1. Validation of CYCLOPES, MODIS & MERIS PRODUCTS
M. Weiss, F. Baret, K. Pavageau, P. Bicheron, M. Huc, D. Béal, W.Wang
10/03/2005
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2. Objectives= to validate LAI, fAPAR, fCover
Consistency between products (relative validation) ?
Consistency with ground truth (absolute validation) ?
Relative validation
Inter-comparison
Absolute Validation
Good repartition in space
(BELMANIP)
Temporal monitoring
(Weekly or decadal data)
Few points
Bad repartition in space
Bad repartition in time
Error quantification
(rms)
No error quantification
Use the two ways to get « the best evaluation »
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3. Problems associated with inter-comparison
Product definition (effective LAI or true LAI, instantaneous fAPAR at satellite overpass….)
Temporal composition : CYCLOPES = decade, MODIS= week
The « Footprint » : the size of the two objects must be the same
Geo-location : same geographic position (cartographic projection, sensor geo-location error, GPS measurement error,…)
Sensor PSF : the measured signal for a given pixel correspond to the pixel itself + its environment
Attenuating PSF + Geo location effect : Site size = 3kmx3km
Footprint: CYCLOPES = UTM, WGS84
MERIS = lat/lon WGS84
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4. MERIS & CYCLOPES product definition
LAI = effective LAI
fAPAR = instantaneous fAPAR at 10h00
10/03/2005
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5. (2 spatial resolution: 1km – 8km) Up to now: 2 versions available
CYCLOPES PROJECT
Final objectives: provide LAI, fAPAR, fCover products derived from the fusion of AVHRR, VGT, POLDER data from 1997 to 2003
(2 spatial resolution: 1km – 8km)
Up to now: 2 versions available
Version 1 = VGT data derived from already existing processing chains. BRDF normalization using Roujean’s model, use relationships between Roujean’s coefficients and biophysical variables
Version 2 = algorithm based on neural nets calibrated on radiative transfer simulations using normalized TOC nadir reflectances
(for LAI: + fAPAR as input)
10/03/2005
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6. MERIS PRODUCT DESCRIPTION
Same philosophy (neural nets calibrated on radiative transfer simulations) except that
Inputs are Top of Atmosphere reflectances + pressure + view & satellite angles
No normalization: one LAI, fAPAR, fCover estimated at each date
Up to now, no cloud filtering is applied to the data. Application of a manual filtering + smoothing using gaussian filtering
10/03/2005
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7. MODIS Product description
LAI (sinusoidal projection) = collection 4 downloaded from EOS data gateway
fAPAR (sinusoidal projection) = The fAPAR MODIS standard product (collection 4) re-processed by BU
Relationship used for
Intercomparison with
MERIS
Use of the MODIS re-projection tool (nearest neighbor resampling because of flags) to provide the products in :
UTM/WGS84 (comparison with CYCLOPES)
Plate Carrée (Lat/lon WGS84) (comparison with MERIS)
10/03/2005
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8. The used sites VALERI sites in 2003:
Additional sites in 2003 AERONET+ VALERI (other years)
Turco, Bolivia
Barrax, Spain
Fundulea, Romania
Haouz, Morocco
Hirsikangas,Finland
Concepcion, Chile
Larose, Canada
AERONET: Banizoumbou, Bordeaux, Jabiru, Ouagadougou, Moldova, Fontainebleau
VALERI : - Grasslands: Laprida, ZhangBei, Larzac
- Shrublands: Gourma
- Croplands :Avignon_Alpilles, Sud-Ouest, Romilly, Gilching
- Forests :Counami, SierraCincua,AekLoba, Puechabon
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9. LAI-fAPAR relationships
- MGVI-LAI bad relationship
Bad results for CYCLOPES V1 for low canopies
Low scattering for CYCLOPES V2
-LAI higher for MODIS than other products
10/03/2005
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10. LAI,fAPAR cumulated distribution
Good consistency for fAPAR
Differences for low LAI & high LAIs
10/03/2005
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11. Comparison between products
Comparison with CYCLOPES products (interpolation of MODIS data at CYCLOPES dates) – UTM/WGS84 projection. Europe & Africa sites
Comparison with MERIS products (interpolation at MERIS dates) – lat/lon on WGS84. All sites
fAPAR: Good consistency between CYCLOPES V2/MODIS, MODIS/MERIS
LAI : more scattering. Higher LAI for CYC ENF, higher LAI for MOD DBF
HIGH values for MOD crops
10/03/2005
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12. Comparison with VALERI maps
CYC_V1
CYC_V2
fAPAR: Maybe problems with CAN-EYE when understorey
LAI : MERIS underestimates ENF although MODIS overestimates
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13. Temporal evolution for some VALERI sites
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20. Conclusions Encouraging results, especially for fAPAR
(computation of fAPAR in VALERI when understorey?)
More inter-comparison (BELMANIP) & validation (temporal monitoring of validation sites) are required to better understand the weaknesses of the different algorithms
10/03/2005
NOV-3300-SL-2858