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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: 2026-06-04

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
model_wet_tropo_cor_zero_altitude Computed at mean sea level at the altimeter time-tag from the interpolation of 2 ERA meteorological fields that surround the altimeter time-tag. A wet tropospheric correction must be added (negative value) to the instrument range to correct this range measurement for wet tropospheric range delays of the radar pulse. See TOPEX User Handbook. m short 32767 N/A 0.0001 N/A
mqe_20hz_c Mean quadratic error from 20 Hz C-band MLE3 numerical retracking. count int 2147483647 N/A 0.0001 N/A
mqe_20hz_ku Mean quadratic error from 20 Hz Ku-band MLE4 numerical retracking. count int 2147483647 N/A 0.0001 N/A
mqe_20hz_ku_mle3 Mean quadratic error from 20 Hz Ku-band MLE3 numerical retracking. count int 2147483647 N/A 0.0001 N/A
net_instr_cor_range_c Sum of static CG offset (cg_to_altimeter_static_offset_mm), oscillator drift range correction (osc_drift_cor), C-band doppler correction (range_cor_doppler_c), tracking mode correction (value of 0 unless in coarse acquisition), C-band point target response centering prior to retracking, and correction for the impact of the point target response on the retracked C-band ranges (range_long_term_evolution_retracking_correction_c_mm + range_long_term_evolution_ptr_tracking_correction_c_mm). m int 2147483647 N/A 0.0001 N/A
net_instr_cor_range_ku Sum of static CG offset (cg_to_altimeter_static_offset_mm), oscillator drift range correction (osc_drift_cor), Ku-band doppler correction (range_cor_doppler_ku), tracking mode correction (value of 0 unless in coarse acquisition), Ku-band point target response centering prior to retracking, and correction for the impact of the point target response on the retracked Ku-band ranges (range_long_term_evolution_retracking_correction_ku_mm + range_long_term_evolution_ptr_tracking_correction_ku_mm). m int 2147483647 N/A 0.0001 N/A
net_instr_cor_range_ku_mle3 Sum of static CG offset (cg_to_altimeter_static_offset_mm), oscillator drift range correction (osc_drift_cor), Ku-band doppler correction (range_cor_doppler_ku), tracking mode correction (value of 0 unless in coarse acquisition), Ku-band point target response centering prior to retracking, and correction for the impact of the point target response on the retracked Ku-band ranges (range_long_term_evolution_retracking_correction_ku_mm + range_long_term_evolution_ptr_tracking_correction_ku_mm). m int 2147483647 N/A 0.0001 N/A
net_instr_cor_sig0_c PTR-based amplitude correction. dB short 32767 N/A 0.01 N/A
net_instr_cor_sig0_ku PTR-based amplitude correction. dB short 32767 N/A 0.01 N/A
net_instr_cor_sig0_ku_mle3 PTR-based amplitude correction. dB short 32767 N/A 0.01 N/A
num_iterations_c The number of iterations used to average the 20 Hz to 1 Hz C-band MLE3 measurements. count byte 127 N/A 1 N/A
num_iterations_ku The number of iterations used to average the 20 Hz to 1 Hz Ku-band MLE4 measurements. count byte 127 N/A 1 N/A
num_iterations_ku_mle3 The number of iterations used to average the 20 Hz to 1 Hz Ku-band MLE3 measurements. count byte 127 N/A 1 N/A
ocean_tide_eq This value has already been added to the two geocentric ocean tide height values recorded in the product (ocean_tide_fes and ocean_tide_got). The permanent tide (zero frequency) is not included in this parameter because it is included in the geoid and mean sea surface (geoid, mean_sea_surface). See TOPEX User Handbook. m short 32767 N/A 0.0001 N/A
ocean_tide_fes Includes the corresponding loading tide (load_tide_fes) and equilibrium long-period ocean tide height (ocean_tide_eq). The permanent tide (zero frequency) is not included in this parameter because it is included in the geoid and mean sea surface (geoid, mean_sea_surface). See TOPEX User Handbook. m int 2147483647 N/A 0.0001 N/A
ocean_tide_fes_qual 0 = valid interpolation; 1 = failure of interpolation i.e. ocean_tide_fes set to default value N/A byte 127 N/A 1 N/A
ocean_tide_got Includes the corresponding loading tide (load_tide_got) and equilibrium long-period ocean tide height (ocean_tide_eq). The permanent tide (zero frequency) is not included in this parameter because it is included in the geoid and mean sea surface (geoid, mean_sea_surface). See TOPEX User Handbook. m int 2147483647 N/A 0.0001 N/A
ocean_tide_got_qual 0 = valid interpolation; 1 = failure of interpolation i.e. ocean_tide_got set to default value N/A byte 127 N/A 1 N/A
