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Abstract

Surface current observations, using surface drifters, have been made for more than 2000 years with the earliest measurements made using visual sightings of natural and/or man-made floating objects within sight of land or from an anchored ship that served as a reference. The development of the GPS allowed for more accurate position fixing through satellites but was of limited the accuracy (~100m). The selective availability was removed in May 2000 that allowed for higher resolution position fixing (~10m). At this time, developing low-cost drifters to measure surface currents was possible. Over this period more than 500 drifters have been deployed. This talk will detail the how the drifters have been developed as different ‘off the shelf’ technologies have become available and the scientific discoveries through data analysis with an emphasis on low cost. Initial deployments, using ‘surf zone’ drifters were used to examine nearshore processes such as rip and longshore currents and dispersion. With the availability of ‘SPOT’ satellite trackers extended deployments in the open ocean was possible. In the past 3 years, more than 150 drifters have been deployed in the north-west shelf region that allowed for the understanding of surface circulation in the eastern tropical Indian Ocean. Analysis of these drifter tracks reveal major forcing mechanisms in the region through tides, winds (inertial currents), tropical cyclones and meso-scale eddies. An interesting result is that dispersion studies indicated that irrespective of the scales of the motion (nearshore, open ocean), dispersion follows the 4/3 law proposed by Richardson (1926).