Validation and Inter-Comparison of Spaceborne Derived Global and Continental Land Cover Products for the Mediterranean Region: The Case of Thessaly

Space agencies, international and national organisations and institutions recognize the importance of regularly updated and homogenized land cover information, in the context of both nomenclature and spatial resolution. Moreover, ensuring credibility to the users through validated products with transparent procedures is similarly of great importance. To this end, this study contributes with a systematic accuracy performance evaluation of continental and global land cover layers. Confidence levels during validation and a weighted accuracy assessment were designed and applied. Google Earth imagery were employed to assess the accuracy of three land cover products for the years 2010 and 2012. Results indicate high weighted overall accuracy rates of 89, 90, and 86% for CORINE Land Cover 2012, GIO High Resolution Layers, and Globeland30 datasets, respectively. Moreover, their inter-comparison highlights notable differences especially for classes Artificial Surfaces and Water. The deviation of specific classes from the general producer's and user's accuracy trends were identified. It is concluded that the different aspects of the employed land cover products can be highlighted more transparently and objectively by integrating confidence levels during the reference data annotation, by employing a stratified sampling based on the several Corine Level-3 subclasses and by applying a weighted overall accuracy procedure.