ocean_tide_non_eq This parameter is computed as a correction to the parameter ocean_tide_eq. This value can be added to ocean_tide_eq (or ocean_tide_fes, ocean_tide_got) so that the resulting value models the total non equilibrium ocean tide height. See TOPEX User Handbook. m short 32767 N/A 0.0001 N/A
off_nadir_angle_wf_20hz_ku 20 Hz Ku-band MLE4 square of off nadir angle. degree^2 short 32767 N/A 0.0001 N/A
off_nadir_angle_wf_ku 1 Hz Ku-band MLE4 square of off nadir angle. degree^2 short 32767 N/A 0.0001 N/A
off_nadir_angle_wf_ku_qual Quality flag for 1 Hz Ku-band MLE4 square of off nadir angle measurement. N/A byte 127 N/A 1 N/A
off_nadir_angle_wf_ku_smoothed Smoothed mispointing derived from off_nadir_angle_wf_ku and used as input for Ku-band MLE3 retracking. degree^2 short 32767 N/A 0.0001 N/A
off_nadir_angle_wf_numval_ku Number of 20 Hz Ku-band MLE4 square of off nadir angle measurements (off_nadir_angle_wf_20hz_ku) used to generate 1 Hz measurement. count byte 127 0 to 20 1 N/A
off_nadir_angle_wf_rms_ku RMS of 20 Hz Ku-band MLE4 square of off nadir angle measurements. Only valid 20 Hz measurements are used to compute this element. degree^2 short 32767 N/A 0.0001 N/A
off_nadir_angle_wf_used_20hz_ku Map of valid points from off_nadir_angle_20hz_ku used to compute 1-Hz Ku-band MLE4 square of off nadir angle, off_nadir_angle_wf_ku. N/A byte 127 N/A 1 N/A
osc_drift_cor Correction to Ku- and C-band ranges from drift in oscillator m int 2147483647 N/A 0.0001 N/A
pole_tide Adopts Ries and Desai [2017] model for mean pole location. Xp = 55.0 + 1.677*DT, Yp = 320.5 + 3.460*DT in milliarcseconds with DT = years since 2000.0. m short 32767 N/A 0.0001 N/A
rad_atm_cor_sig0_c Value has been added to computed backscatter coefficient to generate reported backscatter. dB short 32767 0 to 32766 0.001 N/A
rad_atm_cor_sig0_c_qual Quality flag for radiometer two-way atmospheric correction to C band backscatter coefficient. N/A byte 127 0 to 1 1 N/A
rad_atm_cor_sig0_ku Value has been added to computed backscatter coefficient to generate reported backscatter. dB short 32767 0 to 32766 0.001 N/A
rad_atm_cor_sig0_ku_qual Quality flag for radiometer two-way atmospheric correction to Ku band backscatter coefficient. N/A byte 127 0 to 1 1 N/A
rad_cloud_liquid_water Integrated cloud liquid water content. kg/m^2 short 32767 0 to 32766 0.01 N/A
rad_cloud_liquid_water_qual Quality flag for radiometer cloud liquid water content. N/A byte 127 0 to 1 1 N/A
rad_distance_to_land Shortest distance between main beam measurement and land. m int 2147483647 0 to 2147483646 100 N/A
rad_land_frac_18 Fraction of land within the 18 GHz main beam. Value is from 0 to 1. 1 short 32767 0 to 10000 0.0001 N/A
rad_land_frac_21 Fraction of land within the 21 GHz main beam. Value is from 0 to 1. 1 short 32767 0 to 10000 0.0001 N/A
rad_land_frac_37 Fraction of land within the 37 GHz main beam. Value is from 0 to 1. 1 short 32767 0 to 10000 0.0001 N/A
rad_rain_flag Flag indicating if radiometer measurement is invalid due to rain contamination. N/A byte 127 0 to 1 1 N/A
rad_sea_ice_flag Flag indicating if radiometer measurement is invalid due to sea ice contamination. N/A byte 127 0 to 1 1 N/A
rad_surface_type_flag Flag indicating the validity and type of processing applied to generate the wet troposphere correction (rad_wet_tropo_cor). A value of 0 indicates that open ocean processing is used, a value of 1 indicates coastal processing, and a value of 2 indicates that rad_wet_tropo_cor is invalid due to land contamination. N/A byte 127 0 to 2 1 N/A
rad_ta_18 Antenna temperature measurement at 18 GHz. K int 2147483647 0 to 36000 0.01 N/A
rad_ta_18_qual Quality flag for 18 GHz antenna temperature. N/A byte 127 0 to 1 1 N/A
rad_ta_21 Antenna temperature measurement at 21 GHz. K int 2147483647 0 to 36000 0.01 N/A
rad_ta_21_qual Quality flag for 21 GHz antenna temperature. N/A byte 127 0 to 1 1 N/A
rad_ta_37 Antenna temperature measurement at 37 GHz. K int 2147483647 0 to 36000 0.01 N/A
rad_ta_37_qual Quality flag for 37 GHz antenna temperature. N/A byte 127 0 to 1 1 N/A
rad_tb_18 Equalized brightness temperature measurement at 18 GHz. Value is smoothed (along-track averaging has been performed). K int 2147483647 N/A 0.01 N/A
rad_tb_18_qual Quality flag for 18 GHz equalized brightness temperature. N/A byte 127 0 to 1 1 N/A
rad_tb_21 Equalized brightness temperature measurement at 21 GHz. Value is smoothed (along-track averaging has been performed). K int 2147483647 N/A 0.01 N/A
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