We show that high-resolution space-borne synthetic aperture radar (SAR) imagery with pixel sizes smaller than 1 m2 can be used to complement archaeological surveys on intertidal flats. After major ...storm surges in the 14th and 17th centuries (“Grote Mandrenke”), vast areas on the German North Sea coast were lost to the sea. Areas of settlements and historical farmland were buried under sediments for centuries, but when the surface layer is driven away under the action of wind, currents, and waves, they appear again on the Wadden Sea surface. However, 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 remains of farmhouse foundations and of former systems of ditches, dating back to the times before the “Grote Mandrenke”. In particular, the very high-resolution acquisition (“staring spotlight”) mode of the TerraSAR/TanDEM-X satellites allows detecting various kinds of remains of historical land use at high precision. Moreover, SARs working at lower microwave frequencies (e.g., that on Radarsat-2) may complement archaeological surveys of historical cultural traces, some of which have been unknown so far.
We developed an extension of a previously proposed classification scheme that is based upon Freeman–Durden and Cloude–Pottier decompositions of polarimetric Synthetic Aperture Radar (SAR) data, along ...with a Double-Bounce Eigenvalue Relative Difference (DERD) parameter, and a Random Forest (RF) classifier. The extension was done, firstly, by using dual-copolarization SAR data acquired at shorter wavelengths (C- and X-band, in addition to the previously used L-band) and, secondly, by adding indicators derived from the (polarimetric) Kennaugh elements. The performance of the newly developed classification scheme, herein abbreviated as FCDK-RF, was tested using SAR data of exposed intertidal flats. We demonstrate that the FCDK-RF scheme is capable of distinguishing between different sediment types, namely mud and sand, at high spatial accuracies. Moreover, the classification scheme shows good potential in the detection of bivalve beds on the exposed flats. Our results show that the developed FCDK-RF scheme can be applied for the mapping of sediments and habitats in the Wadden Sea on the German North Sea coast using multi-frequency and multi-polarization SAR from ALOS-2 (L-band), Radarsat-2 (C-band) and TerraSAR-X (X-band).
We demonstrate that Synthetic Apertur Radar (SAR) data have great potential to improve an existing monitoring system based on optical data for intertidal flats and to complement the classification of ...sediments, macrophytes, and mussels in the German Wadden Sea. Multi-satellite SAR data acquired at different radar bands (L, C, and X band, from ALOS PALSAR, from ERS SAR, Radarsat-2 and ENVISAT ASAR, and from TerraSAR-X, respectively) were used to investigate whether they can be jointly used for crude sediment classification on dry-fallen intertidal flats and for detecting benthic fauna such as blue mussel or oyster beds. In this respect, we show that both multi-satellite and multi-temporal analyses provide valuable input for the routine monitoring of exposed intertidal flats on the German North Sea coast, the latter already improving the identification of the spatial extent of mussel (oyster) beds. In addition, we demonstrate that high-resolution SAR is capable of detecting residuals of historical land use in areas that were lost to the sea during major storm surges in the 14th and 17th centuries.
The change of mapping methods for seagrass beds, here species of eelgrasses, from aerial surveys to automated classification of optical satellite data is described. Both methods are compared with ...respect to availability and suitability of their data. Differences in the detection capability of the methods are shown as well as results of the validation of the satellite image classification.
In North Friesia, where the largest area of eelgrass occurs in the Wadden Sea, eelgrass beds have been mapped regularly using aerial surveys since 1994. After a significant decline in the 1930s and 1960s, monitoring results show a steady increase in the size of the area covered by eelgrass beds up to 2017.
Since 2006, the aerial surveys have been complemented by ground surveys, which, however, only cover one sixth of the area of the Schleswig-Holstein Wadden Sea each year. Results show that size estimates of individual beds can vary significantly between aerial and ground surveys.
In recent years, satellite-borne remote sensing technology and subsequent analysis methods have reached a level of quality, which makes them an alternative and cost-efficient method for mapping eelgrass. The technology has advantages such as the coverage of large areas at single points in time, repeatable and transferable image analysis methods, and high spatial resolution of the satellite images, as well as frequent repetition of acquisition of data. This provides standardised results, which allow direct comparisons over time and between areas.
