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Description

This dataset contains the Version 1.0 CYGNSS Level 2 Climate 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. 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 2 months (or better) from the last recorded measurement time. The Version 1.0 CDR represents the first climate-quality release and is a collection of reanalysis products derived from the SDR v2.1 Level 1 data. Calibration accuracy and long term stability are improved relative to the SDR v2.1 using a new trackwise correction algorithm which constrains the average value of the L1 data using MERRA-2 reanalysis wind speeds. Details of the algorithm are provided in the Trackwise Corrected CDR Algorithm Theoretical Basis Document. CDR Level 2 and 3 products (ocean surface wind speed, mean square slope, and latent and sensible heat flux) are generated from the CDR L1 data using the v2.1 SDR data processing algorithms. These products also exhibit improved calibration accuracy and stability over SDR v2.1. Trackwise correction is applied to the two primary CYGNSS L1 science data products the normalized bistatic radar cross section (NBRCS) and the leading edge slope of the Doppler-integrated delay waveform (LES). The correction compensates for variations in the transmit power level of the GPS signals measured by the CYGNSS bistatic radar receivers. The SDR v2.1 L1 algorithm assumes a constant GPS transmit power and variations in it can be misinterpreted as variations in the L1 data and in subsequent L2 science data products derived from them. The GPS constellation consists of several different satellite models (a.k.a. block types) and the level of transmit power variation differs between them. The more recent Block IIF models (which account for ~37% of the GPS constellation) have significantly larger variations than the older models and, for this reason, they have been screened out and not used to produce SDR v2.1 L2 or L3 science data products. Trackwise correction eliminates the need for this screening so CDR L2 and L3 data products now include Block IIF samples. It should be noted that the trackwise correction algorithm cannot be successfully applied to all SDR v2.1 L1 data so there is also some loss of samples that were present in SDR v2.1. Overall, there is a significant increase in sampling and improvement in spatial coverage with the CDR products.

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 2021-02-28
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
C2036882048-POCLOUD
Data State
COMPLETE
Number of Files/Granules
1444
Processing Level
2
Published
Updated
Science Keywords
Surface Winds ,
Surface Winds

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. (2020). CYGNSS Level 2 Climate Data Record Version 1.0 [Data set]. NASA Physical Oceanography Distributed Active Archive Center. https://doi.org/10.5067/CYGNS-L2C10 Date Accessed: 2025-12-13

Documents

USER'S GUIDE

ALGORITHM THEORETICAL BASIS DOCUMENT (ATBD)

ANOMALIES

DATA CITATION GUIDELINES

GENERAL DOCUMENTATION

PUBLICATIONS

SHOWING 1 OF 1

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 Depending on the L1 sampling rate (1Hz to 4Hz), up to 4 DDMs can occur within the same second. An initial L2 processing stage averages these L1 values into a single per-second value. In turn, up to 5 of those one second averaged values can contribute to an L2 sample, yielding the possibility that up to 20 DDMs contribute to an L2 sample. The variables with this dimension captures the L1 sub-second values contributing to a given sample. If less than 4 DDMs are used in the intra-second average, the unused positions of such variables are 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 Wind retrievals are produced utilizing from one to five one second averaged DDMs. The values with this dimension are five element arrays which contain per-DDM values. The DDMs that were utilized for wind retrieval are indicated by the ddm_obs_utilized_flag array. If less than 5 DDMs are used in the average, the unused positions of such variables are set to a fill value. 1 int N/A N/A 1
ddm_averaged_l1_utilized_flag Each element is a flag set to one if the corresponding DDM was utilized to produce wind_speed. There can be up to 20 L1 DDMs used for a single L2 sample. Up to 4 samples that occur within the same second can be averaged together to form a one second averaged DDM and up to 5 one second averaged DDMs can contribute to an L2 sample. 1 byte -99 N/A 1
ddm_channel A five element array, one for each DDM used in the temporal average for the wind speed product. 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 for each DDM used in the temporal average for the wind speed product. Contains the corresponding DDM leading edge slope value, unitless. 1 float -9999 N/A 1
ddm_nbrcs A five element array, one for each DDM used in the temporal average for the wind speed product. Contains the corresponding DDM normalized bistatic radar cross section value, unitless. 1 float -9999 N/A 1
ddm_num_averaged_l1 A five element array, one for each DDM used in the temporal average for the wind speed product. Each value is the number of valid L1 samples averaged together to create a one Hz time averaged L1 sample. 1 byte -99 N/A 1
ddm_obs_utilized_flag A five element array, one for each DDM used in the temporal average for the wind speed product. Flag is set to one if the corresponding DDM was utilized to produce wind_speed. 1 byte -99 N/A 1
ddm_sample_index 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. There can be up to 20 L1 DDMs used for a single L2 sample. Up to 4 samples that occur within the same second can be averaged together to form a one second averaged DDM and up to 5 one second averaged DDMs can contribute to an L2 sample. All non-utilized values will be set to a fill value. 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) 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 > 2.5 m/s if wind_speed is < 6 m/s. If wind_speed is >= 6 m/s the absolute value of the difference between fds_nbrcs_wind_speed and fds_les_wind_speed is > 2.5*|wind_speed - 5|^0.5. 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 = spare_1, always zero 32768 = spare_2, always zero N/A int -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
merra2_wind_speed The average surface wind speed of the 25 x 25 km cell centered on lat and lon derived from the co-located MERRA-2 reference wind speed. See https://disc.gsfc.nasa.gov/datasets/M2I1NXASM_5.12.4/summary?keywords=%22MERRA-2%22 m s-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 = spare_0, always zero 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 2017-03-18 00:00:00.999261471 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 yslf_tw_error) 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 = spare_8, always zero 32768 = yslf_tw_error, If any of the following conditions are met the YSLF trackwise flag will be set: nbrcs_tw_outlier != 0 OR nbrcs_tw_r2 <= 0.7 OR RCG <= 20 OR ddm_nbrcs <= 8 OR nbrcs_tw_slope <= 0.5 OR nbrcs_tw_slope >= 1.5 OR |nbrcs_tw_yint - (c1*nbrcs_tw_slope + c0)| > 4 where c1 = -24.336 and c0 = 26.560 N/A int -9999 N/A 1
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