Seminar Ozean, Eis, Atmosphäre

Termin: 06.11.2001

Referent/in: Jan Dannenberg, iup-Bremen (Physikalische Satellitenbildanalyse)

Titel: Wadden Sea

The tidal flats of the Wadden Sea along the coast of northwest Germany are highly dynamic areas whose topography changes on timescales from a few hours (storm events) up to several months (sediment ablations and disposal).

Conventionally generated maps based on echo sounding and geodetic leveling techniques often do not represent the actual situation because it takes several years to map the complete Wadden Sea. With the help of remote sensing data, especially ERS-SAR images, it is possible to achieve a more frequent updating of the topographic maps of tidal areas between high and low water level using the 'waterline method'. For this purpose waterlines in ERS-SAR images acquired at different tidal levels are extracted using a wavelet based edge detection algorithm. After geocoding the SAR images, each point of the extracted waterlines is assigned to a water level provided by a water level model to represent the height of the sea bottom. The operational model of the German Maritime and Hydrographic Agency (BSH) calculates currents and water levels based on forecasts of wind and air pressure above the North Sea. The heights of the points along each waterline form a random grid of topographic points with a wide spacing when the gradient of the sea bottom is flat and a narrow spacing when the gradient is steep. A digital elevation model can be derived from this irregular grid by triangulation and interpolation.