## 3 Results
### Mud Field  
The large mud field close to the watershed of the tidal flats beneath the island of Norderney extends over ca. 1.8 km along the Riffgat channel (see Figure 9) with a width of 300-400 m. On the wavy to humpy sediment surface, water puddles formed between the muddy humps resulting in a characteristic pattern (see Figure 9e), leading to a relatively high backscatter in the TerraSAR-X data. In addition, the mud field is traversed by a dense network of highly branched gully structures which drain the water from the adjacent depression in the south of the mud field to the channel in the north. These properties lead to a specific reproduction of the mud field in the TerraSAR-X images characterized by a high backscatter and the recognizable texture of the many gully structures (see Figure 9b). The contrast with the Riffgat channel and the water covering the area of the depression also facilitate to determine the contours of this mud field. In situ the southern edge of the mud field is clearly marked by the finely branched gullies originating from the water-covered depression. Here, the surface of the muddy deposits stands out from the more solid, smoother sediment surface of the depressed area (see Figure 9c,d). Therefore, GPS measurements of the mud field's edge carried out in summer 2011 (27/07/2011) show very good agreement with the contours reproduced by the TerraSAR-X acquisition recorded within a short time frame (16/07/2011). In Figure 9b, the yellow line represents the GPS measurement. Figure 8: Temporary linear surface structures in the tidal area south of Wangerooge: (**a**) Tidal flats between the island of Wangerooge and the mainland coast, rectangle marks image Section b (SL of 19/05/2012, asc. ); (**b**) linear surface structures within and in the surroundings of a cockle field (_C. edule_), point marks position of photographer; (**c**) photography of surface structures (02/06/2012). Seasonal Aspects  
In situ studies show variations in the surface form of the mud field. Extent and height of the muddy humps vary as well as their shape, which can be smooth and wavy or in contrast have steep erosive edges. These variations may occur locally, e.g., the silt surface always tends to be smoother on the edge of the mud field towards the depression. Overall, however, the field surveys showed that the mud field surface was more pronounced during the calmer season of the year (usually the summer) than after the stormy time of winter. When GPS-measuring the mud field's edge in summer 2011 (27/07/2011), the mud deposits clearly stood out from the depressed area covered with water. Thus, the boundary of the mud field was obvious and also well defined by the waterline (see Figure 9b,c). In the following January (17/01/2012), after two storms had passed through in the first days of the month (03-06/01/2012), a much more gradual transition was observed from the depression to the mud field. While the gully deltas where still in place, the smooth, slightly wavy surface of the silt accumulation began to emerge only gradually from the lower area, just beyond the ends of the gully deltas. In fact, regarding the mud field over several years (2011-2015) in the TerraSAR-X data, seasonal changes are observed. During summer, the mud field surface is displayed in full width with high backscatter, in winter, however, the area of high backscattering retreats towards the Riffgat channel. The internal gully structures, on the other hand, remain visible throughout the year, across the entire width from channel to depression. This can be seen in Figure 10a-d showing the reproduction of the mud field in TerraSAR-X acquisitions from summer 2013, the following winter (02/2014) and the next summer (06/14) and winter (12/2014). Figure 9: Large mud field in the tidal area of Nordermey: (**a**) location of the mud field close to the watershed, marked by oval line (HRS of 02/06/2011, asc. ); (**b**) GPS measurement of mud field’s edge taken on 27/07/2011 (yellow line) compared to TerraSAR-X HRS of 16/07/2011, asc.