February 24, 2009

Surveying Earth’s oceans: Jason-1 and Jason-2 join forces

After a 6-month cross-calibration phase, Jason-2 has been moved into the orbit of its predecessor Jason-1. The 2 ocean-observing satellites will now fly in tandem on parallel ground tracks until Jason-1 reaches the end of its mission life, thereby doubling ocean data coverage.

Doubling ocean data coverage

Saturday 14 February, Jason-1 finally moved aside and left its orbit to its successor Jason-2, launched on 20 June 2008.

Launched end 2001, the Jason-1 mission was scheduled to last only 5 years but has been continuously extended due to its exceptional performance.

Jason-2 is now in Jason-1’s old orbit, whereas Jason-1 has been moved to a new orbit to double coverage of the ocean surface,” explains Jacqueline Perbos, Jason-2 Project Leader at CNES.

The 2 satellites will fly in tandem on parallel ground tracks.


This is because during the 2 hours it takes the Jason satellites to orbit Earth, the planet rotates eastwards. The resulting “ground track” of the satellites therefore cannot cover the entire surface of the globe.

Jason-1’s new orbit is midway between 2 adjacent Jason-2 ground tracks.

The resulting resolution is equivalent to that from a Jason satellite orbiting Earth in only 1 hour.

These orbital manoeuvres brought Jason-2’s calibration and validation phase to an end. For more than 6 months, Jason-2 trailed just 55 seconds behind its predecessor to enable scientists to acquire near-simultaneous measurements to precisely calibrate the satellite’s instruments. The results thus achieved are very good.

Complex manoeuvres handled from Toulouse

The change of orbit was handled by teams at the CNES mission control centre in Toulouse.

The process began with 2 manoeuvres on 26 and 27 January. We lowered Jason-1’s orbit by 20 km, to move it away from Jason-2,” explains Gérard Zaouche, who coordinated operations.

We then let it drift before repositioning it in its final operating orbit, 162° from Jason-2, bringing it back up 20 km to the same altitude as before.”

Three manoeuvres, on 4, 6 and 14 February, were required to accomplish this delicate task.

The Jason programme aims to characterise ocean currents, analyse ocean seasons, probe tides and track variations in sea level.

Launched 20 June 2008, the Jason-2 satellite is a partnership of CNES, NASA, NOAA and Eumetsat. The possible launch of a Jason-3 satellite is under discussion.

More about