How Floats Works
At present there are three models of profiling float used in Argo. They are the PROVOR built by MARTEC in France , the APEX float produced by Webb Research Corporation , USA and the SOLO float designed and built by Scripps Institution of Oceanography, USA.
All work in a similar fashion but differ somewhat in their design characteristics. The floats spend a cycle period (typically 10 days) at the “parking depth” (nominal 1000m) where they are stabilized by having a density equal to the ambient pressure and a compressibility that is less than that of sea water. After 10 days, they descend to the “profile depth” (nominal 2000m) and begin a profile from this depth. All ascend and descend by pumping oil in and out of an external bladder.
Temperature, salinity and pressure of the sea water are measured during ascent. Two temperature/salinity sensor suites are used - SBE , and FSI .
As the float ascends, 200 pressure, temperature and salinitymeasurements are made and recorded on board. These are transmitted to satellites when the float reaches the surface.
For most floats in the Argo array the data are transmitted from the ocean surface via the Système Argos location and data transmission system (see also Service Argos Inc. ). The data transmission rates are such that to guarantee error free data reception and location in all weather conditions the float must spend between 6 and 12 hrs at the surface. Positions are accurate to ~100m depending on the number of satellites within range and the geometry of their distribution.
An alternative system to Argos has been tested using positions from the Global Positioning System (GPS) and data communication using the Iridium and Orbcomm satellites. This allows more detailed profiles to be transmitted with a shorter period at the surface and even two-way communication.
