Satellite measurements of sea surface height

While Argo is a vital new contributor to monitoring of the state of the global ocean, in order to realise its full potential it has a degree of interdependence with other observing system elements. Foremost among these is Argo’s link with high precision satellite altimetry, which measures sea surface height. Since the early 1990s there has been continuous quasi-global altimetry coverage, starting with ERS-1 and 2 and the remarkable 13-year (1992-2005) Topex-Poseidon satellites, continuing to the present day with Jason-1 and 2. (The name of the Argo project reflects its synergy with the Jason satellite series. Argo was the ship in Greek mythology in which Jason sought the Golden Fleece.)

Satellite altimetry provides accurate estimates of both global and regional sea-level changes. However, both thermal expansion (from global warming) and addition of freshwater (from terrestrial ice-melt and water storage changes) contribute to sea-level changes. Argo observations provide estimates of the thermal expansion component, which is crucial to understanding the mechanisms behind observed sea-level changes. The higher resolution of the satellite altimeter data help to reduce uncertainties in estimates of ocean heat content change, using relationships between sea surface height and column-integrated ocean temperature (e.g. Willis et al., 2004; Lyman and Johnson, 2008). It has also been demonstrated that altimetry provides a means of identifying previously undetectable anomalies in the performance of individual floats, which will help to ensure that Argo data is of the highest quality.