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Description

This dataset contains the Version 2.1 CYGNSS Level 2 Science Data Record which provides the time-tagged and geolocated average wind speed (m/s) and mean square slope (MSS) with 25x25 kilometer resolution from the Delay Doppler Mapping Instrument aboard the CYGNSS satellite constellation. This version supersedes Version 2.0. The reported sample locations are determined by the specular points corresponding to the Delay Doppler Maps (DDMs). A subset of DDM data used in the direct processing of the average wind speed and MSS is co-located inside of the Level 2 data files. Only one netCDF data file is produced each day (each file containing data from up to 8 unique CYGNSS spacecraft) with a latency of approximately 6 days (or better) from the last recorded measurement time. The Version 2.1 release represents the second science-quality release. Here is a summary of improvements that reflect the quality of the Version 2.1 data release: 1) revised Geophysical Model Functions (GMFs) for both Fully Developed Seas (FDS) and Young Seas with Limited Fetch conditions, to be consistent with the calibration changes made to the v2.1 Level 1 science data products.; 2) Revised covariance matrix between DDMA and LES versions of the FDS wind speed retrieval, used by the minimum variance estimator, resulting from changes made to the v2.1 Level 1 science data products; 3) Revised debiasing algorithm coefficients used by the FDS L2 retrieval algorithm, resulting from changes made to the v2.1 Level 2 science data products; 4) revised quality control (Q/C) flags related to the required level of consistency between DDMA and LES versions of the FDS wind speed retrieval (the errors in the two retrievals are now less correlated so larger discrepancies are allowed; if either retrieval is not available, the sample receives a fatal Q/C flag); 5) new Q/C flag related to the block type of the GPS satellite which provided the transmitted signal. Samples using block II-F signals receive a fatal Q/C flag due to the higher level of uncertainty in their radiated power; 6) revised wind speed uncertainty values as a function of RCG and wind speed, plus a new dependence of the uncertainty on GPS block type to reflect the higher uncertainty in GPS radiated power for block II-F satellites.

Product Summary

Platforms
CYGNSS
Instruments
DDMI
Spatial Extent

N: 40 S: -40 E: 180 W: -180

Spatial Resolution
25000 Meters x 25000 Meters
Geographic Region
GLOBAL ,
TROPICS
Coordinate System
CARTESIAN
Granule Spatial Representation
CARTESIAN
Temporal Extent
2017-03-18 to Present
Data Partner
Physical Oceanography Distributed Active Archive Center, Jet Propulsion Laboratory, NASA (NASA/JPL/PODAAC) ,
Cyclone Global Navigation Satellite System Mission, NASA Earth Science System Pathfinder, University of Michigan (NASA/ESSP/UMICH/CYGNSS)
Concept ID
C2251464495-POCLOUD
Data State
ACTIVE
Number of Files/Granules
3187
Processing Level
2
Published
Updated
Science Keywords
Radar Cross-Section ,
Surface Winds ,
Surface Winds ,
SIGMA NAUGHT

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

CYGNSS. (2017). CYGNSS Level 2 Science Data Record Version 2.1 [Data set]. NASA Physical Oceanography Distributed Active Archive Center. https://doi.org/10.5067/CYGNS-L2X21 Date Accessed: 2025-12-13

Documents

USER'S GUIDE

ALGORITHM THEORETICAL BASIS DOCUMENT (ATBD)

