High-Resolution Global Monitoring of Urban Settlements

Since the beginning of the 21st century, more than half of the global human population is living in urban environments and the dynamic trend of urbanization is expected to grow incredibly fast, with the number of urban dwellers currently increasing by about 180.000 people every day. In this framework, an effective monitoring of urban sprawl represents a key issue to analyse and understand the complexity, cross-linking and increasing dynamics of urban environments in order to ensure a sustainable development of urban and peri-urban areas. To this purpose, in the last decades satellite Earth observation (EO) has proved to be a promising tool in combination with widely automated methods of data processing and image analysis for providing up-to date geo-information on urban settlements at global scale; nevertheless, the geometric resolution of the current EO-based geo-information products is limited to 300-500 m, thus often resulting in poor accuracy to support decision makers and urban planners. TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurement) is a German radar satellite mission aiming at the provision of a global digital elevation model (DEM) at 12 m spatial resolution. Besides this primary goal, the global coverage with very high resolution (VHR) TerraSAR-X (TSX) and TanDEM-X (TDX) imagery collected in 2011 and 2012 can be used to characterize settlement patterns worldwide in a so far unique spatial detail. Accordingly, the German Remote Sensing Data Center (DFD) of the German Aerospace Center (DLR) has implemented a fully-automated processing system that detects and extracts built-up areas from the global TSX/TDX imagery acquired in the context of the TDM. The output of this approach is a global binary settlement mask that outlines urban and non-urban areas at the unprecedented spatial resolution of ~0.4 arc sec (i.e., ~12 m). The intended, world-wide data set is called Global Urban Footprint (GUF) and a public domain version of it will be made available at ~3 arcsec (i.e., ~50-75m) spatial resolution. With its global coverage and the enormous spatial detail, this initiative represents a promising contribution to global analyses of urban and peri-urban areas.