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Description

The TOPEX/POSEIDON Geophysical Data Record (GDR) contains global coverage altimeter data. The objective of the TOPEX/POSEIDON mission, launched in August 1992, is to determine ocean topography with a sea surface height measurement precision of 3 cm and a sealevel measurement accuracy of 13 cm. The dataset contains measurements from two altimeters, a NASA dual frequency (Ku and C band) instrument similar to the Geosat altimeter, and a French space agency (CNES) instrument which is a proof-of-concept solid-state altimeter (Ku band). It also contains Sea Surface Height (SSH), significant wave height, ionospheric correction, tides and other geophysical corrections. It is emphasized that this product is considered research data because of the form and content of the data. The data consist entirely of files comprising headers and data records which contain over a hundred parameters for each second. It is swath data and there are no images. Analysis software is the responsibility of the user. Calculation of sea surface height anomalies from the altimeter range and environmental corrections is the responsibility of the user. The data are arranged in 10 day cycles that are separated into 254 passes, each about 56 minutes.

Version Description

Reprocessed Geophysical Data Record (GDR) Version F

Product Summary

Platforms
TOPEX/POSEIDON
Instruments
ALT (TOPEX) ,
TMR
Projects
TOPEX/POSEIDON
Spatial Extent

N: 66 S: -66 E: 180 W: -180

Coordinate System
GEODETIC
Granule Spatial Representation
GEODETIC
Temporal Extent
1992-10-13 to 2005-10-04
Data Partner
Physical Oceanography Distributed Active Archive Center, Jet Propulsion Laboratory, NASA (NASA/JPL/PODAAC)
Concept ID
C2599212091-POCLOUD
Data State
COMPLETE
Number of Files/Granules
117669
Processing Level
2
Published
Science Keywords
Sea Surface Height ,
Significant Wave Height

Citation

Citation is critically important for dataset documentation and discovery. This dataset is openly shared, without restriction, in accordance with the EOSDIS Data Use and Citation Guidance.

Copy Citation

TOPEX/POSEIDON. (2023). TOPEX/POSEIDON Geophysical Data Record Version F [Data set]. NASA Physical Oceanography Distributed Active Archive Center. https://doi.org/10.5067/TPXPS-GDRF1 Date Accessed: 2026-06-06

Documents

Variables

The table below lists the variables contained within a single granule for this dataset. Variables often contain observed or derived geophysical measurements collected from a variety of sources, including remote sensing instruments on satellite and airborne platforms, field campaigns, in situ measurements, and model outputs. The terms variable, parameter, scientific data set, layer, and band have been used across NASA’s Earth science disciplines; however, variable is the designated nomenclature in NASA’s Common Metadata Repository (CMR). Variable metadata attributes such as Name, Description, Units, Data Type, Fill Value, Valid Range, and Scale Factor allow users to efficiently process and analyze the data. The full range of attributes may not be applicable to all variables. Additional information on variable attributes is typically available in the data, user guide, and/or other product documentation.

For questions on a specific variable, please use the Earthdata Forum.

