Argo world 

Argo Floats

Argo is an international collaboration that collects high-quality temperature and salinity profiles from the upper 2000m of the ice-free global ocean and currents from intermediate depths. The data come from battery-powered autonomous floats that spend most of their life drifting at depth where they are stabilised by being neutrally buoyant at the "parking depth" pressure by having a density equal to the ambient pressure and a compressibility that is less than that of sea water. At present there are several models of profiling float used in Argo. All work in a similar fashion but differ somewhat in their design characteristics. At typically 10-day intervals, the floats pump fluid into an external bladder and rise to the surface over about 6 hours while measuring temperature and salinity. Satellites or GPS determine the position of the floats when they surface, and the floats transmit their data to the satellites. The bladder then deflates and the float returns to its original density and sinks to drift until the cycle is repeated. Floats are designed to make about 150 such cycles.

Argo Mission

The standard Argo mission is a park and profile mission where the float descends to a target depth of 1000m to drift and then descends again to 2000m to start the temperature and salinity profile. In the beginning of 2014, 80% of floats profile to depths greater than 1500m. Another 12% profile to between 1000 and 1500m.

Argo Float Models

The Argo array is currently comprised of several float models: the PROVOR and the ARVOR built by NKE-INSTRUMENTATION in France in close collaboration with IFREMER, the APEX float produced by Teledyne Webb Research, the SOLO float designed and built by Scripps Institution of Oceanography, USA and the S2A float built by MRV Systems in the USA.

The ARVOR is a new generation PROVOR float and the S2A is a new generation SOLO float. The NAVIS is a new float being built by Sea-Bird in the USA.

The SBE temperature/salinity sensor suites is now used almost exclusively. In the beginning, the FSI sensor was also used. The temperature data are accurate to a few millidegrees over the float lifetime. For discussion of salinity data accuracy please see the Data FAQ.

Argo Data Transmission

As the float ascends, a series of about 200 pressure, temperature, salinity measurements are made and stored on board the float. These are transmitted to satellites when the float reaches the surface. For floats using high speed communications with more bandwidth capabilities, measurements are taken more frequently, often up to every 2db, resulting in several hundred measurements per profile.

For 70% of floats in the Argo array the data are transmitted from the ocean surface via the Système Argos location and data transmission system. 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 using positions from the Global Positioning System (GPS) and data communication using the Iridium satellites now comprises 30% of the Argo array. Iridium is becoming a more attractive option as it allows more detailed profiles to be transmitted with a shorter period at the surface and even two-way communication. In 2013, 60% of floats were been deployed with Iridium antennas and 40% with Argos antennas.