Argo world 

Frequently Asked Questions

*  What is Argo?
Argo is an international project to collect information on the temperature and salinity of the upper part of the world's oceans. Argo uses robotic floats that spend most of their life drifting below the ocean surface.  They make temperature and salinity measurements when they come up to the surface and after transmitting their data to satellites, they return to depth to drift for 10 days.  Currently, there are roughly 3000 floats producing 100,000 temperature/salinity profiles per year.  The floats go as deep as 2000m. To learn more, visit the "About Argo" page.

*  Why is it called Argo?
In Greek mythology, Argo was the ship in which Jason and theArgonauts set sail to search for the golden fleece.  Argo floats sail the 21st century seas and Argo is teamed with a satellite called JASON-1 that measures the shape of the ocean surface.  Data from Argo and JASON-1 together will monitor the ocean currents, the oceans' transport of heat and freshwater around the globe and sea-level rise.  

*  What do the floats look like and how do they work?
The floats have a pressure case made of aluminium that is about 1.3m long and about 20cm diameter.   They weigh about 40kg.  On the top is an antenna to communicate with the satellites that fix the float's position and receive the data. Also on the top are the temperature and salinity sensors.  At the bottom of the float in a protective cover is a bladder that is connected to the inside of the float.  The floats are designed so that with the bladder empty they have the same density as seawater at the depth at which they drift.  They are also designed to be less compressible than sea water.  This keeps them stable at depth. 

The floats are put in the ocean from ships or aircraft and sink to depth.  After 10 days oil is pumped into the bladder and drives the float to the surface.  At the surface it is positioned by satellites and downloads its temperature /salinity profile. The bladder then deflates and the float sinks back to depth to repeat the cycle. To learn more, visit the "How Argo Floats Work" page.

*  How are the floats powered and how long do they work for?
The floats are powered by batteries.  Many use manganese/alkali batteries like you can buy in shops, but most floats that are deployed now use higher-powered lithium batteries.  The floats are designed to do about 140 cycles and so should last almost 4 years. The life depends on the depth to which they profile and the surface water density in which the float is operating. (If the surface water has low density, more oil must be pumped to drive the float to the surface). To see plots on float lifetimes, go the the Argo Information Centre.

*  Who uses the data?
Argo data are used by weather and climate centers to help understand the way the oceans affect climate.  These centers are working to improve forecasts of El Nino events and to understand other climate features like monsoons and global warming.   Argo has now become the main source of subsurface temperature and salinity from the deep oceans. See the Uses of Argo Page for more details on the operational and research uses of Argo data.   

The most important thing about Argo data is that it is FREE to anyone wishing to use it.  The data can be obtained from two global data servers, one in France and one in the USA. To learn more, visit the "Argo data and how to get it" page.

The temperatures in the Argo profiles are accurate to ± 0.002°C and pressures are accurate to ± 2.4dbar. For salinity,there are two answers. The data delivered in real time are sometimes affected by sensor drift. For many floats this drift is small, and the uncorrected salinities are accurate to ± .01 psu. At a later stage, salinities are corrected by expert examination, comparing older floats with newly deployed instruments and with ship-based data. Corrections are made both for identified sensor drift and for a thermal lag error, which can result when the float ascends through a region of strong temperature gradients.

Following this delayed- mode correction, salinity errors are usually reduced further and in most cases the data become good enough to detect subtle ocean change. The estimated accuracy of the delayed mode quality controlled salinity can be found in the PSAL_ADJUSTED_ERROR fields in the D profile files. If the salinity is found to be questionable even after delayed mode adjustment, there error and the qc flag are adjusted to higher than usual to make users aware of this. Therefore, users should use the *_ADJUSTED_ERROR and *_ADJUSTED_QC fields in the profile files to filter the data set to remove less accurate measurements.

This goes for all the parameters measured. While the temperature and pressure sensors are highly accurate, they may still have errors, leading to higher adjusted error fields and qc flags.

In general, data that are considered bad and unadjustable are marked with a qc flag of '3' or '4'. These bad data should not be used in any scientific applications.

Each float costs about $15,000 USD and this cost about doubles when the cost of handling the data and running the project is taken into account.  The array has roughly 3000 floats and to maintain the array, 800 floats will need to be deployed each year.  Thus the approximate cost of the project is 800 x $30,000 = $24m per year.  That makes the cost of each profile around $200. 28 countries have contributed floats to the array with the USA providing about half the floats.

The Argo array reached 3000 floats in November 2007, and can be maintained at that level as long as national commitments provide about 800 floats per year. The need for global Argo observations will continue indefinitely, though the technologies and design of the array will evolve as better instruments are built, models are improved and more is learned about ocean variability.

Argo has an international Steering Team and a Data Management Team made up of scientists from countries involved in Argo. An Argo Technical Coordinator monitors the array and registers each float deployment in accordance with international agreements. Argo also has an international Director, Dr. Howard Freeland. Each country finds its own funding and sets its own priorities for where floats are deployed in consultation with other countries.To learn more, visit the "Argo Project Office" page.

*  What happens when floats stop working?
Most floats will "die" when the battery is too weak to pump the float to the surface.  These floats will drift around in the deep ocean until the pressure case corrodes and the float falls to the sea bed.  However a small number will washup on the beach or, vary rarely, be caught in nets.  Floats have labels (in many languages) on them telling the finder, what to do with the float.

The floats make no noise in the ocean and they do not contain materials that are not found elsewhere in the oceans.  We take care to ensure that they are handled properly if they are found by fishermen or beachcombers.  They are small and light enough to pose no significant hazard to ships and boats.

  Argo label
*  What should I do if I find a float?
In the rare case that a float is found on a beach we can learn a great deal from it about why it failed.  First look for the float's identification.  The float should have a label (shown here at right) with instructions in many languages.

If you can safely do so, move the float to a location where it can be stored without getting too hot and where it cannot be interfered with by other people.

Follow the instructions on the label and inform the Argo Information Centre in France (by, Fax +33 5 61 75 10 14 or telephone +33 5 61 39 47 30)  giving information on the float identification numbers, where and when the float was found and where it is stored.  If this is not possible please ask the local police or coast guard to contact Argo. Arrangements will then be made to return the float to its owner.

Yes, Argo has a blog at The blog is used to discuss issues like warming of the ocean, climate,etc. Check out the blog and add your own thoughts.

If you have general questions about Argo, please send them to
If you have more technical questions about the data, please look at the support website or e-mail the support desk (