Name Description Units Data Type Fill Value Valid Range Scale Factor Offset
sig0_numval_c Number of 20 Hz C-band MLE3 backscatter coefficient measurements (sig0_20hz_c) used to generate 1 Hz backscatter coefficient. count byte 127 0 to 20 1 N/A
sig0_numval_ku Number of 20 Hz Ku-band MLE4 backscatter coefficient measurements (sig0_20hz_ku) used to generate 1 Hz backscatter coefficient. count byte 127 0 to 20 1 N/A
sig0_numval_ku_mle3 Number of 20 Hz Ku-band MLE3 backscatter coefficient measurements (sig0_20hz_ku_mle3) used to generate 1 Hz backscatter coefficient. count byte 127 0 to 20 1 N/A
sig0_rms_c RMS of 20 Hz C-band MLE3 backscatter coefficient measurements. Only valid 20 Hz measurements are used to compute this element. dB short 32767 N/A 0.01 N/A
sig0_rms_ku RMS of 20 Hz Ku-band MLE4 backscatter coefficient measurements. Only valid 20 Hz measurements are used to compute this element. dB short 32767 N/A 0.01 N/A
sig0_rms_ku_mle3 RMS of 20 Hz Ku-band MLE3 backscatter coefficient measurements. Only valid 20 Hz measurements are used to compute this element. dB short 32767 N/A 0.01 N/A
sig0_used_20hz_c Map of valid points from sig0_20hz_c used to compute 1-Hz C-band backscatter coefficient, sig0_c. N/A byte 127 N/A 1 N/A
sig0_used_20hz_ku Map of valid points from sig0_20hz_ku used to compute 1-Hz Ku-band backscatter coefficient, sig0_ku. N/A byte 127 N/A 1 N/A
sig0_used_20hz_ku_mle3 Map of valid points from sig0_20hz_ku_mle3 used to compute 1-Hz Ku-band backscatter coefficient, sig0_ku_mle3. N/A byte 127 N/A 1 N/A
solid_earth_tide Calculated using Cartwright and Tayler tables and consisting of the second and third degree constituents. The permanent tide (zero frequency) is not included. See TOPEX User Handbook. m short 32767 N/A 0.0001 N/A
ssha altitude of satellite (altitude) - Ku-band MLE4 range (range_ku) - Ku-band MLE4 sea state bias correction (sea_state_bias_ku) - Ku-band MLE4 ionospheric correction (iono_cor_alt_ku) - radiometer wet tropospheric correction (rad_wet_tropo_cor) - model dry tropospheric correction (model_dry_tropo_cor_zero_altitude) - dynamic atmosphere correction (dac) - geocentric ocean tide height (ocean_tide_fes) - non-equilibrium long-period ocean tide height (ocean_tide_non_eq) - internal tide (internal_tide_hret) - geocentric pole tide height (pole_tide) - solid earth tide height (solid_earth_tide) - mean sea surface (mean_sea_surface_cnescls). m short 32767 N/A 0.001 N/A
ssha_mle3 altitude of satellite (altitude) - Ku-band MLE3 range (range_ku_mle3) - Ku-band MLE3 sea state bias correction (sea_state_bias_ku_mle3) - Ku-band MLE3 ionospheric correction (iono_cor_alt_ku_mle3) - radiometer wet tropospheric correction (rad_wet_tropo_cor) - model dry tropospheric correction (model_dry_tropo_cor_zero_altitude) - dynamic atmosphere correction (dac) - geocentric ocean tide height (ocean_tide_fes) - non-equilibrium long-period ocean tide height (ocean_tide_non_eq) - internal tide (internal_tide_hret) - geocentric pole tide height (pole_tide) - solid earth tide height (solid_earth_tide) - mean sea surface (mean_sea_surface_cnescls). m short 32767 N/A 0.001 N/A
surface_classification_flag Computed from a mask built with MODIS and GlobCover data, 0 = Open ocean; 1 = Land; 2 = Continental waters; 3 = Aquatic vegetation; 4 = Continental ice and snow; 5 = Floating ice; 6 = Salted basin. See TOPEX User Handbook. N/A byte 127 N/A 1 N/A
swh_20hz_c 20 Hz C-band MLE3 significant waveheight. Instrumental corrections are not required. m short 32767 N/A 0.001 N/A
swh_20hz_ku 20 Hz Ku-band MLE4 significant waveheight. Instrumental corrections are not required. m short 32767 N/A 0.001 N/A
swh_20hz_ku_mle3 20 Hz Ku-band MLE3 significant waveheight. Instrumental corrections are not required. m short 32767 N/A 0.001 N/A
swh_c 1 Hz C-band MLE3 significant waveheight. Instrumental corrections are not required. m short 32767 N/A 0.001 N/A
swh_c_qual Quality flag for 1 Hz C-band MLE3 significant waveheight. N/A byte 127 N/A 1 N/A
