ACCURATE CURRENT MEASUREMENT USING DROGUED BUOYS EMPLOYING DECCA NAVIGATOR AND ARGOS

A major research program is under way in the North Sea organized by the United Kingdom's Natural Environment Research Council. The program contains detailed studies of tidal processes, frontal circulation, eddies, and mixing. For these studies, free-floating drogued buoys have been developed; they are equipped with two independent tracking systems-Decca Navigator and Argos. Decca Navigator, a hyperbolic radio navigation system with extensive coverage in Western Europe, provides accurate and frequent fixes, and the Argos satellite system is used to monitor progress in real time and to assist recovery. The low-power consumption microprocessor-based Decca Navigator receiver designed specifically for this application synchronizes to the precisely timed Decca transmissions and then goes into sleep mode, waking briefly at 10-min intervals to take position fixes. The position data acquired are stored in a 2-Mb memory card that has a three-month capacity at the 10-min rate. The recovery procedure, using both Argos and a small VHF beacon, is described, together with other recent developments of the system. A typical buoy track from a study in the North Sea is included.