Intercomparison GLOBCARBON CYCLOPES

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Integrated GMES Project on Landcover and
Vegetation
INTER-COMPARISON GLOBCARBON / CYCLOPES LAI
FIRST RESULTS
geoland
Co-funded by the European Commission within the
GMES initiative in FP-6
Roselyne Lacaze Marie Weiss Medias-France
Noveltis 17.01.2006
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Introduction

• What is CYCLOPES?
• LAI products used for intercomparison
• Validation
• spatial and temporal variability
• comparison with MODIS LAI
• comparison with in-situ measurements
• Conclusion

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What is CYCLOPES ?

• FP5/EU project coordinated by Inra with CNRM,
  Medias-France, Noveltis Cnes as partners
• Objectif developing and validating biophysical
  variables (albedo, LAI, FAPAR, fCover) from VGT,
  AVHRR, Polder, Meris.
• Products mono multi-sensor global parameters
  from 1 to 8 km resolution over 1997-2003 period
  with a 10-day temporal resolution.
• Applications
• detection and categorisation of land use change
  (UCL)
• exploitation within global carbon models
  (MPI-BGC, MPI-MET)

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LAI products used for intercomparison
Algorithms

• CYCLOPES
• bi-directional normalisation
• SAIL PROSPECT empirical soil description
• Neural network
• nadir normalized reflectance B2, B3, MIR
• sun zenith angle 1000 local time
• daily fAPAR
• -gt LAIe

• GLOBCARBON
• 2 algorithms to retrieve LAIe
• LAIe f(RSR, fBRDF) for forest classes
• LAIe f(SR, fBRDF) for other vegetation
• fBRDF from modified Roujean model
• Iterative process
• Empirical clumping index
• -gt True LAI

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LAI products used for intercomparison
Technical properties

• GLOBCARBON
• sensor VGT ATSR
• spatial resolution 10 km
• temporal resolution monthly
• spatial coverage global
• temporal coverage 2002
• grid Plate Carree
• no data 0 (water), 255 (bad data)
• 18,7 of valid pixel (grid) no gaps due to
  clouds

• CYCLOPES
• sensor VGT
• spatial resolution 8 km
• temporal resolution 10-day
• spatial coverage global
• temporal coverage 2002
• grid Plate Carree
• no data 255 (water cloud)
• from 11,4 to 19,3 of valid pixel (grid)

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Validation - 1
LAI distribution at global scale

• GLOBCARBON vs CYCLOPES
• more small ( 0.1,1 ), and large values ( gt 6 )
• deficit of intermediate values ( 2, 4 ) and
  none LAI0
• discontinuous histogram

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Validation - 2
Spatial variability transect over Africa (25E)

• GLOBCARBON vs CYCLOPES
• stronger gradients on both sides of forest
• stronger seasonal variations over transitional
  vegetation
• unrealistic seasonal variations over forest

LAI GLOBCARBON
LAI CYCLOPES
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Validation - 3
Spatial variability transect over Europe (30E)

• GLOBCARBON
• lower LAI
• strong seasonal variations

• CYCLOPES
• stable over taïga
• unrealistic high LAI in winter

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Validation - 4
Difference (GLOBCARBON CYCLOPES) at global scale
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Validation - 5
Difference (GLOBCARBON CYCLOPES) at local scale
GLOBCARBON CYCLOPES
DIFFERENCE
June 2002
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Validation - 6
Comparison with MODIS LAI

• MODIS LAI
• Radiative transfer model (LUT) back up
  (empirical relationship with NDVI)
• -gt True LAI

• MODIS ASCII subset
• spatial resolution 1km
• spatial coverage 7 x 7 km²
• temporal resolution 8-day
• temporal coverage 2002

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Validation - 7
Scatterplot over FLUXNET sites
02-2002 05-2002
08-2002 11-2002
GLOBCARBON closer to CYCLOPES than to
MODIS CYCLOPES closer to MODIS than GLOBCARBON
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Validation - 8
Comparison with in-situ measurements

• VALERI, BIGFOOT
• networks of instrumented sites for satellite
  validation
• in-situ data upscaled with high resolution
  images
• optical measurements -gt LAIe

• BIGFOOT
• 1 Evergreen Needleleaf Forest
• 1 Evergreen Broadleaf Forest
• 2 Deciduous Broadleaf Forest
• 2 Grassland
• 1 Bare Soil

• VALERI
• 1 Evergreen Needleleaf Forest
• 2 Evergreen Broadleaf Forest
• 3 Crops
• 1 Grassland
• 1 Bare Soil

OTHER 2 Evergreen Needleleaf Forest
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Validation - 9
Seasonal profiles over some instrumented sites
Ever. Broad. forest, Brazil
Crops, France
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Validation - 10
Scatterplot with in-situ measurements
rmse CYCLOPES 1.17 GLOBCARBON 1.52
ECOCLIMAP 1.52 MODIS 2.33
Filled symbol 2002 No filled symbol not 2002
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Conclusion
CYCLOPES LAI represents better the vegetation
variations than the GLOBARBON LAI.
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Contact
Roselyne Lacaze lacaze_at_medias.cnes.fr