Validation of the GLC2000 products Philippe Mayaux

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)

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

Confidence-building method  Systematic descriptive protocol to document the verification per cell (proposed size = 2 by 2 degrees at the equator ~ 50,000 km 2 )  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

The qualitative validation grid

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

Status of the quality control Regions covered: Eurasia, Asia, Scandinavia, Africa, Canada

Derived analysis

An example in Russia

An exemple in Asia

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

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”, March

Land-cover class area

Regions of interest

Land cover area per region

Random sampling equally distributed per region

Stratified sampling per class

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