The Full Picture

[

] 68

Argo data are subjected to automated quality checks

and made publicly available within about 24 hours of

collection at two Global Data Assembly Centers

(GDACs). Operational centres and other users may

acquire this near real-time data either from GDAC via the

Internet or from the World Meteorological Organization’s

Global Telecommunications System. A research-quality

version of the data is prepared by expert examination of

all float data, using internationally agreed protocols, and

is similarly available from the GDACs. The Argo

Information Centre maintains a searchable database of all

float positions, and serves the programme in many differ-

ent ways by facilitating communication and exchange

between national Argo programmes and users.

While the basic Argo float collects temperature and

salinity profiles in the upper 2 km of the oceans, tech-

nological advances will broaden the use and applications

of Argo in the future. Argo floats can carry additional

sensors for dissolved oxygen and other ocean proper-

ties. Several approaches are being tested to allow

sampling under seasonal ice cover. The present 2,000-

metre depth limitation could be extended with

modifications to the pressure hull and pumping system.

Finally, a sophisticated new version of the instrument

(the glider) with wings, a streamlined hull and active

Experiment (GODAE), and the Global Ocean Observing System

(GOOS). The strong consensus for a global Argo array was promoted

by national agencies as well as by scientists around the world, and

plans to begin deploying Argo floats developed rapidly. Initial deploy-

ments began in 2000, with regional arrays expanding and

technological hurdles being overcome in 2001-2003. By 2004 deploy-

ments were on a global scale and the target rate of around 800 floats

per year was achieved. As of mid-2007 there are 26 nations deploy-

ing floats in support of Argo, and the initial objective of a global

array of instruments at about 3° spacing has been reached.

How do Argo floats work?

Argo floats are made in several countries, and while there are differ-

ences in design, the basic concept does not vary. A float is launched

at the sea surface from a research vessel, commercial ship or aero-

plane. The float sinks to about 1,000 metres depth, and drifts with

ocean currents for ten days. After this interval, the float dives to

about 2,000 metres, and then ascends to the sea surface, measuring

temperature and salinity on the way up. At the sea surface, the data

are transmitted to a satellite and relayed to a ground station and data

centre. Meanwhile, the float again sinks to 1,000 metres to start a

new ten-day cycle. To achieve this ascent and descent, floats change

their buoyancy using a high-pressure pump that moves mineral oil

into an external rubber bladder for ascent, or draws it back inside the

instrument for descent.

The distribution of floats in the Argo array, August 2007

As of mid-2007, 26 nations were deploying floats in support of Argo.

The initial objective of a global array of instruments at about 3°spacing had been achieved

Source: Argo Information Centre – Mathieu Belbéoch

GEOSS C

OMPONENTS

– O

BSERVING

YSTEMS