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

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Methodology: 5 steps

1. 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)

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SITE DISTRIBUTION

VALERI

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2001 ScheduleSemaines 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50Alpilles AlpRomilly RomRoumanie Rou RouMali MalLandes Lan LanEstonie EstMontpellier MonBolivie BolArgentine ArgIndonesie IndGuyane Guy MexMexique

LAI 2000-VAL3 Alp Lan Ind Rom Est BolLAI 2000-CSE1 Alp Lan Ind Rom Mon Lan Mal Guy Arg MexLAI2000-CSE4 Rou Rou Mon Lan MalLAI2000-CESBIO EstLAI2000-CEFE Mon Guy Arg MexLAI2000-CIRAD Ind

Niko-CSE1 Alp Lan Rou Mon Bol Mal Guy Arg MexNiko-VAL2 Alp Rou Ind Rom Est LanNiko-VAL2 Bol Mal Guy Arg Mex

GPS-Mag1 Alp Rou RouRom Est Bol Mal ArgGPS-MLR2 Alp Rom MonGPS-VAL3 Ind Mal Guy Arg Mex

Photometre manuel Lan ArgBF2-CSE1 Alp Rou Mon LanBF2-VAL2 Ind Rom Est Bol Mal Guy Arg Mex

2000: 4 sites for methodological developpements2001: 14 opérational sites

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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

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Spatial sampling strategy

N (=9) transects of 1km length

Visual notation every 1-4 metres

Detailed measurements on a sub-sample

Continuous landscpe

27 crosses of 12 points: short lagsSpatial distribution and Representation of each classFew transects: medium to long lags

3 Km

3 K

m

Discontinuous landscape

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Spatial extension methods

Direct regression Use of a SPOT image:Co-kriging

Results on Alpilles 2001, cross validation

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Co-KrigingOrdinary Kriging

Spatial extension methods

LAI maps

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Kriging error

Co-Krigeage

Kriging Standard deviation of LAI

Krigeage ordinaire

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Choice of the variogramme model

Transects

Crosses

Cross validation

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Weight of the spatial information

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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

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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 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Measured Aerosol Optical Thickness

Est

imae

d A

eros

ol O

ptic

al T

hick

ness

Experimental data1 : 1 line 1 : 1 line

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The Web site: www.avignon.inra.fr/valeri

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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-…