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•Detection of seagrass/ealgrass from space.•Comparison of seagrass stock detected by different sensor technology and ground truth.
Neobiotic species can have profound impacts on food webs and entire ecosystems. The American razor clam Ensis leei was introduced into the Wadden Sea by vessels in the late 1970s and has since spread ...widely. It has been suggested that Ensis does not interact strongly with other benthic species. The abundance and biomass of E. leei were recorded in 2393 samples in the north-eastern Wadden Sea and 800 samples in the south-eastern Wadden Sea over a total period of 9 years. Using an interdisciplinary approach, we developed a habitat prediction model using sedimentological and hydrodynamic predictors to help understand the shape of the ecological niche occupied by Ensis in the Wadden Sea. Our model showed that Ensis preferred areas with moderately high bed shear stress and prolonged or constant water coverage. Ensis preferred coarse sediments in the northern sub-area but coarse and muddy sediments in the southern sub-area and was negatively affected by the sand mason worm Lanice conchilega in the northern sub-area. Predictions of the spatial distribution of Ensis using the northern and southern datasets revealed major differences in predicted hot-spots throughout the entire study site. This study thus highlights the need to collect a sufficiently large dataset from different sub-areas of the Wadden Sea to allow valid conclusions to be drawn regarding the spatial distribution of Ensis. The negative effects of L. conchilega on Ensis abundance and biomass as well as the occurrence of Ensis in muddy sediments in the south suggest that the ecological niche of this neobiotic species is likely to overlap partly with the native fauna of the Wadden Sea.
•Long-term data were used to determine ecological niche and predict habitat potential of Ensis leei.•Abundance and biomass of Ensis were related with sedimentologic and hydrodanamic predictors.•Ensis occurred both, in coarse sediments as well as in muddy environments.•Ensis abundance and biomass declined in areas with dense Lanice conchilega reefs.•The invasive Ensis is thought to overlap with the pristine benthic fauna particularly in muddy sediments.
The Wadden Sea along the North Sea coasts of Denmark, Germany, and the Netherlands is the largest unbroken system of intertidal sand and mud flats in the world. Its habitats are highly productive and ...harbour high standing stocks and densities of benthic species, well adapted to the demanding environmental conditions. Therefore, the Wadden Sea is one of the most important areas for migratory birds in the world and thus protected by national and international legislation, which amongst others requires extensive monitoring. Due to the inaccessibility of major areas of the Wadden Sea, a classification approach based on optical and radar remote sensing has been developed to support environmental monitoring programmes. In this study, the general classification framework as well as two specific monitoring cases, mussel beds and seagrass meadows, are presented. The classification of mussel beds profits highly from inclusion of radar data due to their rough surface and achieves agreements of up to 79 % with areal data from the regular monitoring programme. Classification of seagrass meadows reaches even higher agreements with monitoring data (up to 100 %) and furthermore captures seagrass densities as low as 10 %. The main classification results are information on area and location of individual habitats. These are needed to fulfil environmental legislation requirements. One of the major advantages of this approach is the large areal coverage with individual satellite images, allowing simultaneous assessment of both accessible and inaccessible areas and thus providing a more complete overall picture.
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.
After major storm surges in the 14 th and 17 th centuries, vast areas on the German North Sea coast were lost to the sea. However, remnants of former settlements and of historical landuse, which were ...buried by sediments for several centuries, can still be found in the German Wadden Sea, if the surface layer is driven away under the permanent action of wind, currents, and waves. We show that high-resolution SAR imagery with pixel sizes well below 1 m 2 can be used to complement archeological surveys and that TerraSAR/ TanDEM-X images clearly show remnants of farmhouse foundations and of former systems of ditches, dating back to the 14 th century and to the 16 th /17 th century. In particular, the new high-resolution TerraSAR-X acquisition mode (`staring spotlight') allows for the detection of various kinds of residuals of historical landuse, some of which have been unknown so far.
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