Topex/Poseidon was launched on August 10, 1992, but the first altimetric measurements came later, on August 21, 1992 for Poseidon and September 1st, 1992 for Topex. Since September 23, 1992 (beginning of Cycle 1), the satellite provide continuously sea surface height measurements.
During the ten days of this first cycle, Topex/Poseidon collected more data about the oceans and their circulation than the previous 100 years of in-situ measurements. Now, 8 years after, we've got a huge harvest of information. The future, with Jason-1, is promising an even more precise and more complete view of the oceans.

See also:

• Missions: Topex/Poseidon
• Missions: Jason-1

Websites on this subject:

• Topex/Poseidon
    - Topex/Poseidon (Cnes) (in French)
    - Topex/Poseidon (Nasa/JPL)
• Jason-1
    - Jason-1 (Cnes)
    - Jason-1 (Nasa/JPL)