The need for a precision current-tracking system that could he deployed for up to 12 months as part of the U.K. Natural Environment Research Council's North Sea Project led to the development of a position-logging drifting buoy, which employs both the Decca Navigator and Argos systems.

A specially designed Decca Navigator receiver within the buoy computes and logs position fixes, which are accurate to within tens of meters under optimal conditions. After recovery of the buoy, these fixes are transferred to an external computer for analysis and plotting.

Real-time position monitoring (to a lower accuracy) is provided by an on-board Argos platform transmitter terminal. This also enables the buoy to be recovered on completion of the trials.

The technical capabilities of the drifting buoy are described, and preliminary results, obtained during deployments of nine buoys in the vicinity of a tidal mixing front in the North Sea are presented.

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