ANOMALIES

DATA CITATION GUIDELINES

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GENERAL DOCUMENTATION

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
antenna The CYGNSS nadir antenna that received the reflected GPS signal associated with the DDMs utilized to derive wind_speed. 0 = none 1 = zenith (never used) 2 = nadir_starboard 3 = nadir_port 1 byte -99 N/A 1
averaged_l1 There can be up to 4 L1 samples within the same second contributing to a 1Hz time averaged L1 samples. Variables that carry this dimension, but have less than 4 contibuting L1 samples will have the rest of the values set to a fill value. 1 int N/A N/A 1
azimuth_angle The mean of the orbit frame azimuth angles of the specular points of the DDMs that were utilized to derive wind_speed, degrees. degree float -9999 N/A 1
ddm The netCDF coordinate variable associated with variables that are dimensioned by the 4 DDMI reflectometry channels. It enumerates the zero-justified index range of DDM reflectometry channels. Ranges from 0 to 3. 1 int N/A N/A 1
ddm_channel A five element array, one per DDM. Contains the Level 1 netCDF reflectometry channel of the corresponding DDM. Can be utilized together with the ddm_sample_index, spacecraft_num and 'source' look up the corresponding Level 1 DDM data and metadata. 1 byte -99 N/A 1
ddm_les A five element array, one element per DDM. Contains the corresponding DDM leading edge slope value, unitless. 1 float -9999 N/A 1
ddm_nbrcs A five element array, one element per DDM. Contains the corresponding DDM normalized bistatic radar cross section value, unitless. 1 float -9999 N/A 1
ddm_obs_utilized_flag A five element array, one element per DDM. Flag is set to one if the corresponding DDM was utilized to produce wind_speed. 1 byte -99 N/A 1
ddm_sample_index A five element array, one per DDM. Contains the Level 1 netCDF sample index of the corresponding DDM. Can be utilized together with ddm_channel, spacecraft_num and 'source' to look up the corresponding Level 1 DDM data and metadata. 1 int -9999 N/A 1
ddm_source The source of the Level 0 DDM raw counts and metadata utilized to derive wind_speed. 0 = E2ES (CYGNSS end-to-end simulator) 1 = GPS signal simulator 2 = CYGNSS spacecraft 3 = Source Unknown 1 byte -99 N/A 1
fds_les_wind_speed The average surface wind speed of the 25 x 25 km cell centered on lat and lon derived only from the LES observable using the fully developed seas geophysical model function, m/s. Multiple DDMs are utilized to derive fds_les_wind_speed. The number of DDMs ranges from 1 to 5. m s-1 float -9999 N/A 1
fds_nbrcs_wind_speed The average surface wind speed of the 25 x 25 km cell centered on lat and lon derived only from the NBRCS observable using the fully developed seas geophysical model function, m/s. Multiple DDMs are utilized to derive fds_nbrcs_wind_speed. The number of DDMs ranges from 1 to 5. m s-1 float -9999 N/A 1
fds_sample_flags Set of status flags, set to 1 if condition is true. Flag bit masks: 1 = fatal_composite_wind_speed_flag, logical OR of fatal FDS flags (fatal_neg_wind_speed OR fatal_high_wind_speed OR fatal_retrieval_ambiguity OR fatal_low_range_corr_gain OR fatal_single_observable OR fatal_low_quality_gps_ant_knowledge) 2 = non_fatal_neg_wind_speed_flag, -5 < wind_speed < 0 m/s 4 = non_fatal_neg_fds_nbrcs_wind_speed, -5 < fds_nbrcs_wind_speed < 0 m/s 8 = non_fatal_neg_fds_les_wind_speed, -5 < fds_les_wind_speed < 0 m/s 16 = fatal_neg_wind_speed, wind_speed <= -5 m/s 32 = fatal_neg_fds_nbrcs_wind_speed, fds_nbrcs_wind_speed <= -5 m/s 64 = fatal_neg_fds_les_wind_speed, fds_les_wind_speed <= -5 m/s 128 = fatal_high_wind_speed, fatal_high_fds_nbrcs_wind_speed and fatal_high_fds_les_wind_speed are both one 256 = fatal_high_fds_nbrcs_wind_speed, nbrcs_mean corresponds to a wind speed > maximum FDS NBRCS lookup table wind speed at incidence_angle 512 = fatal_high_fds_les_wind_speed, les_mean corresponds to a wind speed > maximum FDS LES lookup table wind speed at incidence_angle 1024 = non_fatal_ascending, satellite is on the ascending node of the orbit (subsatellite point latitude is increasing) 2048 = fatal_retrieval_ambiguity, wind_speed was derived from both fds_nbrcs_wind_speed and fds_les_wind_speed AND the absolute value of the difference