Introduction

More than 20 years ago, NASA and the French space agency (CNES) collaborated on what became the first of a series of important oceanographic missions that have been measuring ocean surface topography from space ever since. 

Measuring Ocean Topography With TOPEX/Poseidon, Jason-1 and 2

This first mission, TOPEX/Poseidon, is no longer operational, having exceeded its expected lifetime of 5 years to provide more than 13 years of data. Two follow-on missions, Jason-1 and the Ocean Surface Topography Mission/Jason-2 (OSTM/Jason-2), launched in 2001 and 2008, respectively, and have extended the time series of data to more than 20 years. 

These satellites have enhanced our ability to monitor ocean eddies in near real time, and also to measure ocean wave height, providing considerable value for ship navigation and fisheries operations. More importantly, the consecutive 20 year altimetric record has drastically improved our understanding of climatic variability and climate events (e.g., the El Niño Southern Oscillation), providing measurements for global mean sea level, mesoscale circulation, and hydrology (i.e., lake and river levels). Such measurements will continue into the next decade through follow-on satellite missions such as Jason-3, Sentinel-6 Michael Freilich, and the Surface Water and Ocean Topography (SWOT) mission.