A fuzzy-based method for the regional validation of global maps: the case of MODIS-derived phenological classes in a mega-diverse zone

Regional validation studies of global land cover products are usually based on medium-resolution imagery and auxiliary high-resolution information. Because of the heterogeneity of landscapes at 500-1000 m resolution and the characteristics of the reference sites/data, the accuracy of the results may depend on the methodology used. This work proposes an integration scheme for the regional validation of global products. The assessment produces an accuracy index with possibility margins, representing various levels of positional, thematic and temporal tolerance. The methodology is used to evaluate MOD12Q1 on 1 million km2 of the land cover in Mexico, with emphasis on the diversity of forest types/phenologies. The area of higher confusion is reported in deciduous tropical dry forests, which tend to be classified as evergreen forests, and in oak forests, which tend to be classified as grassland. The index could be used as a tool for the consistent comparison between validation results among regions.