4.2. Current altimetry missions

There are five altimetry satellites currently in service:
- Two satellites - Jason-1 and Jason-2 - with a relatively short repeat cycle (10 days), able to observe the same spot on the ocean frequently but with relatively widely-spaced ground tracks (315 kilometres at the equator). Jason-2 is on the same orbit as their predecessor, Topex/Poseidon (1992-2005), while Jason-1 has been shifted on a new orbit, mid-way between the previous one, with a 5-day time lag.
- One satellite - Envisat - with a longer repeat cycle (35 days) but tighter ground track spacing (90 kilometres at the equator).
- One satellite - Cryosat-2 - with an altimeter (Siral) ables to work with an interferometric mode, with a high orbit inclination of 92° to satisfy the scientific requirements for observing the poles and the ice sheets, and with an orbit non-sun-synchronous (commonly used for remote-sensing satellites).
- One satellite - HY-2 - with a 14-day orbit.