30 m-scale Annual Global Normalized Difference Urban Index Datasets from 2000 to 2021

Urban areas play a very important role in global climate change. There is an increasing interest in comprehending global urban areas with adequate geographic details for global climate change mitigation. Accurate and frequent urban area information is fundamental to comprehending urbanization processes and land use/cover change, as well as the impact of global climate and environmental change. Defense Meteorological Satellite Program/Operational Line Scan System (DMSP/OLS) night-light (NTL) imagery contributes powerfully to the spatial characterization of global cities, however, its application potential is seriously limited by its coarse resolution. In this paper, we generate annual Normalized Difference Urban Index (NDUI) to characterize global urban areas at a 30 m-resolution from 2000 to 2021 by combining Landsat-5,7,8 Normalized Difference Vegetation Index (NDVI) composites and DMSP/OLS NTL images on the Google Earth Engine (GEE) platform. With the capability to delineate urban boundaries and, at the same time, to present sufficient spatial details within urban areas, the NDUI datasets have the potential for urbanization studies at regional and global scales.