Monitoring of global urbanization-time series analyses for mega cities based on optical and SAR data

Mega cities and their development are a synonym for the steady and dynamic trend of global urbanization. The number of these extreme metropolises exploded from three mega cities in 1975 (Mexico City, New York, Tokyo) to actually 27 and it is expected that more than 100 new ones will emerge within the next three decades. However, particularly in developing countries the spatiotemporal characteristics of mega cities development are still not well known. Therefore, this study introduces the concept and results of a global monitoring of the spatiotemporal mega cities development based on Earth Observation (EO) data. We applied straightforward, semi-automated object-oriented and pixel-based image classification algorithms to high resolution (HR) optical (Landsat) and very high resolution (VHR) SAR (TerraSAR-X) imagery covering a time span of 40 years in an interval of 10 years. By mapping the extent of the urban area for each single decade, we could subsequently apply post-classification change detection methods to visualize the dimension, patterns and dynamics of urban sprawl for the current 27 mega cities. The results of this study demonstrate the capabilities and benefits of satellite-based EO to support the collection of data on global urbanization trends and patterns. The analyses also showed the high potential of VHR SAR data for a more detailed characterization of settlement patterns and urban morphology.