space14.gifArgo Floats collect a series of about 200 pressure, temperature, salinity measurements on its way back up the water column.
Once the float reaches the surface, this data is transmitted to a satellite on a 10-day cycle.This cycle was designed to join up with the existing satellite measurements of the ocean's sea surface. These satellites, called Topex/Poseidon and Jason 1, measure changes in the surface topography of the ocean and it makes sense to combine this data with the data Argo Floats collect.
For more information about satellites here is a link to a wonderful site.
http://sealevel.jpl.nasa.gov/education/

Argo_annimation_2.gifGlobal Positioning System (GPS)
There are 2 main systems used.
In the past the Argos system has been favoured. This uses the Doppler effect and 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.
The negative side of this is damage to the Float on the surface in wild weather ( and the slight chance of being hit by a vessel while floating at the surface). Being on the surface for a long period can also change the ocean current measurement with interference of strong winds.
New technology is always improving and Argo Floats deployed now mostly use GPS and data communication using the **Iridium** satellites. 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. This two-way communication allows the researcher to change the cycle to shorter than 10 days if something different is occurring and more measurements are required.

How does a GPS work?