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Description

The SWOT Level 2 Nadir Altimeter Geophysical Data Record (GDR) with Waveforms dataset produced by the Surface Water and Ocean Topography (SWOT) mission provides sea surface height, significant wave height and wind speed measurements from the Poseidon-3C nadir altimeter, a Jason-class dual frequency (Ku/C) altimeter. SWOT is a joint mission between NASA and CNES that launched on December 16, 2022. It aims to measure ocean surface topography with unprecedented resolution and accuracy, as well as map inland water bodies globally. The GDR dataset consists of discrete measurements for each half orbit along the ground track with sampling resolutions of approximately 6-km and 300-m at 1Hz and 20Hz, respectively. The data were processed using restituted auxiliary data and the Precise Orbit Ephemeris (POE). The data are available with latency of < 90 days and distributed in netCDF-4 file format.

This collection is the parent collection to the following sub-collections:

https://podaac.jpl.nasa.gov/dataset/SWOT_L2_NALT_GDR_SSHA_D

https://podaac.jpl.nasa.gov/dataset/SWOT_L2_NALT_GDR_GDR_D

https://podaac.jpl.nasa.gov/dataset/SWOT_L2_NALT_GDR_SGDR_D

Product Summary

Platforms
SWOT
Instruments
Jason-class Altimeter ,
AMR
Spatial Extent

N: 77.6 S: -77.6 E: 180 W: -180

Location
GLOBAL
Coordinate System
CARTESIAN
Granule Spatial Representation
CARTESIAN
Temporal Extent
2022-12-16
Data Partner
Physical Oceanography Distributed Active Archive Center, Jet Propulsion Laboratory, NASA (NASA/JPL/PODAAC)
Concept ID
C3317113871-POCLOUD
Data State
ACTIVE
Number of Files/Granules
95682
Processing Level
2
Published
Updated
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

SWOT. (2025). SWOT Level 2 Nadir Altimeter Geophysical Data Record with Waveforms [Data set]. NASA Physical Oceanography Distributed Active Archive Center. https://doi.org/10.5067/SWOT-NALT-GDR-D Date Accessed: 2026-06-01

