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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_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
Projects
SWOT
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SUPERSEDED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_20/ku/sig0_adaptive_compression_qual Map of valid points used to compute the 1 Hz Ku band backscatter coefficient N/A byte 127 N/A 1 N/A
/data_20/ku/sig0_ice2 AGC instrumental errors correction and internal calibration correction (/data_01/ku/sig0_cor_calibration) included dB short 32767 N/A 0.01 N/A
/data_20/ku/sig0_leading_edge_ice2 AGC instrumental errors correction and internal calibration correction (/data_01/ku/sig0_cor_calibration) included dB short 32767 N/A 0.01 N/A
/data_20/ku/sig0_ocean All instrumental corrections included, excepted the system bias, i.e. AGC instrumental errors correction, internal calibration correction (/data_01/ku/sig0_cor_calibration), modeled instrumental errors correction (/data_01/ku/sig0_cor_ocean_model_instr) and atmospheric attenuation (sig0_cor_atm) dB short 32767 N/A 0.01 N/A
/data_20/ku/sig0_ocean_compression_qual Map of valid points used to compute the 1 Hz Ku band backscatter coefficient N/A byte 127 N/A 1 N/A
/data_20/ku/sig0_ocean_mle3 All instrumental corrections included, excepted the system bias, i.e. AGC instrumental errors correction, internal calibration correction (/data_01/ku/sig0_cor_calibration), modeled instrumental errors correction (/data_01/ku/sig0_cor_ocean_mle3_model_instr) and atmospheric attenuation (sig0_cor_atm) dB short 32767 N/A 0.01 N/A
/data_20/ku/sig0_ocean_mle3_compression_qual Map of valid points used to compute the 1 Hz Ku band backscatter coefficient N/A byte 127 N/A 1 N/A
/data_20/ku/sig0_ocog AGC instrumental errors correction and internal calibration correction (/data_01/ku/sig0_cor_calibration) included dB short 32767 N/A 0.01 N/A
/data_20/ku/sig0_scaling_factor This scaling factor represents the backscatter coefficient for a Ku 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/ku/sig0_seaice AGC instrumental errors correction and internal calibration correction (/data_01/ku/sig0_cor_calibration) included dB short 32767 N/A 0.01 N/A
/data_20/ku/sig0_tfmra AGC instrumental errors correction and internal calibration correction (/data_01/ku/sig0_cor_calibration) included dB short 32767 N/A 0.01 N/A
/data_20/ku/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/ku/sigmac_ocean_mle3 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/ku/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/ku/slope1_ice2 20 Hz slope of the first part of the logarithm of the Ku band trailing edge (ice-2 retracking) s-1 int 2147483647 N/A 1 N/A
/data_20/ku/slope2_ice2 20 Hz slope of the second part of the logarithm of the Ku band trailing edge (ice-2 retracking) s-1 int 2147483647 N/A 1 N/A
/data_20/ku/slope_ice2 20 Hz Ku band slope of the logarithm of the trailing edge for mispointing (ice-2 retracking) s-1 int 2147483647 N/A 1 N/A
/data_20/ku/swh_adaptive No correction applied m short 32767 N/A 0.001 N/A
/data_20/ku/swh_adaptive_compression_qual Map of valid points used to compute the 1 Hz Ku band significant waveheight N/A byte 127 N/A 1 N/A
/data_20/ku/swh_ocean All instrumental corrections included, i.e. modeled instrumental errors correction (/data_01/ku/swh_cor_ocean_model_instr) and system bias m short 32767 N/A 0.001 N/A
/data_20/ku/swh_ocean_compression_qual Map of valid points used to compute the 1 Hz Ku band significant waveheight N/A byte 127 N/A 1 N/A
/data_20/ku/swh_ocean_mle3 All instrumental corrections included, i.e. modeled instrumental errors correction (/data_01/ku/swh_cor_ocean_mle3_model_instr) and system bias m short 32767 N/A 0.001 N/A
/data_20/ku/swh_ocean_mle3_compression_qual Map of valid points used to compute the 1 Hz Ku band significant waveheight N/A byte 127 N/A 1 N/A
/data_20/ku/tfmra_qual TFMRA retracking quality flag N/A byte 127 N/A 1 N/A
/data_20/ku/tracker_range_calibrated Ku band operating tracker (’Diode+DEM’ or ’Median’ or ’Split-Gate’ tracker). This includes the Distance antenna-COG (/data_01/range_cor_cog), USO drift correction (/data_01/range_cor_uso) and internal path correction (/data_01/ku/range_cor_internal_path). But not the Doppler correction (/data_01/ku/range_cor_doppler), modeled instrumental errors correction (/data_01/ku/range_cor_ocean_model_instr) and system bias m int 2147483647 N/A 0.0001 800000
/data_20/ku/tracker_range_diode 20 Hz Ku band tracker range from Diode+DEM m int 2147483647 N/A 0.0001 800000
/data_20/ku/wvf_main_class Waveform classification : main class selected by classification neural network trained on shape features of the waveforms N/A byte 127 N/A 1 N/A
/data_20/ku/wvf_main_class_score Waveform classification : probability associated to the main class (between 0 and 100, 100=strongest probability) N/A short 32767 N/A 0.01 N/A
/data_20/ku/wvf_second_class Waveform classification : second class selected by classification neural network trained on shape features of the waveforms N/A byte 127 N/A 1 N/A
/data_20/ku/wvf_second_class_score Waveform classification : probability associated to the second class (between 0 and 100, 100=strongest probability) N/A short 32767 N/A 0.01 N/A
/data_20/latitude Positive latitude is North latitude, negative latitude is South latitude. See SWOT Nadir Altimeter User Handbook degrees_north int 2147483647 N/A 1.0E-6 N/A
/data_20/longitude East longitude relative to Greenwich meridian. See SWOT Nadir Altimeter User Handbook degrees_east int 2147483647 N/A 1.0E-6 N/A
/data_20/meteo_measurement_altitude_interp_qual 0 = interpolation from 4 points; 1 = interpolation from less than 4 points N/A byte 127 N/A 1 N/A
/data_20/model_dry_tropo_cor_measurement_altitude Computed at coarse DEM altitude (for O&amp;IGDR) or precise measurement altitude (for GDR) 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 SWOT Nadir Altimeter User Handbook m short 32767 N/A 0.0001 N/A
/data_20/model_wet_tropo_cor_measurement_altitude Computed at coarse DEM altitude (for O&amp;IGDR) or precise measurement altitude (for GDR) at the altimeter time-tag from the interpolation of 2 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 SWOT Nadir Altimeter User Handbook m short 32767 N/A 0.0001 N/A
/data_20/surface_classification_flag Computed from a mask built with MODIS and GlobCover data N/A byte 127 N/A 1 N/A
/data_20/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_20/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_20/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_20/tracker_range_counter Tracker range counter with a resolution of 3.125/64 ns count int 2147483647 N/A 1 2147483648
/data_20/tracker_range_rate_counter Tracker range rate counter with a resolution of 3.125/1024 ns count short 32767 N/A 1 N/A
samples Set to be compliant with the CF-1.7 convention count byte N/A N/A 1 N/A
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