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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
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: 2025-12-14

Documents

Variables

Variables are a set of physical properties whose values determine the characteristics or behavior of something. For example, temperature and pressure are variables of the atmosphere. Parameters and variables can be used interchangeably. Variable level attributes provide individual information for each variable.

The Name in this table is the variable name. Fill value indicates missing or undefined data points in a variable. Valid range is the range of values the variable can store. Scale factor is used to increase or decrease the size of an object and can be used to correct for distortion. For questions on a specific variable, please use the Earthdata Forum.

Name Description Units Data Type Fill Value Valid Range Scale Factor
agc_20hz_c 20 Hz C-band On-Board Attenuator Gain Control (AGC) as provided in the original SDR, which includes temperature corrections. dB short 32767 N/A 0.01
agc_20hz_ku 20 Hz Ku-band On-Board Attenuator Gain Control (AGC) as provided in the original SDR, which includes temperature corrections. dB short 32767 N/A 0.01
agc_c 1 Hz C-band On-Board Attenuator Gain Control (AGC) as provided in the original SDR, which includes temperature corrections. dB short 32767 N/A 0.01
agc_ku 1 Hz Ku-band On-Board Attenuator Gain Control (AGC) as provided in the original SDR, which includes temperature corrections. dB short 32767 N/A 0.01
agc_numval_c Number of 20 Hz C-band AGC measurements (agc_20hz_c) used to generate 1 Hz AGC measurement. count byte 127 0 to 20 1
agc_numval_ku Number of 20 Hz Ku-band AGC measurements (agc_20hz_ku) used to generate 1 Hz AGC measurement. count byte 127 0 to 20 1
agc_rms_c RMS of 20 Hz C-band AGC measurements. Only valid 20 Hz measurements are used to compute this element. dB short 32767 N/A 0.01
agc_rms_ku RMS of 20 Hz Ku-band AGC measurements. Only valid 20 Hz measurements are used to compute this element. dB short 32767 N/A 0.01
altitude Altitude of satellite above the reference ellipsoid (GSFC POD solution). m int 2147483647 N/A 0.0001
altitude_20hz Altitude of satellite above the reference ellipsoid (GSFC POD solution). m int 2147483647 N/A 0.0001
altitude_cnes Altitude of satellite above the reference ellipsoid. CNES POE solution, standard F. m int 2147483647 N/A 0.0001
altitude_rate_mean_sea_surface The reference surface for the orbit altitude rate is the combined MGDR ( OSUMSS95 / JGM-3/OSU91A ) mean sea surface/geoid surface. m/s short 32767 N/A 0.01
alt_echo_type The altimeter echo type is determined by testing the rms of the 20 Hz range measurements and the number of valid 20 Hz range measurements against thresholds. N/A byte 127 N/A 1
alt_state_flag_c_band Flag indicating the C-band bandwidth. N/A byte 127 N/A 1
alt_state_flag_c_band_status Flag indicating altimeter C-band status. N/A byte 127 N/A 1
alt_state_flag_ku_band_status Flag indicating altimeter Ku-band status. N/A byte 127 N/A 1
alt_state_flag_oper Flag indicating the operating altimeter. N/A byte 127 N/A 1
cg_to_altimeter_timevarying_offset Time varying CG correction to add to reported ranges. Experimental correction due to fuel consumption and motion of solar array. Not included in the reported net instrument range corrections and not applied to reported ranges. m short 32767 N/A 0.0001
composite_wet_tropo_gpd composite wet tropospheric correction derived from radiometer measurements and GNSS data (where radiometer data is missing). m short 32767 N/A 0.0001
dac Computed at the altimeter time-tag from the interpolation of 2 meteorological fields that surround the altimeter time-tag. See TOPEX User Handbook. m short 32767 N/A 0.0001
delta_ellipsoid_tp_wgs84 Height difference between TOPEX ellipsoid and WGS84 ellipsoid. To reference the provided mean sea surface and sea surface height anomaly to the TOPEX ellipsoid, subtract this value from provided mean sea surface and add this value to the sea surface height anomaly. m int 2147483647 N/A 0.0001
depth_or_elevation ocean depth/land elevation m int 2147483647 N/A 1
distance_to_coast Distance to coast. m int 2147483647 N/A 1
geoid Computed from the geoid model with a correction to refer the value to the mean tide system i.e. includes the permanent tide (zero frequency). See TOPEX User Handbook. m int 2147483647 N/A 0.0001
