Using satellite data and coastal HF radar to map and validate sea surface currents and to detect ships in Skagerrak (SaRaCuS)

Research Project, 2014

There is today an almost total lack of real time data of surface currents in the seas surrounding Sweden. With information about the sea surface current field the drift of an oil spill can be forecasted as well as back tracked to its source, a missing person in the water might be found in time and saved, a lost container can be found and collisions be avoided and the transport of nutrients and hazardous substances can be estimated. Sea surface current fields can be estimated from satellite data but there is a need to validate the algorithms with independent current data. The aim of the project was to do this by using current data from coastal HF (High Frequency) radar systems in Skagerrak and thereby increase the usability of satellite data for sea surface currents in the Baltic Sea where coastal HF radar is less applicable due to the low salinity. SMHI runs operational ocean circulation models which are used in forecasting the sea state and for producing drift forecasts. Surface current fields with high resolution in time and space, obtained from satellite data and coastal HF radar data, can be used for ocean model validation. A further step would be to assimilate current fields into the models to improve the ocean forecasts.

There is an interest in strengthen the surveillance of the marine borders of Sweden and Europe and the detection and tracking of ships at the sea surface is particularly studied. Ship detection at large distances is currently an important area for development  since the range for micro radars, which is used today, is limited to the horizon. With both satellite radar and coastal HF radar it is possible to detect and track ships beyond the horizon. The aim of the project was to evaluate ship surveillance in Skagerrak with these techniques.

The aim of the project was to produce validated information on sea surface currents from satellites and to improve the routines for ship surveillance. A validated satellite product for sea surface currents has the potential to be used operationally at SMHI for validation as well as for assimilation. The project focused on the maximum cross correlation (MCC) method for satellite images in the thermal infrared (TIR) frequency band to estimate the velocity and direction of ocean surface currents.