Skip to main content

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_2.0

https://podaac.jpl.nasa.gov/dataset/SWOT_L2_NALT_GDR_GDR_2.0

https://podaac.jpl.nasa.gov/dataset/SWOT_L2_NALT_GDR_SGDR_2.0

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
C2799438313-POCLOUD
Data State
SUPERSEDED
Number of Files/Granules
62627
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. (2024). SWOT Level 2 Nadir Altimeter Geophysical Data Record with Waveforms Version 2.0 [Data set]. NASA Physical Oceanography Distributed Active Archive Center. https://doi.org/10.5067/SWOT-NALT-GDR-2.0 Date Accessed: 2026-06-03

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/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 shall not be used with the mean sea surface (mean_sea_surface_cnescls or mean_sea_surface_dtu) provided in the product. 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 +0.06 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/agc AGC is corrected for instrumental errors due to the imperfections of the on-board attenuators dB short 32767 N/A 0.01 N/A
/data_20/c/agc_cor Comes from AGC static characterization, and added to on-board AGC to obtain applied AGC dB short 32767 N/A 0.01 N/A
/data_20/c/amplitude_ice2 C band amplitude (ice-2 retracking) [FFT power unit] count int 2147483647 N/A 0.0001 N/A
/data_20/c/amplitude_ocean C band amplitude (ocean retracking) [FFT power unit] count int 2147483647 N/A 0.0001 N/A
/data_20/c/amplitude_ocog C band amplitude (OCOG retracking) [FFT power unit] count int 2147483647 N/A 0.0001 N/A
/data_20/c/epoch_ice2 C band epoch (ice-2 retracking) s int 2147483647 N/A 1.0E-15 N/A
/data_20/c/epoch_ocean C band epoch (ocean retracking) s int 2147483647 N/A 1.0E-15 N/A
/data_20/c/epoch_ocog C band epoch (OCOG retracking) s int 2147483647 N/A 1.0E-15 N/A
/data_20/c/ice2_qual ice-2 retracking quality flag N/A byte 127 N/A 1 N/A
/data_20/c/mean_amplitude_ice2 C band mean amplitude (ice-2 retracking) [FFT power unit] count int 2147483647 N/A 0.0001 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/noise_floor_ice2 C band thermal noise (ice-2 retracking) [FFT power unit] count int 2147483647 N/A 1.0E-6 N/A
/data_20/c/noise_floor_ocean C band thermal noise (ocean retracking) [FFT power unit] count int 2147483647 N/A 1.0E-6 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/power_waveform Waveforms are corrected for the Low Pass Filter effects count 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
/data_20/c/range_ocean All instrumental corrections included, i.e. 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), modeled instrumental errors correction (/data_01/c/range_cor_ocean_model_instr) and system bias m int 2147483647 N/A 0.0001 800000
/data_20/c/range_ocean_compression_qual Map of valid points used to compute the 1 Hz C band altimeter range N/A byte 127 N/A 1 N/A
/data_20/c/range_ocog 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
/data_20/c/sig0_ice2 AGC instrumental errors correction and internal calibration correction (/data_01/c/sig0_cor_calibration) included dB short 32767 N/A 0.01 N/A
/data_20/c/sig0_leading_edge_ice2 AGC instrumental errors correction and internal calibration correction (/data_01/c/sig0_cor_calibration) included dB short 32767 N/A 0.01 N/A
/data_20/c/sig0_ocean All instrumental corrections included, excepted the system bias, i.e. AGC instrumental errors correction, internal calibration correction (/data_01/c/sig0_cor_calibration), modeled instrumental errors correction (/data_01/c/sig0_cor_ocean_model_instr) and atmospheric attenuation (sig0_cor_atm) dB short 32767 N/A 0.01 N/A
/data_20/c/sig0_ocean_compression_qual Map of valid points used to compute the 1 Hz C band backscatter coefficient N/A byte 127 N/A 1 N/A
/data_20/c/sig0_ocog AGC instrumental errors correction and internal calibration correction (/data_01/c/sig0_cor_calibration) included dB short 32767 N/A 0.01 N/A
/data_20/c/sig0_scaling_factor This scaling factor represents the backscatter coefficient for a C band waveform amplitude equal to 1. It is a raw value accounting for AGC 20 Hz correction and internal calibration correction. All other correction are not applied (ie atmospheric attenuation, modeled instrumental errors correction and system bias) dB int 2147483647 N/A 0.01 N/A
/data_20/c/sigmac_ocean The width of the leading edge corresponds to the so-called composite sigma (SigmaC) s int 2147483647 N/A 1.0E-15 N/A
/data_20/c/sigmal_ice2 The width of the leading edge corresponds to the so-called composite sigma (SigmaL) m short 32767 N/A 0.001 N/A
/data_20/c/slope1_ice2 20 Hz slope of the first part of the logarithm of the C band trailing edge (ice-2 retracking) s-1 int 2147483647 N/A 1 N/A
/data_20/c/slope2_ice2 20 Hz slope of the second part of the logarithm of the C band trailing edge (ice-2 retracking) s-1 int 2147483647 N/A 1 N/A
/data_20/c/swh_ocean All instrumental corrections included, i.e. modeled instrumental errors correction (/data_01/c/swh_cor_ocean_model_instr) and system bias m short 32767 N/A 0.001 N/A
/data_20/c/swh_ocean_compression_qual Map of valid points used to compute the 1 Hz C band significant waveheight N/A byte 127 N/A 1 N/A
You're viewing 250 of 342