swh_ku 1 Hz Ku-band MLE4 significant waveheight. Instrumental corrections are not required. m short 32767 N/A 0.001 N/A
swh_ku_mle3 1 Hz Ku-band MLE3 significant waveheight. Instrumental corrections are not required. m short 32767 N/A 0.001 N/A
swh_ku_mle3_qual Quality flag for 1 Hz Ku-band MLE3 significant waveheight. N/A byte 127 N/A 1 N/A
swh_ku_qual Quality flag for 1 Hz Ku-band MLE4 significant waveheight. N/A byte 127 N/A 1 N/A
swh_model MFWAM global wave model significant waveheight. m short 32767 N/A 0.001 N/A
swh_numval_c Number of 20 hz C-band MLE3 significant waveheight measurements (swh_20hz_c) used to generate 1 Hz significant waveheight. count byte 127 0 to 20 1 N/A
swh_numval_ku Number of 20 Hz Ku-band MLE4 significant waveheight measurements (swh_20hz_ku) used to generate 1 Hz significant waveheight. count byte 127 0 to 20 1 N/A
swh_numval_ku_mle3 Number of 20 Hz Ku-band MLE3 significant waveheight measurements (swh_20hz_ku_mle3) used to generate 1 Hz significant waveheight. count byte 127 0 to 20 1 N/A
swh_rms_c RMS of 20 Hz C-band MLE3 significant waveheight measurements. Only valid 20 Hz measurements are used to compute this element. m short 32767 N/A 0.001 N/A
swh_rms_ku RMS of 20 Hz Ku-band MLE4 significant waveheight measurements. Only valid 20 Hz measurements are used to compute this element. m short 32767 N/A 0.001 N/A
swh_rms_ku_mle3 RMS of 20 Hz Ku-band MLE3 significant waveheight measurements. Only valid 20 Hz measurements are used to compute this element. m short 32767 N/A 0.001 N/A
swh_used_20hz_c Map of valid points from swh_20hz_c used to compute 1-Hz C-band MLE3 significant waveheight, swh_c. N/A byte 127 N/A 1 N/A
swh_used_20hz_ku Map of valid points from swh_20hz_ku used to compute 1-Hz Ku-band MLE4 significant waveheight, swh_ku. N/A byte 127 N/A 1 N/A
swh_used_20hz_ku_mle3 Map of valid points from swh_20hz_ku_mle3 used to compute 1-Hz Ku-band MLE3 significant waveheight, swh_ku_mle3. N/A byte 127 N/A 1 N/A
time [tai_utc_difference] is the difference between TAI and UTC reference time (seconds) for the first measurement of the data set. [leap_second] is the UTC time at which a leap second occurs in the data set, if any. After this UTC time, the tai_utc_difference is increased by 1 second. seconds since 2000-01-01 00:00:00.0 double N/A N/A 1 N/A
time_20hz [tai_utc_difference] is the difference between TAI and UTC reference time (seconds) for the first measurement of the data set. [leap_second] is the UTC time at which a leap second occurs in the data set, if any. After this UTC time, the tai_utc_difference is increased by 1 second. seconds since 2000-01-01 00:00:00.0 double N/A N/A 1 N/A
time_tai Time of measurement in seconds in the TAI time scale since 1 Jan 2000 00:00:00 TAI. This time scale contains no leap seconds. The difference (in seconds) with time in UTC is given by the attribute [time:tai_utc_difference]. seconds since 2000-01-01 00:00:00.0 double N/A N/A 1 N/A
wind_speed_alt Should not be used over land. Computed from MLE4 backscatter coefficient (sig0_ku) and significant waveheight (swh_ku). A bias of 2.69 dB is added to sig0_ku before computing wind speed with Collard Jason-1 wind speed algorithm. m/s short 32767 N/A 0.01 N/A
wind_speed_alt_mle3 Should not be used over land. Computed from MLE3 backscatter coefficient (sig0_ku_mle3) and significant waveheight (swh_ku_mle3). A bias of 2.69 dB is added to sig0_ku before computing wind speed with Collard Jason-1 wind speed algorithm. m/s short 32767 N/A 0.01 N/A
wind_speed_mod_u Computed at the altimeter time-tag from the interpolation of 2 meteorological fields that surround the altimeter time-tag. See TOPEX User Handbook. m/s short 32767 N/A 0.01 N/A
wind_speed_mod_v Computed at the altimeter time-tag from the interpolation of 2 meteorological fields that surround the altimeter time-tag. See TOPEX User Handbook. m/s short 32767 N/A 0.01 N/A
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