RAFOS float

They drift with these deep currents and listen for acoustic "pongs" emitted at designated times from multiple moored sound sources.

The name "RAFOS" derives from the earlier SOFAR floats,[2] which emitted sounds that moored receivers picked up, allowing real-time underwater tracking.

In important scientific aspects, as the study of global warming, ocean currents are found to greatly affect the Earth's climate since they are the main heat transfer mechanism.

They are the reason for heat flux between hot and cold regions, and in a larger sense drive almost every understood circulation.

This method works very well, and allows the use of small micro-processors, enabling the float itself to do the listening and computing, and a moored sound source.

The floats consist of 8 cm by 1.5 to 2.2 m long glass pipe that contain a hydrophone, signal processing circuits, a microprocessor, a clock and a battery.

The glass thickness is about 5 mm, giving the float a theoretical maximum depth of about 2700 m. The external ballast is suspended by a short piece of wire chosen for its resistance to saltwater corrosion.

[1] The electronics can be divided into four categories:[1] a satellite transmitter used after surfacing, the set of sensors, a time reference clock, and a microprocessor.

The clock is essential in locating the float, since it is used as reference to calculate the time travel of the sound signals from the moored emitters.

An isobaric float aims to follow a constant pressure plane, by adjusting the ballast's weight to attain buoyancy to a certain depth.

Then, because the speed of sound is known to 0.3% in sea, the position of the float can be determined to about 1 km by an iterative circular tracking procedure.

[1] The Argo project[6] is an international collaboration between 50 research and operational agencies from 26 countries that aims to measure a global array of temperature, salinity and pressure of the top 2000m of the ocean.

This project has greatly contributed to the scientific community and has issued many data that has since been used for ocean parameters cartography and Global change analysis.

In recent developments the floats have been able to measure different amounts of dissolved gases, and even to carry small experiments in situ.