The DISCover validation image interpretation process

Thematic validation of the International Geosphere Biosphere Data and Infor mation System (IGBP-DIS) Global 1-Kilometer Land-Cover Data Set (DISCover) was performed utilizing a "state-of-the-practice" technique by a team of Ex pert Image Interpreters (EII) examining subscenes extracted from 379 digita l Landsat TM (Thematic Mapper) and SPOT images. The 15 validated IGBP land-cover classes (Snow/Ice and Wafer were not asses sed) were not equally interpretable on the TM and SPOT imagery Interpreter confidence was highest for Evergreen Broadleaf Forests and Urban/Built-up D ISCover classes while Grasslands and Permanent Wetlands were interpreted wi th relatively less confidence. Analysis of image interpretation in each of the 13 validation regions indicates that confidence in interpretations for North America/Canada (Region 1) and Central Asia/Japan (Region 11) are lowe r than average. Confidence in interpretations is significantly higher than average for North America/US (Region 2), Northern and Southern South Americ a (Regions 4 and 5), and Southest Asia and China (Region 12). In this study , variations in interpretation confidence are also noted between regions or based upon the geographic location of samples. This exercise demonstrates that Landsat TM and SPOT imagery can be efficien tly used to validate high-resolution global land-cover products. The result s suggest that the utility of and confidence that may be placed in this tec hnique depends upon the land-cover classification scheme used and the quali ty of digital and ancillary data available to aid interpreters. Another imp ortant factor is the relative confidence of the interpreters to verify the land cover within their respective areas of the globe.