The design and testing of small, low-cost GPS-tracked surface drifters

We have designed and constructed drifters appropriate for use in regions characterized by limited horizontal extent. The drifters follow the upper 30 cm of surface currents, but can be modified to follow water at any depth. The drifters store their latitude and longitude internally, and transmit their current latitude and longitude to a handheld Global Positioning System (GPS)-radio receiver, making their location and subsequent retrieval straightforward. A field test of six drifters in Hog Island Bay, Virginia, United States, in August 2003 was successful and led to several design improvements. With simple construction and a total materials cost of under U.S.$200, this design will make drifters an accessible part of interdisciplinary experiments, provide a potentially valuable educational tool, and make experiments that require large numbers of drifters more cost-effective.