between fds_nbrcs_wind_speed and fds_les_wind_speed is > 10.0 m/s 4096 = fatal_single_observable, wind_speed was derived from a single observable, either fds_nbrcs_wind_speed or fds_les_wind_speed, but not both. 8182 = fatal_low_range_corr_gain, range_corr_gain < 1 16384 = fatal_low_quality_gps_ant_knowledge, The directional gain pattern of the GPS transmit antenna, and hence the value of its gain in the direction of the specular point, is less well known for block type II-F GPS satellites. This flag indicates that Level 1 calibration was based on a GPS antenna gain value with a higher than normal uncertainty. The increase in uncertainty at higher wind speeds is reflected in the 'wind_speed_uncertainty' data field. N/A short -9999 N/A 1
fresnel_coeff The square of the left hand circularly polarized Fresnel electromagnetic voltage reflection coefficient at 1575 MHz for a smooth ocean surface at lat, lon. See UM document 148-0361 for a description of the calculation of the Fresnel coefficient, unitless. 1 float -9999 N/A 1
incidence_angle The mean of the incidence angles of the specular points of the DDMs that were utilized to derive wind_speed, degrees. degree float -9999 N/A 1
lat The mean of the specular point latitudes of the DDMs that were utilized to derive wind_speed, degrees North. degrees_north float -9999 N/A 1
les_mean The mean of the DDM LES values that were utilized to derive wind_speed, unitless. 1 float -9999 N/A 1
lon The mean of the specular point longitudes of the DDMs that were utilized to derive wind_speed, degrees East. degrees_east float -9999 N/A 1
mean_square_slope The average MSS of the 25 x 25 km cell centered on lat and lon, unitless. 1 float -9999 N/A 1
mean_square_slope_uncertainty The uncertainty of mean_square_slope, unitless. 1 float -9999 N/A 1
nbrcs_mean The mean of the DDM NBRCS values that were utilized to derive wind_speed, unitless. 1 float -9999 N/A 1
num_ddms_utilized The number of DDMs averaged together to produce wind_speed. The number of DDMs utilized depends on the incidence angle. Ranges from 1 to 5. 1 byte -99 N/A 1
prn_code The PRN code of the GPS signal associated with the DDMs utilized to derive wind_speed. Ranges from 0 to 32. 0 = reflectometry channel idle. 1 to 32 represent a PRN code. 1 byte -99 N/A 1
range_corr_gain The mean of the RCGs of the DDMs that were utilized to produce wind_speed. Individual RCGs are equal to the receive antenna gain in the direction of the specular point multiplied by 1e27 divided by the square of the receiver to the specular point range and the square of the transmitter to specular point range. Units: 1e27 *dBi * m^-4 1e-27 dBi meter-4 float -9999 N/A 1
sample The netCDF coordinate variable associated with the sample dimension, which enumerates the zero-justified index range of the DDM time instants contained in the file. 1 int N/A N/A 1
sample_flags Set of flags indicating general conditions for the sample, set to 1 if condition is true. Flag bit masks: 1 = low_quality_gps_ant_knowledge, The directional gain pattern of the GPS transmit antenna, and hence the value of its gain in the direction of the specular point, is less well known for block type II-F GPS satellites. This flag indicates that Level 1 calibration was based on a GPS antenna gain value with a higher than normal uncertainty. The increase in uncertainty at higher wind speeds is reflected in the uncertainty data fields. N/A short -9999 N/A 1
sample_time The mean of ddm_timestamp_utc of the DDMs that were utilized to derive wind_speed. Note that the DDM sampling period is not synchronized with the UTC change of second so sample_time can occur at any time relative to the UTC change of second. seconds since 2019-01-03 00:00:00.999261476 double N/A N/A 1
sc_alt The mean of the satellite altitudes above the WGS-84 ellipsoid of the DDMs that were utilized to derive wind_speed, meters. meter int -9999 N/A 1
sc_lat The mean of the subsatellite point latitudes of the DDMs that were utilized to derive wind_speed, degrees North. degrees_north float -9999 N/A 1
sc_lon The mean of the subsatellite point longitudes of the DDMs that were utilized to derive wind_speed, degrees East. degrees_east float -9999 N/A 1
