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Remotely sensing the German Wadden Sea—a new approach to address national and international environmental legislation

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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.

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We thank H. Büttger and H. Farke as well as all colleagues and volunteers who assisted with the data collection during field campaigns. F. Leverenz and F. Werner helped in the processing of TSX data. Furthermore, we like to thank M. Nyenhuis and colleagues from the German Aerospace Center (DLR) for constructive support during the SAMOWatt project. We also thank the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research on Sylt, BioConsult SH in Husum, and Syltair on Sylt, as well the National Park Authorities in Lower Saxony and Schleswig-Holstein for providing monitoring data and/or logistical support during data collection. TerraSAR-X data were provided by DLR under contract OCE0994. Data from Landsat-7 and Landsat-8, RapidEye, and SPOT-4 were obtained from the USGS, RESA, and the ESA Third Party Mission.

Funding was received from the German Ministry of Economy (BMWi) for the projects DeMarine SAMOWatt (contract numbers 50EE1112, 50EE1115, 50EE1117) and DeMarine-Environment TP4 (contract numbers 50EE0830, 50EE0816, 50EE0817).

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Correspondence to Martin Gade.

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Müller, G., Stelzer, K., Smollich, S. et al. Remotely sensing the German Wadden Sea—a new approach to address national and international environmental legislation. Environ Monit Assess 188, 595 (2016).

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