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- THE WADDEN SEA IN ONE PERSPECTIVE -

MOSAICING SATELLITE IMAGES

  In contract with the Common Wadden Sea Secretariat (CWSS) a satellite mosaic was produced showing the whole Wadden Sea ranging from Denmark over Germany to The Netherlands. The aim was to display the tidal flats of the Wadden Sea at once. This is not a realistic view, because the tidal wave moves from north to south radially along the coast and covers always parts of the intertidal flats. This mosaic enables the one-off chance to look at the total area of the trilateral Wadden Sea. But not only this view is fascinating. Beside this, the sediment transport into the North Sea can be detected very well. The suspended matter is transported from the rivers and the tidal flats along the coast and into the North Sea. The northern part of the mosaic, west of Blåvands Huk and Fanø a huge algal bloom can be seen. Or regarding the embankment of the Lake IJssel, different water bodies show different structure and colour depending on different water constituents.

  Such an image can only be produced by combining different satellite images from different acquisition dates. The satellite system was the Landsat 7 ETM, which has a spatial resolution of 30 x 30 m. This means that each pixel of the image represents an area of 30 x 30 m at the surface. Landsat detects the surface of the earth with 7 bands, sensible for different wavelength ranges of the spectrum of light. In order to produce an image with realistic colours, the 3 bands detecting the visible light (red - green - blue) are combined to an RGB image. The satellite images had to be chosen in that way that the cloud conditions and tidal stage allow the view on the land, tidal flats and the North Sea. This reduced the potential images very much, so that the images date from 3 different years and from different seasons. This causes phenological differences and therefore differences in the colours of the images. The 5 images which were acquired in April 2003, Mai 2000 and 2001 and Juli 2002 had to be adjusted geographically and colour wise. The spatial extension of the Mosaic come to ca. 340 km in from North to South and ca. 460 km from West to East.

 
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Kerstin Stelzer
Geographer
kerstin.stelzer@brockmann-consult.de
Telefon: +49(0)4152-889-307
 
Environmental Informatics • Geo-Information products