More on Profiling Floats...

What’s an Argo float?

The Argo float is an autonomous instrument of subsurface which measures the temperature and salinity in the heart of the oceans.

The float is programmed in advance and is deployed from research vessels or ship of opportunities (deployments from plane are also possible). Then it starts ten days cycles, during several years, until exhaustion of its energy. Each cycle breaks up into two times: a descent towards the immersion of instruction to 1000m, then a drift with the liking of the currents until the immersion of beginning of profile with 2000m. It starts then its increase towards surface by carrying out its measurements. Once emerged, it transmits its data before setting out again for a new cycle.

How does an Argo float work?

During its descent, the density of the float increases less quickly than that of surrounding sea water. It is stabilized with a depth to which it is maintained naturally in balance, without energy requirement. A modification of its density enables him to reach a new balance. The float then implements a mechanism of modification of its volume, its constant mass remaining. The system functions thanks to a ballast and a reserve of oil. The deflation of the ballast, via a hydraulic actuator, makes sink the float and the reverse makes it ascent. The sensor is located in the upper part of the float. Salinity is deduced from measurements of conductivity, temperature and pressure. The data transmission to ground mainly uses the Argos data collection and localization satellite system. Iridium system is used when more data need to be transmitted.

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How the settling occurs for such equipment?

The float completely autonomous, a bit like satellites, is developed a little according to a methodology of rigorous quality assurance. The phases of design and tests are very thorough. The traditional operating processes and ranges are taken into account. Low fuel consumption, the control of materials, the precision of the sensor and stability in time are essential parameters. The development requires characterizing perfectly the embarked software, the performances and the limits of the material. Tests out of basin and hyperbare box constitute the ultimate tests. The three principal floats used in the program are the APEX and the SOLO (USA) and Provor, developed by Ifremer with the Kannad company who ensures its manufacturing and marketing. A new version of the Provor float called Arvor is operational since mid 2008. It is lighter and easier to deploy. When Arvor is fully operational, Provor will continue to provide multi-sensor (e.g. O2, biology) capabilities. The German company Optimare has also the NEMO-floats based on the successful design of the SOLO-floats.