BF2 Measurement of direct PAR irradiance • PAR transmittance related to aerosol optical thickness • Calibration based on Bouguer's line • Validation of the method based on 3 AERONET sites CEOS Frascati, 07/05/2001

  14. The Web site: www.avignon.inra.fr/valeri CEOS Frascati, 07/05/2001

  15. Conclusion • STATUS • Advances in methodological developments • 14 sites sampled in 2001 • Good collaboration with MODLAND (common site, data exchange) • PROBLEMS • Albédo, Chlorophyll? • Transfer function between reflectance and measurements? • Additional funding to go up to the validation of products: • ESA (MERIS) • PCRD • … CEOS Frascati, 07/05/2001

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