There is a nice write up in Nature about the ARGO (Array for Real-time Geostrophic Oceanography). Argo is network of automonous floats, now numbering over 3000, that record temperature and salinity in the upper 2,000m of the water column. ARGO has greatly increased our knowledge of these factors that were based before on measurements from research vessels and merchant ships. Obviously, this restricts where the data come from and yields poor coverage for many avoided or ignored areas.
