Simulations with dispersion models and especially the tracer approach applied here provide highly detailed results on the spreading and mixing of substances in the water as well as on drifting objects. Tracer simulations can be simplified explained by marking a water mass or an area in the computer and simulate its evolution in space and time. In nature this would be similar when marking water with dye or drifters which, however, can be done only in very rare experiments.

For the simulation the dispersion model uses forecasts and results produced by the local or regional models like currents, water levels and wind. In coastal and tidal areas the fate and paths of the tracers depend very much on location and start time of the simulation. The variations of the behaviour and locations of such tracer ensembles in natural waters are almost infinite.

As an illustrative example we have simulated here a series of dispersion cases for an identical release (starting) position at the southern tip of the island of Amrum but with different start times. Four cases are overlaid in one display and the corresponding tracer distributions are plotted with different colours (blue at first, red 3, purple 8 and yellow 11 hours later). One can clearly see large differences in the spreading and mixing of the tracers.

Correspondingly in nature different areas are affected in case of accidental pollutions or an overboarded seaman will drift in other directions. Such information is extremely useful for pollution response but also for search and rescue (SAR) operations. As it is almost impossible to map all relevant dispersion cases the dispersion model in the OMS can be invoked on demand respectively when an emergency or accident should happen. By this associated forecasts and information is provided in time to support decision taking and operation control.