drifter

A drifter (not to be confused with a float) is an oceanographic device floating on the surface to investigate ocean currents by tracking location. They can also measure other parameters like sea surface temperature, salinity, barometric pressure, and wave height. Modern drifters are typically tracked by satellite, often GPS. They are sometimes called Lagrangian drifters since the location of the measurements they make moves with the flow. A major user of drifters is NOAA's Global Drifter Program. Construction principle The major components of a drifter include surface floats for buoyancy, underwater drogues to ensure the drifter follows the movements of the water and is unaffected by wind, instruments (e.g., data collecting instruments, transmitters to transmit the collected data, and GPS devices), and waterproof containers for instruments. Drifters are a technological evolution of ocean current analysis historically performed through drift bottle experiments, which in turn were built on the principle of a message in a bottle. Types Drifters are typically either surface drifters, or deepwater drifters. Surface drifters remain in top meter of the water column, and deepwater drifters are suspended approximately 15 meters below the water surface to track sub-surface currents. Both types measure currents in the upper ocean. Surface Drifters The main type of surface drifter is the CODE drifter. The CODE drifter gets its name from the 1985 Coastal Dynamics Experiment (CODE), and it is also called a Davis drifter. It is designed to track the wind-driven surface currents in the upper meter of oceanic mixed layer.