spacecraft_id The CCSDS spacecraft identifier: 0xF7 (247): CYGNSS 1 0xF9 (249): CYGNSS 2 0x2B ( 43): CYGNSS 3 0x2C ( 44): CYGNSS 4 0x2F ( 47): CYGNSS 5 0x36 ( 54): CYGNSS 6 0x37 ( 55): CYGNSS 7 0x49 ( 73): CYGNSS 8 0x00 ( 0): end to end simulator 0x0E ( 14): engineering model 0x0D ( 15): default 0xFF (255): unknown 1 short -9999 N/A 1
spacecraft_num The CYGNSS spacecraft number: Ranges from 1 through 8 and 99. 1 through 8 are on-orbit spacecraft. 99 is the CYGNSS end-to-end simulator. 1 byte -99 N/A 1
sum_neg_brcs_value_used_for_nbrcs_flags The number of DDMs utilized to produce wind_speed that used at least one negative BRCS bin value to calculate NBRCS. Ranges from 1 to 5. 1 byte -99 N/A 1
sv_num The GPS unique space vehicle number that transmitted prn_code 1 short -9999 N/A 1
wind_speed The average surface wind speed of the 25 x 25 km cell centered on lat and lon derived from both the NBRCS and the LES observables using the fully developed seas geophysical model function, m/s. Multiple DDMs are utilized to derive wind_speed. The number of utilized DDMs ranges from 1 to 5. m s-1 float -9999 N/A 1
wind_speed_uncertainty Standard deviation of the additive wind speed error in the minimum variance fully developed seas wind speed retrieval (dependent on the RCG of the specular point location, the block type of the GPS satellite, and the wind speed), in m/s. m s-1 float -9999 N/A 1
yslf_les_wind_speed The surface wind speed centered on lat and lon derived only from the LES observable using the young seas/limited fetch geophysical model function, m/s. Multiple DDMs are utilized to derive wind_speed. The number of utilized DDMs ranges from 1 to 5. m s-1 float -9999 N/A 1
yslf_les_wind_speed_uncertainty Standard deviation of the additive wind speed error in yslf_les_wind_speed (dependent on the RCG of the specular point location, the block type of the GPS satellite, and the wind speed), in m/s. m s-1 float -9999 N/A 1
yslf_nbrcs_wind_speed The surface wind speed centered on lat and lon derived only from the NBRCS observable using the young seas/limited fetch geophysical model function, m/s. Multiple DDMs are utilized to derive wind_speed. The number of utilized DDMs ranges from 1 to 5. m s-1 float -9999 N/A 1
yslf_nbrcs_wind_speed_uncertainty Standard deviation of the additive wind speed error in yslf_nbrcs_wind_speed (dependent on the RCG of the specular point location, the block type of the GPS satellite, and the wind speed), in m/s. m s-1 float -9999 N/A 1
yslf_sample_flags Set of status flags, set to 1 if condition is true. Flag bit masks: 1 = fatal_composite_yslf_wind_speed, logical OR of fatal YSLF flags (fatal_neg_yslf_wind_speed OR fatal_high_yslf_wind_speed OR fatal_yslf_retrieval_ambiguity OR fatal_low_range_corr_gain OR fatal_low_quality_gps_ant_knowledge) 2 = spare_3, always zero 4 = spare_4, always zero 8 = fatal_neg_yslf_wind_speed, non_fatal_neg_yslf_nbrcs_wind_speed and non-fatal_neg_yslf_les_wind_speed are both one 16 = non_fatal_neg_yslf_nbrcs_wind_speed, yslf_nbrcs_wind_speed <= -5 m/s 32 = non_fatal_neg_yslf_les_wind_speed, yslf_les_wind_speed <= -5 m/s 64 = spare_5, always zero 128 = fatal_high_yslf_wind_speed, either fatal_high_yslf_nbrcs_wind_speed or fatal_high_yslf_les_wind_speed is one (or both are one) 256 = fatal_high_yslf_nbrcs_wind_speed, nbrcs_mean corresponds to a YSLF wind speed >= 99.9 m/s 512 = fatal_high_yslf_les_wind_speed, les_mean corresponds to a YSLF wind speed >= 99.9 m/s 1024 = non_fatal_ascending, satellite is on the ascending node of the orbit (subsatellite point latitude is increasing) 2048 = spare_6, always zero 4096 = spare_7, always zero 8192 = fatal_low_yslf_range_corr_gain, range corrected gain of the DDM used for YSLF winds is < 1 16384 = fatal_low_quality_gps_ant_knowledge, The directional gain pattern of the GPS transmit antenna, and hence the value of its gain in the direction of the specular point, is less well known for block II-F GPS satellites. This flag indicates that Level 1 calibration was based on a GPS antenna gain value with a higher than normal uncertainty. The increase in uncertainty at higher wind speeds is reflected in the 'yslf_nbrcs_wind_speed_uncertainty' and 'yslf_les_wind_speed_uncertainty' data fields. N/A short -9999 N/A 1
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