ice_flag The ice flag predicts ice based upon the wind speed (wind_speed_alt_mle3) and monthly climatological latitude extent of ice. N/A byte 127 N/A 1
internal_tide_hret Includes the M2, K1, S2, O1 contributions . See TOPEX User Handbook. m short 32767 N/A 0.0001
inv_bar_cor Computed at the altimeter time-tag from the interpolation of 2 meteorological fields that surround the altimeter time-tag. See TOPEX User Handbook. m short 32767 N/A 0.0001
iono_cor_alt_ku An ionospheric correction must be added (negative value) to the instrument range to correct for ionospheric delays of the radar pulse. A calibration bias of -0.06945 m has been added to (range_ku + sea_state_bias_ku) - (range_c + sea_state_bias_c) before computing this correction. m short 32767 N/A 0.0001
iono_cor_alt_ku_mle3 An ionospheric correction must be added (negative value) to the instrument range to correct for ionospheric delays of the radar pulse. A calibration bias of -0.06945 m has been added to (range_ku_mle3 + sea_state_bias_ku_mle3) - (range_c + sea_state_bias_c) before computing this correction. m short 32767 N/A 0.0001
iono_cor_gim_ku An ionosphere correction must be added (negative value) to the instrument range to correct for ionospheric delays of the radar pulse. This value is generated from Global Ionosphere Maps (GIM) and are only available from repeat cycle 48. m short 32767 N/A 0.0001
l2_record_counter This is the L2 record counter. Starting from 0 for each level 2 product. count int 2147483647 N/A 1
latitude Positive latitude is North latitude, negative latitude is South latitude. degrees_north int 2147483647 N/A 1.0E-6
latitude_20hz Positive latitude is North latitude, negative latitude is South latitude. degrees_north int 2147483647 N/A 1.0E-6
load_tide_fes This value has already been added to the corresponding ocean tide height value recorded in the product (ocean_tide_fes). See TOPEX User Handbook. m short 32767 N/A 0.0001
load_tide_got This value has already been added to the corresponding ocean tide height value recorded in the product (ocean_tide_got). See TOPEX User Handbook. m short 32767 N/A 0.0001
longitude East longitude relative to Greenwich meridian. degrees_east int 2147483647 N/A 1.0E-6
longitude_20hz East longitude relative to Greenwich meridian. degrees_east int 2147483647 N/A 1.0E-6
mean_dynamic_topography The mean dynamic topography is referenced to a 20 years mean. See TOPEX User Handbook. m int 2147483647 N/A 0.0001
mean_dynamic_topography_acc See TOPEX User Handbook. m int 2147483647 N/A 0.0001
mean_dynamic_topography_qual 0 = valid interpolation; 1 = failure of interpolation i.e. mean_dynamic_topography set to default value N/A byte 127 N/A 1
mean_sea_surface_cnescls The mean sea surface height is referenced to a 20 years mean. See TOPEX User Handbook. m int 2147483647 N/A 0.0001
mean_sea_surface_cnescls_acc See TOPEX User Handbook. m int 2147483647 N/A 0.0001
mean_sea_surface_cnescls_qual 0 = valid interpolation; 1 = failure of interpolation i.e. mean_sea_surface_cnescls set to default value N/A byte 127 N/A 1
mean_sea_surface_dtu The mean sea surface height is referenced to a 20 years mean. See TOPEX User Handbook. m int 2147483647 N/A 0.0001
mean_sea_surface_dtu_acc See TOPEX User Handbook. m int 2147483647 N/A 0.0001
mean_sea_surface_dtu_qual 0 = valid interpolation; 1 = failure of interpolation i.e. mean_sea_surface_dtu set to default value N/A byte 127 N/A 1
mean_wave_period_t02 t02 mean wave period s short 32767 N/A 0.01
meas_ind Used for all 20hz quantities. count byte N/A N/A 1
model_dry_tropo_cor_measurement_altitude Computed from 3d meteorological fields at measurement altitude, at the altimeter time-tag from the interpolation of 2 meteorological fields that surround the altimeter time-tag. A dry tropospheric correction must be added (negative value) to the instrument range to correct this range measurement for dry tropospheric range delays of the radar pulse. See TOPEX User Handbook. m short 32767 N/A 0.0001
model_dry_tropo_cor_zero_altitude Computed at mean sea level at the altimeter time-tag from the interpolation of 2 meteorological fields that surround the altimeter time-tag. A dry tropospheric correction must be added (negative value) to the instrument range to correct this range measurement for dry tropospheric range delays of the radar pulse. See TOPEX User Handbook. m short 32767 N/A 0.0001
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