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Introduction to Argo

  An oceanic treasure hunt   What are Argo floats?
  3000 floats around the world   Where are the floats now?      


The oceans cover 71% of the surface of the beautiful blue planet Earth. Yet they are remote and inaccessible even to that half of the world's population who live within 200km of the shore.

To get a feel for that inaccessibility, imagine yourself standing on the seashore with a pair of binoculars. The sun is setting, and the full moon is rising in the ever-darkening sky.

Ancient greek trireme sailing a moon-lit sea
Jason's ship was probably a trireme, and ancient Greek ship like the one above, with sails and 3 rows of oars.

You look up towards the silvery moon. The area of the disk you can see is about 4 times the area of the Mediterranean Sea, about 1/20th of the area of the Pacific, and although the moon is 380,000 km away, you can clearly see the pattern of craters and mountains on its surface.

Now turn you binoculars to the sea just a few metres away. You can see the waves on the surface but nothing more. You can't see the fish and plankton that live in it, you can't see whether the sea floor is sandy or rocky, and you have no way of telling how deep it is. That is the challenge faced by ocean scientists - how to study what is happening beneath the surface of the Earth's oceans.

An oceanic treasure hunt

We are going to take you on a voyage, a voyage in which you will play an active part. You will learn about the oceans, and you will be able to see information from far beneath the surface at exactly the same time as scientists receive that information in their laboratories.

In Greek mythology Jason sailed the oceans on his ship, the Argo, in search of the treasure of the Golden Fleece. In the 21st century a fleet of about 3000 modern-day 'Argos' is searching for an even more important treasure - an understanding of how the oceans affect our lives and particularly how they influence the Earth's climate. Those modern 'Argos' are actually very clever and sophisticated robotic instruments. For reasons that will be explained we call them Argo floats.

Argo measurement cycle
Argo measurement cycle. Click on image for more.

What are Argo floats?

Argo floats are drifting cylindrical containers with instruments to measure the properties of sea water. The floats drift freely with the currents, measuring the temperature and salinity of the upper 2000 m of the ocean. They make it possible to monitor the temperature, salinity, and current velocity of the upper ocean continuously and receive the data within hours. Some floats also make other measurements.

The body of an Argo float is made of aluminium tubing. It contains electronics, pumps and many batteries. At the top are the sensors that measure temperature and salinity, and an antenna to transmit the data. At the bottom is a rubber bladder, which controls the depth of the float.

Soon after a float is launched it sinks to 1000m depth and then to 2000m, making measurements all the way. After 10 days it returns to the surface and transmits its measurements back via satellites. Soon after the measurements are available to scientists - and to you - on the Internet.   More about how an Argo float works.


Countryspacer spacerArea
France543,965 km2
Spain505,992 km2
Germany357,022 km2
Norway323,802 km2
Poland312,685 km2
Italy301,318 km2
U.K.242,900 km2
Greece131,957 km2
Bulgaria110,879 km2
Iceland103,000 km2
Portugal92,090 km2
Ireland70,273 km2
Netherlands41,543 km2
All Europespacerspacer10,180,000 km2

3000 floats around the world

Since November 2007 there have been just over 3000 floats operating and delivering their measurements every 10 days. 3000 seems like a large number, but then the ocean is a large place.

Quick questions


The area of the Earth's surface is 510,065,600 km2.
About 71% (or more accurately 70.8%) of this is ocean.
What is the area of the ocean surface?

Argo float


The surface area of the ocean is about 361 million km2.

510,065,600 km2




361,126,445 km2

Earth's surface area   70.8%
(70.8 of 100)
  Area of the ocean


Argo floats make measurements down to 2000 m depth.
84% of the ocean is deeper than 2000m.
What is the area of the ocean where Argo floats can operate?

Argo float


The area where Argo floats can operate is about 303 million km2.

361,126,445 km2




101,115 km2

Total area of the ocean
from question 1
(84 of 100)
  Area of the ocean
deeper than 2000m


Argo hopes to continue with about 3000 floats
by replacing floats that stop working.
What is the average area covered by one float?

Argo float


The average area covered by one float is just over 100,000 km2.

361,126,445 km2




101,115 km2

Area with woring floats
from question 2
divided by
3000 floats
Average area covered
by one Argo float


How does this area compare with the areas of the European countries in the table?

Argo float


It's equivalent to a little under 1/5 of Spain, 1/3 of Italy and about the same size as Iceland. If the floats were equally spaced, the entire area of Europe would only have 100 floats.

Where are the floats now?

The floats are not equally spaced however, as you can see if you look at the current position of the floats in Google Earth.

The image on the left shows Argo floats in the Atlantic January 2009 as seen in Google Earth. Click on the image to find out how to see where the Argo floats are now.

We can use the floats to look 'inside' the ocean and learn more about how the water moves. The float measurements also tell us how the temperature and salinity of the water change with depth. Data from floats in different parts of the world can help us understand how the oceans affect our weather and climate.

To show you how this is done, we have selected a small number of the 3000 floats that have long records and are in interesting areas of the ocean. Click here to see our selection of floats.   Please note: you need to have Google Earth installed on your computer for this link. If you are new to Google Earth, start with our page: How to use Google Earth to see the Argo Floats.

Link to the main Euro-Argo project website.