Flotsam in the North Sea
Measurements and computer models help us determine where flotsam drifts in the North Sea.
Container overboard! Where does oil drift after a maritime accident? In which direction do damaging algae float? We require methods in such situations to ascertain where this “flotsam” ends up after a particular period of time.
At the Institute of Coastal Research in the Helmholtz-Zentrum Geesthacht (HZG), current field predictions are generated for the German North Sea. Using these predictions, such scenarios can be calculated to help rescue operations utilize their resources most effectively. Measurements are combined with computer models in order to generate projections that are as realistic as possible.
In the framework of COSYNA (Coastal Observing System for Northern and Arctic Seas), measurements of HF-radar stations on the German North Sea coast (on Sylt, Wangerooge and in Büsum) are continuously recorded and then transferred to the data center at the Institute of Coastal Research of the HZG in Geesthacht. The surface currents of the sea are calculated—every twenty minutes and with a spatial resolution of two kilometers—from the backscatter of the sea surface. Measurements, however, always have limitations: they record only the present conditions, the radar instruments have a limited range of just over one hundred kilometers and technical problems or maintenance power outages can occur now and again. The measurement data, therefore, are supplemented by computer modeling of the currents in the German Bight in order to fill gaps and to calculate and predict the current fields.
The measurements are processed (“assimilated”) in three-dimensional ocean circulation models based on empirical values for precision of the measurements as well as of the models. A surface current field is then calculated, which reflects the actual condition of the North Sea. In order to make statements about the future drift of an object floating in the water, this field is then used as the initial condition for the calculation of a model prediction. The constant repetition of this process, therefore, improves the quality of the prediction.
To ensure practice-oriented and effective developments of these observation and prediction systems, HZG works jointly on this project with the Federal Maritime and Hydrographic Agency of Germany (BSH, Bundesamt für Seeschifffahrt und Hydrographie) in Hamburg.