Abstract
Abstract. We show that high-resolution space-borne Synthetic Aperture Radar (SAR) imagery with pixel sizes well below 1 m2 can be used to complement archaeological surveys in areas that are difficult to access. After major storm surges in the 14th and 17th centuries, vast areas on the German North Sea coast were lost to the sea. Areas of former settlements and historical land use were buried under sediments for centuries, but when the surface layer is driven away under the permanent action of wind, currents, and waves, they appear again on the Wadden Sea surface. However, the frequent flooding and erosion of the intertidal flats make any archaeological monitoring a difficult task, so that remote sensing techniques appear to be an efficient and cost-effective instrument for any archaeological surveillance of that area. Space-borne SAR images clearly show remnants of farmhouse foundations and of former systems of ditches, dating back to the 14th and to the 16th/17th centuries. In particular, the very high-resolution acquisition (staring spotlight) mode of the German TerraSAR/ TanDEM-X satellites allows for the detection of various kinds of residuals of historical land use with high precision. In addition, we also investigate the capability of SARs working at lower microwave frequencies (on Radarsat-2) to complement our archaeological survey of historical cultural traces, some of which have been unknown so far.
Highlights
In Medieval times, the German North Sea coastline was very different from how it is today: the North Frisian islands did not yet exist, but were still what was called the ‘Uthlande’ and what was part of, or connected with, the mainland (Behre, 2009)
The area of interest lies in the center of the North Frisian Wadden Sea, i.e. in an area, which was most affected by the major storm surges in the 14th and 17th centuries
A total of 26 TerraSAR-X/TanDEM-X images acquired in highresolution spotlight mode between 2008 and 2014 form the basis for our systematic analyses of Synthetic Aperture Radar (SAR) signatures of historical land use
Summary
In Medieval times, the German North Sea coastline was very different from how it is today: the North Frisian islands did not yet exist, but were still what was called the ‘Uthlande’ (outer lands) and what was part of, or connected with, the mainland (Behre, 2009). As a result of that storm surge, which is known in history as the Saint Marcellus’ Flood or ‘Grote Mandrenke’ (‘great drowning of men’), huge land areas were lost to the sea, and they haven’t been diked ever since (compare the upper and middle panels of Figure 1) Thereafter, it took a long time until new dikes were built to protect the remaining marsh land. Under the permanent action of the tidal forces the muddy and sandy marine sediments are partly driven away, and traces of former peat digging, drainage systems, and settlements appear again on the surface (Bantelmann, 1967) Since those areas are difficult to reach, and to observe from ground, airborne sensors have proven to be advantageous for a systematic observation of the residuals of those historic places (Gade and Kohlus, 2011, 2015). Their use, is costintensive, which makes high-resolution space-borne sensors an alternative source of data that can be used by archaeologists for their frequent surveillance of the area (Gade et al, 2014; Gade and Kohlus, 2016)
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