Precise satellite altimetry, orbit determination and location missions have transformed the way we view Earth and its oceans. Highly accurate altimetry measurements from Topex/Poseidon and Jason made possible by the Doris system give us the ability to observe sea surface height systematically.

Since 1986, these missions have been providing vital information for an international user community. Besides international programs dedicated to studying global oceans and climate, such as Woce, WCRP, Clivar, Goos and others working on the El Niño phenomenon (Toga), ocean forecasting projects such as Godae and Mercator are now getting underway. All these programs call for high-quality altimetry measurements, which are merged with other data to obtain the broadest picture possible of the underlying mechanisms at work, and assimilated in ocean and climate prediction models. What is more, precise satellite altimetry, orbit determination and location missions are also helping to define an international reference system-essential for locating any point on the Earth's surface accurately.