Validation of CYCLOPES, MODIS & MERIS PRODUCTS M. Weiss, F. Baret, K. Pavageau, P. Bicheron, M. Huc, D. Béal, W.Wang 10/03/2005 NOV-3300-SL-2858

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 » 10/03/2005 NOV-3300-SL-2858

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 10/03/2005 NOV-3300-SL-2858

MERIS & CYCLOPES product definition LAI = effective LAI fAPAR = instantaneous fAPAR at 10h00 10/03/2005 NOV-3300-SL-2858

(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 NOV-3300-SL-2858

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 NOV-3300-SL-2858

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 NOV-3300-SL-2858

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 10/03/2005 NOV-3300-SL-2858

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 NOV-3300-SL-2858

LAI,fAPAR cumulated distribution Good consistency for fAPAR Differences for low LAI & high LAIs 10/03/2005 NOV-3300-SL-2858

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 NOV-3300-SL-2858

Comparison with VALERI maps CYC_V1 CYC_V2 fAPAR: Maybe problems with CAN-EYE when understorey LAI : MERIS underestimates ENF although MODIS overestimates 10/03/2005 NOV-3300-SL-2858

Temporal evolution for some VALERI sites 10/03/2005 NOV-3300-SL-2858

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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