A Davis drifter is an instrument designed to measure wind-driven surface currents. It has four major components: (1) body, (2) sails, (3) floats, and (4) a data collection/transmitter package. The body, which is a waterproof tube about 3 feet long and 10 inches wide, holds the collection/transmitter package. The sails extend out from the body as four pairs of cloth or vinyl “arms” with about 3 square feet of total sail area. The sails move the drifter along with the prevailing currents. The four floats are attached by ropes to the body of the drifter, keeping it suspended a few feet beneath the surface so that the drifter is not directly affected by the wind or waves.
The drifter’s transmitter sends signals to a polar orbiting satellite that calculates its position and relays this information to a receiving station. A typical drifter will transmit data for about one year before its power supply expires.