Float Design
The critical capability of an Argo float is its ability to rise and descend in the ocean on a programmed schedule. The floats do this by changing their effective density. The density of any object is given by its mass divided by its volume. The Argo float keeps its mass constant, but by altering its volume, it changes its density. To do this, a hydraulic piston is used to push mineral oil out of the float and expand a rubber bladder at the bottom end of the float. As the bladder expands, the float becomes less dense than seawater and rises to the surface. Upon finishing its tasks at the surface, the float withdraws the piston and descends again.
An increasing number of the floats also carry other sensors, such as for measuring dissolved oxygen.
The antenna for satellite communications is mounted at the top of the float. Once the float reaches the surface, the float is essentially a spar buoy, allowing the antenna to poke above the sea surface for communication. The ocean is saline, hence an electric conductor, so that radio communications from under the sea surface are difficult.
The nominal life span of an Argo float is five years. After the internal batteries expire, the floats are allowed to sink to the ocean floor or wash ashore, though having a float wash ashore is very rare and unusual.
Read more about this topic: Argo (oceanography)
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