There are four 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). Currently, Jason-2 is located on the former orbit of Topex/Poseidon (before 2002) and Jason-1 (before February 2009). The Jason-1's orbit is shifted midway between its original ground tracks (corresponding to those of Topex/Poseidon after 2002). Jason-1 and OSTM/Jason-2 also have a time lag of 5 days.
• One satellite - Envisat - with a longer repeat cycle (35 days) but tighter ground track spacing (90 kilometres at the equator), and another one, ERS-2, on the same track with a small time-lag (but no longer any onboard recorder).