Validation of the GLC2000 products

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Validation of the GLC2000 products

• Philippe Mayaux

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GLC 2000 validation strategy

• Confidence-building method
• Systematic review of the regional products by
  experts and comparison with reference data
• Design-based method
• Quantitative accuracy assessment of the global
  product using a stratified random sampling of
  high-resolution sites (in agreement with the
  CEOS-IGOS recommendations)

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Objectives of the quality control

• to avoid macroscopic errors before the
  quantitative accuracy assessment
• Wrong labels limits
• Inter- and intra-continental inconsistencies
• Location of the errors (thematic or geographical)
  
• to improve the global acceptance of GLC2000
  products
• collaboration with local partners

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Confidence-building method

• Systematic descriptive protocol to document the
  verification per cell (proposed size 2 by 2
  degrees at the equator 50,000 km2)
• Use of ancillary data (maps, Landsat SPOT
  images, aerial photographs), expert opinion and
  intrinsic properties of the dataset (temporal
  profiles, colour composites)
• Archive the evaluation in a database

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The qualitative validation grid
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Qualitative check fields

• Name of the expert
• Type of reference material high-resolution
  image, quick-look, thematic map, aerial
  photograph, field photograph
• Spatial pattern from homogenous to heterogeneous
  (4 levels)
• Overall quality of the GLC product, very good,
  good, acceptable, unacceptable
• LC classes well-identified and LC classes poorly
  identified
• Nature of problem label, limit, missing class,
  other

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Status of the quality control

• Regions covered Eurasia, Asia, Scandinavia,
  Africa, Canada

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Derived analysis
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An example in Russia
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An exemple in Asia
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Design-based validation

• Objective To provide a statistical assessment of
  the accuracy by class and an overall accuracy of
  the global map.
• Constraints
• budget (data, interpretation)
• time
• spatial complexity
• seasonality

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Key issues for the validation

• Sampling issues (scheme, frame, size)
• Reference material (nature, interpretation)
• Accuracy statements (contigency matrix, fuzzy
  logic, double regression)
• Single pixels or pixel blocks?
• Upscaling of legends (mosaic classes)
• Spatial pattern (linear, massive, diffuse)
• Rare classes important for several users
• Universal dataset
• Detailed discussion during the CEOS workshop
  Validation of Global Land-Cover Products, 27-28
  March

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Land-cover class area
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Regions of interest
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Land cover area per region
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Random sampling equally distributed per region
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Stratified sampling per class
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Stratified sampling per class
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Stratified sampling per class
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Interpretation of reference material

• Reference material high spatial resolution
  interpretations
• CNES NASA / USGS / UNEP-GRID
• Existing sources of images
• Interpretation by local experts
• Very-well focused (better 1 or 2 good experts
  than a pool of less qualified experts)
• Contracts with GVM Unit when necessary (realised
  on-site)
• Visual interpretation
• Efficiency
• Accuracy
• LCCS-based interpretation of the high-resolution
  images

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