Gliders are relatively new ocean-measuring devices. Autonomous underwater vehicles, they glide in the waters with a payload of instruments onboard, measuring all the while temperature, salinity, currents, chlorophyll, pressure... Such instruments are typically presented as complementary to satellites - they are measuring underwater, where the satellites can't, but locally, when the satellites give global coverage (satellite altimetry, however, is a bit special among the space measurements, since it depends on what is in the whole water column, from top to bottom).

Thus, mixing altimetry and glider data can provide information not available with either one separately, for example about the way waters are moving vertically.