With the successful launch of Jason-1 and Envisat, we now have five altimetry satellites in orbit. These two latest additions to the constellation, orbiting very near their predecessor Topex/Poseidon, have not yet acquired new data but they will be phased relative to each other once validation is complete. This means we will have:

• two satellites-Topex/Poseidon and Jason-1-with a fairly short orbital cycle (10 days), able to revisit the same point quite frequently but acquiring measurements spaced 315 kilometers apart at the Equator;
• two satellites-ERS-2 and Envisat-with a longer cycle (35 days) but able to acquire measurements on a tighter grid (90 km spacing at the Equator);
• and one satellite-GFO-somewhere "in between" (with a 17-day cycle and a distance between adjacent ground tracks of 160 km at the Equator), following the footsteps of its predecessors Seasat (1978) and Geosat (1985-1990).

The ERS - Topex/Poseidon tandem has already significantly improved spatial and temporal resolution of satellite data. As a result, we can see ocean circulation at a scale of 100 kilometers and monitor its variations. Now, the aim is to ensure the continuity of this system in the long term and to improve it if possible by always operating several satellites together. In the medium term, we are looking to track fairly rapid oceanic variations (less than 10 days) at scales below 100 kilometers, if possible near coastlines.

See also:

• Data: Ssalto/Duacs
• Altimetry: High-precision altimetry with satellites working together
• Altimetry: Future technology improvements
• Missions

Websites on this subject:

• Report of the High-Resolution Ocean Topography Science Working Group Meeting