Mission
TOPEX/Poseidon was an altimetric mission that measured significant wave height, mean sea surface, sigma0 (which can be converted to wind speed), and all the parameters needed to calculate sea surface height anomalies.  It launched August 10, 1992 and began collecting data September 25, 1992 ( cycle 1). TOPEX/Poseidon’s last cycle was 481 (October 8, 2005). TOPEX/Poseidon had an orbit accuracy of 4.2 cm. A list of the TOPEX/Poseidon cycles by date is available at: http://podaac.jpl.nasa.gov/DATA_CATALOG/tp_cyclelist.txt

Temporal resolution
It takes approximately 10 days for TOPEX/Poseidon to complete a cycle that surveys the entire Earth. Each cycle consists of 254 passes, which is half an orbit around the Earth and contains ~56 minutes of data. There is ~1 second between measurements.

Spatial resolution
TOPEX/Poseidon surveys from 66.15° to -66.15°.  The along track resolution is 0.0001° in latitude and 0.05° in longitude. A table showing the equator crossing for each pass is available at: ftp://podaac.jpl.nasa.gov/pub/sea_surface_height/topex_poseidon/mgdrb/doc/uhmgdrb/html/uhsec02.htm

Documentation
Altimeter Ocean Pathfinder (NASA/GSFC): ftp://podaac.jpl.nasa.gov/pub/documents/dataset_docs/altimeter_ocean_pathfinder.html

Known Problems
There are times when the TOPEX/Poseidon satellite entered safehold-mode, and no data was collected as a result.  A list of safing events is available at http://podaac.jpl.nasa.gov/DATA_CATALOG/tpsafehold.txt. The satellite also performed a series of maneuvers to ensure orbital accuracy.  A list of maneuvers is available at http://podaac.jpl.nasa.gov/DATA_CATALOG/tp_maneuver.txt

Various conditions, such as heavy rain or ice, may affect altimetric measurements.  Known environmental and geophysical problems are flagged to allow researchers to easily evaluate these measurements.  A description of the TOPEX/Poseidon flags is available in the TOPEX/Poseidon IGDR and GDR.  ftp://podaac.jpl.nasa.gov/pub/sea_surface_height/topex_poseidon/mgdrb/doc/uhmgdrb/html/uhsec03.htm

TOPEX-A altimeter operated from cycles 1-235.  In mid 1997, it was determined that there was a degradation in the point target response which impacted the significant wave height.  In February 1999, TOPEX-A was turned off and the redundant backup input titleimeter, TOPEX-B altimeter, was turned on.  Subsequent calibration to assess the data resulted in keeping TOPEX-B on for cycle 236 and all subsequent cycles.  Cycle 235 was the last cycle using TOPEX-A.

In the MGDR version B data cycles 1-190 there were some small errors, mostly the incorrect default values were placed in the data, but the flags are correct.  A full list of the errors can be found at http://podaac.jpl.nasa.gov/DATA_CATALOG/user_mgdrberrors.doc

Early Pointing Angle Problems
From cycle 1 through cycle 8 pass 189 (September 23 through December 8, 1992, day of year, DOY, 343), the satellite attitude control system was not properly calibrated. This resulted in pointing the altimeter relatively far from nadir (typically 0.3, but up to 0.6) with a sinusoidal signature over each pass much of the time. Since the pointing angle/sea state corrections are less accurate for angles larger than about 0.3 and the geometric pointing correction cannot be done, these data will be less accurate than later data. The pointing calibration was improved on 1992 DOY 353 and 357 and 1993 DOY 046, but these changes were minor compared to the initial calibration on 1992 DOY 343.  The user may want to begin analysis on data beginning with cycle 11.

Frequently Asked Questions
http://podaac.jpl.nasa.gov/FAQ/index.html#altimetry

Citations/References
MacMillan, D., Y. Bock, P. Fang, B. Beckely, C. Ma. Calibration of the TOPEX and Jason-1 altimeter microwave radiometers using VLBI and GPS derived tropospheric delays. http://sealevel.jpl.nasa.gov/science/invest-macmillan.html