The Global TanDEM-X High-Resolution Coastline Product

Kurzfassung

The coastline is commonly understood as the object that separates the terrestrial from the marine environment. As such, it is an important element in a broad range of GIS applications, where it can be used to mask out data. Spatial planning in the coastal, littoral and marine area as well as hazard modelling of tsunamis and storm surges are among the common tasks. In particular, a global coastline is required within the projects TanDEM-X and HydroSHEDS v.2. To support these functions, the Global TanDEM-X High-Resolution Coastline Product, short TanDEM-X coastline, has been developed. The TanDEM-X coastline is a vector dataset with global coverage at a resolution of 12 m. It is derived automatically from the TanDEM-X dataset and complemented with manual checking to fulfill requirements defined from a hydrological perspective. Next to the TanDEM-X Digital Elevation Model (DEM), the coastline is delineated from the associated amplitude layer (AMP) and height error map (HEM). The set of these layers allows to identify open water due to the backscatter and coherence characteristics of the radar signal over open water. To support the positioning of the TanDEM-X coastline, open water is detected in the neighbourhood of a reference coastline, which is derived from the water quality layer of the Copernicus DEM. As a consequence, the TanDEM-X coastline will remain within a specific margin around the reference coastline. While this works well to define the ocean-land-boundary, it can create inconsistencies at the divide between ocean and inland waters, i.e. estuaries, river mouths, lagoons, and similar objects, because ocean and inland waters cannot be differentiated purely from radar satellite data. To ensure that the requirements of hydrological applications and in particular HydroSHEDS v.2 are met, the coastline is manually positioned in selected areas taking different existing coastline products into consideration. Nonetheless, it has to be acknowledged that the coast is a transition zone between the terrestrial and marine sphere, whereas the coastline is an artificial structure. As such, the coastline position can only be defined alongside a set of parameters. The TanDEM-X coastline is a set of closed polygons representing mainland and islands without any holes that can be converted into line features. The overall quality of the coastline corresponds to that of the TanDEM-X dataset. Accordingly, the spatial resolution of 12 m is maintained in the coastal product. The high overall coverage of the TanDEM-X data with more than 99.98% is mirrored in the coastline in the way that the coast is also well covered on a global scale. The TanDEM-X coastline is a static product. On a temporal scale, the time stamp corresponds to the acquisition period of the TanDEM-X mission from 2010 to 2015.