Skip to main content

TOPEX/Poseidon was a joint altimetric mission between NASA and the Centre national d'études spatiales (CNES), the French space agency. It operated until Oct. 18, 2005, and collected 481 cycles of data. TOPEX/Poseidon was capable of measuring significant wave height, sigma naught (sigma0), dry and wet troposphere, and ionosphere, which can be used to calculate sea surface height and anomalies and total electron content.

TOPEX/Poseidon had a repeat period of approximately 10 days with 254 passes per cycle.

TOPEX/Poseidon began a drift maneuver on August 15, 2002, cycle 365, pass 111, and ended on September 16, 2002, cycle 368, pass 171. During this time, the satellite moved to a different orbit so that it and Jason-1 (which remained on the original orbit) would survey the Earth in a shorter amount of time and give a higher spatial resolution. Lists of cycle start times, maneuvers performed to maintain orbit, safe holds, and periods of no data collection are provided in the "Documentation" tab.

Learn more about TOPEX/Poseidon

Type

Earth Observation Satellite

Data Center

PO.DAAC

Launch

August 10, 1992

Objective

Measure ocean surface topography
Semi-major axis7,714.43 km
Eccentricity0.000095
Inclination66.04°
Argument of periapsis90.0°
Inertial longitude of the ascending node116.56°
Mean anomaly253.13°
Reference altitude1,336 km
Nodal period6,745.72 sec
Repeat period9.9156 days
Number of revolutions within a cycle127
Number of passes within a cycle254
Equatorial cross track separation315 km
Ground track control band+1 km
Acute angle at Equator crossings39.5°
Longitude of Equator crossing of pass 1, cycles 1-36599.9249°
Longitude of Equator crossing of pass 1, cycles 369-onward98.5°
Inertial nodal rate-2.08°/day
Orbital speed7.2 km/s
Ground track speed5.8 km/s

Switch Between TOPEX-A and TOPEX-B

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 altimeter, 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.

Errors in MGDR-B

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. View a full list of the errors.

Early Pointing Angle Problems

From cycle 1 through cycle 8 pass 189 (23 September through 8 December 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.

Sigma0 Calibration

View a list of calibrations for the TOPEX backscatter.

The calibrations are provided to improve the sigma0 values provided by the project that are found in the Geophysical Data Record (GDRs). If you are using the merged GDRS, the calibrations have been applied to cycles 1-132, otherwise you need to apply the calibrations to the other cycles yourself. If you are applying the Generalized Predictive Control (GPC) correction to the GDR, it contains the calibration corrections.

Instruments Aboard TOPEX/Poseidon

Related Platforms

Jason-1

The Jason-1 Earth satellite mapped sea level, wind speed and wave height, provided new insights into ocean circulation, tracked rising seas, and enabled more accurate weather, ocean, and climate forecasts.
Jason-3

Jason-3 continues the work started by the TOPEX/Poseidon, Jason-1, and OSTM/Jason-2 satellite missions to measure ocean surface topography.
OSTM/Jason-2

The third in a U.S.-European series of satellite missions designed to measure sea surface height.

Frequently Asked Questions

Earthdata Forum

Our online forum provides a space for users to browse thousands of FAQs about research needs, data, and data applications. You can also submit new questions for our experts to answer.

Submit Questions to Earthdata Forumand View Expert Responses

Earthdata
Forum