Observations are shown from an ocean radar system which operates in the VHF frequency band (100-180 MHz) and produce surface current measurements on grid scales of 50-200m over ranges up to 6-10 km. This is a scale of operation that is well suited to measurement tasks in Ports, harbours and coastal zones. Ocean radars commonly used for mapping surface currents in coastal zones operate in the HF frequency band and measure currents on grid scales of 3-6 km over distances of 100-200km.
The VHF ocean radar system consists of two stations which look at the same patch of ocean from different directions. Each station measures the radial component of the surface current at each grid point, and by combining data from both stations it is possible to produce maps of surface current vectors. Each station can cover a 60-degree sector of azimuth, and for wider coverage it is possible to use multiplexed receive antennas to double the size of the sector. The time to make the basic 60-degree sector for two stations is 10 minutes, and becomes 20 minutes for the wider 120 degree coverage.
Results are shown for sheltered coastal waters and for open coast line where there are breaking waves. This methodology is particularly appropriate for monitoring currents in congested port areas where fixed moorings may be compromised
