Argo is a global array of 3,800 free-drifting profiling floats that measures the temperature and salinity of the upper 2000 meters (about 6562 feet) of the ocean. This allows, for the first time, continuous monitoring of the temperature, salinity, and velocity of the upper ocean, with all data being relayed and made publicly available within hours after collection.
Argo has grown to be a major component of the ocean observing system. It is a standard to which other developing ocean observing systems can look to. For example, Argo offers ideas on various topics such as how to collaborate internationally, how to develop a data management system and how to change the way scientists think about collecting data. Deployments began in 2000 and continue today at the rate of about 800 per year.
More on Argo here.