Jason-1 is a follow-on altimetric mission to the very successful TOPEX/Poseidon mission. It is a joint mission between NASA and CNES (French space agency). It launched December 7, 2001 and began data collection at January 15, 2002. Jason-1 is capable of measuring significant wave height, sigma0, dry and wet troposphere and ionosphere, which can be used to calculate sea surface height and anomalies and total electron content.
Jason-1 has a repeat period of approximately 10 days with 254 passes per cycle. A list of cycle start times can be found here.
Sometimes there may be anomalous or missing data. Occasionally Jason-1 must perform maneuvers to maintain orbit. This may cause anomalous values so a list of maneuvers is available here.
When the satellite detects something abnormal it will go into safehold and will turn off all instruments and no data will be collected. A list of safeholds and periods of no data collection can be found here.