###### Abstract  
Spatial distribution and dynamics of intertidal habitats are integral elements of the Wadden Sea ecosystem, essential for the preservation of ecosystem functions and interlocked with geomorphological processes. Protection and monitoring of the Wadden Sea is mandatory and remote sensing is required to survey the extensive, often inaccessible tidal area. Mainly airborne techniques are carried out for decades. High-resolution satellite-borne sensors now enable new possibilities with satellite synthetic aperture radar (SAR) offering high availability of acquisitions during low water time due to independence from daylight and cloud cover. More than 100 TerraSAR-X images from 2009 to 2016 were used to examine the reproduction of intertidal habitats and macrostructures from the flats south of the island of Nordermey and comparative areas in the Lower Saxony Wadden Sea. As a non-specific, generic approach to distinguish various and variable surface types continuously influenced by tidal dynamics, visual analysis was chosen which was supported by extensive in situ data. This technically unsophisticated access enabled us to identify mussel beds, fields of shell-detritus, gully structures, mud fields, and bedforms, the latter detected in the upper flats of every East Frisian island. Based on the high frequency of TerraSAR-X recordings for the Nordermey area, a bedform shift was observed in a time-series from 2009 to 2015. For the same period, the development of a mud field with an adjoining depression was traced. Beside seasonal variations of the mud field, the formation of a mussel bed settling in the depression was imaged over the years. This study exemplifies the relevance of TerraSAR-X imagery for Wadden Sea remote sensing. Further development of classification methods for current SAR data together with open access availability should contribute to large-scale surveys of intertidal surface structures of geomorphic or biogenic origin and improve monitoring and long-term ecological research in the Wadden Sea and related tidal areas. synthetic aperture radar; TerraSAR-X; habitat mapping; monitoring; remote sensing; Wadden Sea; mussel beds; intertidal bedforms; tidal gullies 2018 10.3390/rs10071085 10.  
the open North Sea. The Wadden Sea is one of the last large-scale and near-natural ecosystems in Central Europe, whose ecological functions are supraregional and of far-reaching importance, e.g., as an indispensable stepping stone for birds migrating on the East Atlantic Flyway. In addition, it also plays an important role in coastal protection. The Wadden Sea is protected by a high national as well as international conservation status and it is listed as UNESCO world heritage site. Regular monitoring of the area is mandatory but complex and expensive because of the large area of rough terrain which is accessible only in tight timeframes due to the changing tides. Therefore, remote sensing techniques are required and aerial mapping and photography (e.g., mussel beds, seagrass meadows, salt marsh vegetation) as well as airborne lidar (light detection and ranging) provide the high resolution needed to determine surface structures of the tidal flats or salt marsh vegetation types. Today they are applied in operational monitoring programs of the Wadden Sea. Aerial photographs have been used in the Lower Saxony Wadden Sea since the 1990s for the monitoring of mussel beds [1; 2; 3] and for biotope mapping of the salt marshes [4; 5; 6]. Aerial photography and lidar are also used by the responsible authorities for coastal protection (NLWKN, unpublished data). A possible support of the seagrass mappings by aerial photographs was examined by [PERSON]. [7]. Advances in synthetic aperture radar (SAR) technology have enabled a high level of spatial resolution also for satellite-borne sensors implemented by a new class of high-resolution SAR satellites.