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
/data_01/rad_side_1_sea_ice_flag See SWOT Nadir Altimeter User Handbook N/A byte 127 N/A 1 N/A
/data_01/rad_side_1_surface_type_flag radiometer surface type from first radiometer N/A byte 127 N/A 1 N/A
/data_01/rad_side_2_distance_to_land Shortest distance between nadir sub-satellite point and land m int 2147483647 N/A 1 N/A
/data_01/rad_side_2_land_frac_187 ratio between 0 and 1 1 short 32767 N/A 0.01 N/A
/data_01/rad_side_2_land_frac_238 ratio between 0 and 1 1 short 32767 N/A 0.01 N/A
/data_01/rad_side_2_land_frac_340 ratio between 0 and 1 1 short 32767 N/A 0.01 N/A
/data_01/rad_side_2_rain_flag See SWOT Nadir Altimeter User Handbook N/A byte 127 N/A 1 N/A
/data_01/rad_side_2_sea_ice_flag See SWOT Nadir Altimeter User Handbook N/A byte 127 N/A 1 N/A
/data_01/rad_side_2_surface_type_flag radiometer surface type from second radiometer N/A byte 127 N/A 1 N/A
/data_01/rad_tb_187 Brightness temperatures are along-track averaged K int 2147483647 N/A 0.01 N/A
/data_01/rad_tb_187_qual quality flag for 1 Hz radiometer data: 18.7 GHz brightness temperature N/A byte 127 N/A 1 N/A
/data_01/rad_tb_238 Brightness temperatures are along-track averaged K int 2147483647 N/A 0.01 N/A
/data_01/rad_tb_238_qual quality flag for 1 Hz radiometer data: 23.8 GHz brightness temperature N/A byte 127 N/A 1 N/A
/data_01/rad_tb_340 Brightness temperatures are along-track averaged K int 2147483647 N/A 0.01 N/A
/data_01/rad_tb_340_qual quality flag for 1 Hz radiometer data: 34 GHz brightness temperature N/A byte 127 N/A 1 N/A
/data_01/rad_tmb_187 Brightness temperatures are unsmoothed (along-track averaging has not been performed on the brightness temperatures) K int 2147483647 N/A 0.01 N/A
/data_01/rad_tmb_238 Brightness temperatures are unsmoothed (along-track averaging has not been performed on the brightness temperatures) K int 2147483647 N/A 0.01 N/A
/data_01/rad_tmb_340 Brightness temperatures are unsmoothed (along-track averaging has not been performed on the brightness temperatures) K int 2147483647 N/A 0.01 N/A
/data_01/rad_water_vapor Should not be used over land kg/m^2 short 32767 N/A 0.1 N/A
/data_01/rad_wet_tropo_cor 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 m short 32767 N/A 0.0001 N/A
/data_01/rad_wet_tropo_cor_interp_qual See SWOT Nadir Altimeter User Handbook N/A byte 127 N/A 1 N/A
/data_01/rad_wind_speed Should not be used over land. See SWOT Nadir Altimeter User Handbook m/s short 32767 N/A 0.01 N/A
/data_01/rain_flag See SWOT Nadir Altimeter User Handbook N/A byte 127 N/A 1 N/A
/data_01/rain_rate See SWOT Nadir Altimeter User Handbook mm/h short 32767 N/A 0.01 N/A
/data_01/sea_ice_concentration percentage between 0 and 100 1 short 32767 N/A 0.01 N/A
/data_01/sea_ice_concentration_interp_qual 0 = interpolation from 4 points; 1 = interpolation from less than 4 points N/A byte 127 N/A 1 N/A
/data_01/sig0_cor_atm_source Flag indicating whether the radiometer data or the climatological values from meteorological model (ECMWF backup solution) have been used to compute the atmospheric sigma0 correction N/A byte 127 N/A 1 N/A
/data_01/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 SWOT Nadir Altimeter User Handbook m short 32767 N/A 0.0001 N/A
/data_01/sst sea surface temperature K short 32767 N/A 0.01 N/A
/data_01/surface_classification_flag Computed from a mask built with MODIS and GlobCover data N/A byte 127 N/A 1 N/A
/data_01/surface_slope_cor The surface slope correction model aims to improve the accuracy of mean sea surface topography models as well as marine gravity models. See SWOT Nadir Altimeter User Handbook m int 2147483647 N/A 0.0001 N/A
/data_01/time Time of measurement in seconds in the UTC time scale since 1 Jan 2000 00:00:00 UTC. [tai_utc_difference] is the difference between TAI and UTC reference time (seconds) for the first measurement of the data set. If a leap second occurs within the data set, the attribute [leap_second] is set to the UTC time at which the leap second occurs seconds since 2000-01-01 00:00:00.0 double N/A N/A 1 N/A
/data_01/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 1.844674407371E+19 N/A 1 N/A
/data_01/wave_model_interp_qual 0 = interpolation from 4 points; 1 = interpolation from less than 4 points N/A byte 127 N/A 1 N/A
/data_01/wave_model_map_availability_flag Possible values are: 0 meaning ’2 maps, nominal’ (three hours apart), 1 meaning ’2 maps, degraded’ (more than three hours apart), 2 meaning ’1 map, closest map used’, 3 meaning ’no valid map’ N/A byte 127 N/A 1 N/A
/data_01/wind_speed_alt Should not be used over land. See SWOT Nadir Altimeter User Handbook. A calibration bias of +0.39 dB has been added to the Ku band backscatter coefficient (/data_01/ku/sig0_ocean) before computing the wind speed m/s short 32767 N/A 0.01 N/A
/data_01/wind_speed_alt_adaptive Should not be used over land. See SWOT Nadir Altimeter User Handbook. A calibration bias of +0.08 dB has been added to the Ku band backscatter coefficient (/data_01/ku/sig0_adaptive) before computing the wind speed m/s short 32767 N/A 0.01 N/A
/data_01/wind_speed_alt_mle3 Should not be used over land. See SWOT Nadir Altimeter User Handbook. A calibration bias of +0.109 dB has been added to the Ku band backscatter coefficient (/data_01/ku/sig0_ocean_mle3) before computing the wind speed m/s short 32767 N/A 0.01 N/A
/data_01/wind_speed_mod_u Computed at the altimeter time-tag from the interpolation of 2 meteorological fields that surround the altimeter time-tag. See SWOT Nadir Altimeter User Handbook m/s short 32767 N/A 0.01 N/A
/data_01/wind_speed_mod_v Computed at the altimeter time-tag from the interpolation of 2 meteorological fields that surround the altimeter time-tag. See SWOT Nadir Altimeter User Handbook m/s short 32767 N/A 0.01 N/A
/data_20/altitude Altitude of satellite above the reference ellipsoid m int 2147483647 N/A 0.0001 800000
/data_20/alt_state_acq_mode_flag 8 = autonomous acquisition / tracking, 9 = autonomous DIODE acquisition / tracking, 10 = DIODE + Digital Elevation Model tracking N/A byte 127 N/A 1 N/A
/data_20/alt_state_track_trans_flag 20 Hz altimeter state flag: tracking automatic transition N/A byte 127 N/A 1 N/A
/data_20/angle_of_approach_to_coast Angle of approach to the closest coast. 0 is parallel to the coast with the land on the right. Positive values indicate the satellite is approaching the land. Negative values indicate the satellite is leaving the land. Values close to +/-180 degrees have the land on the left degrees short 32767 N/A 0.01 N/A
/data_20/c/ice2_qual ice-2 retracking quality flag N/A byte 127 N/A 1 N/A
/data_20/c/mqe_ice2 Mean Quadratic Error between the waveforms samples and the corresponding model samples built from the ice-2 retracking outputs 1 int 2147483647 N/A 1.0E-5 N/A
/data_20/c/mqe_ocean Mean Quadratic Error between the waveforms samples and the corresponding model samples built from the ocean retracking outputs 1 short 32767 N/A 0.0001 N/A
/data_20/c/num_iterations_ocean 20 Hz number of iterations of the ocean retracking in C band count byte 127 N/A 1 N/A
/data_20/c/peakiness 20 Hz peakiness on C band waveforms 1 int 2147483647 N/A 0.001 N/A
/data_20/c/range_ice2 Distance antenna-COG (/data_01/range_cor_cog), USO drift correction (/data_01/range_cor_uso), internal path correction (/data_01/c/range_cor_internal_path), Doppler correction (/data_01/c/range_cor_doppler) and system bias included m int 2147483647 N/A 0.0001 800000
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