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Float structure
 P ALACE Float predecessors

In 1960s in the Japan Sea were used Swallow floats. These floats were used extensively in investigations of the deep sea circulation and revealed for the first time the mesoscale currents and inertial variations in flow velocity. A low frequency version (~ 200 Hz) was developed for a tracking ship. These floats transmitted via the SOFAR channel to shore-based US-Navy listening station in the Atlantic ocean.

In the 1980s the sound sources were moved from the floats to moorings which transmitted to acoustic receivers on the floats. These floats are known as RAFOS.

In the late 1980s the World Ocean Circulation Experiment (WOCE) required global coverage with subsurface floats. This precluded acoustic tracking and resulted in the development of the Autonomous Lagrangian Circulation Explorer (ALACE), a neutrally buoyant float that would surface at regular intervals by inflating an external bladder, transmit temperature/pressure data and be positioned by the ARGOS satellite system and then return to its operating depth. A similar buoyancy-change mechanism is used in the ALFOS floats (are tracked as is the RAFOS).

Companion of the ALACE is the SLOCUM that derives the energy needed for buoyancy change from the temperature difference between the ocean surface and the ambient temperature at its operating depth. A prototype has been built.