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Description

This Level 1 (L1) dataset contains the Version 1.0 Climate Data Record (CDR) of the geo-located Delay Doppler Maps (DDMs) calibrated into Power Received (Watts) and Bistatic Radar Cross Section (BRCS) expressed in units of m2 from the Delay Doppler Mapping Instrument aboard the CYGNSS satellite constellation. Other useful scientific and engineering measurement parameters include the DDM of Normalized Bistatic Radar Cross Section (NBRCS), the Delay Doppler Map Average (DDMA) of the NBRCS near the specular reflection point, and the Leading Edge Slope (LES) of the integrated delay waveform. The L1 dataset contains a number of other engineering and science measurement parameters, including sets of quality flags/indicators, error estimates, and bias estimates as well as a variety of orbital, spacecraft/sensor health, timekeeping, and geolocation parameters. At most, 8 netCDF data files (each file corresponding to a unique spacecraft in the CYGNSS constellation) are provided each day; under nominal conditions, there are typically 6-8 spacecraft retrieving data each day, but this can be maximized to 8 spacecraft under special circumstances in which higher than normal retrieval frequency is needed (i.e., during tropical storms and or hurricanes). Latency is approximately 2 months, depending on the availability of the MERRA wind speed reanalysis. The Version 1.0 CDR represents the first climate-quality release and is a collection of reanalysis products derived from the 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 provide in the Trackwise Corrected CDR Algorithm Theoretical Basis Document. The CDR exhibits improved calibration accuracy and stability over 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. By comparison, the v2.1 SDR 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 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 v2.1 SDR L1 data, so there is also some loss of samples that were present in 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
Location
GLOBAL ,
TROPICS
Coordinate System
CARTESIAN
Granule Spatial Representation
CARTESIAN
Temporal Extent
2017-03-18 to 2021-03-01
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
C1996881862-POCLOUD
Data State
COMPLETE
Number of Files/Granules
10918
Processing Level
1
Published
Updated
Science Keywords
Radar Cross-Section ,
Radar Reflectivity

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 1 Climate Data Record Version 1.0 [Data set]. NASA Physical Oceanography Distributed Active Archive Center. https://doi.org/10.5067/CYGNS-L1C10 Date Accessed: 2026-06-01

Documents

USER'S GUIDE

ALGORITHM THEORETICAL BASIS DOCUMENT (ATBD)

ANOMALIES

DATA CITATION GUIDELINES

PRODUCT HISTORY

PUBLICATIONS

GENERAL DOCUMENTATION

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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
lna_temp_nadir_starboard The temperature of the starboard antenna low noise amplifier at ddm_timestamp_utc, in degrees C. degree_Celsius float -9999 N/A 1 N/A
lna_temp_zenith The temperature of the zenith antenna low noise amplifier at ddm_timestamp_utc, in degrees C. degree_Celsius float -9999 N/A 1 N/A
merra2_wind_speed Closest 10 meter referenced MERRA-2 Wind (in lat/lon/time) to L1 sample/ddm. MERRA-2 dataset provides ocean surface vector winds (u,v) on a global 0.5 deg x 0.625 deg, hourly grid. Co-located MERRA-2 winds computed using sqrt(u^2+v^2). See https://disc.gsfc.nasa.gov/datasets/M2I1NXASM_5.12.4/summary?keywords=%22MERRA-2%22 m s-1 float -9999 N/A 1 N/A
nbrcs_mod Derived by passing each MERRA-2 matchup wind speed backwards through the GMF that is consistent with the version of the original observables, accounting for incidence angle of the observation. 1 float -9999 N/A 1 N/A
nbrcs_scatter_area The scattering area of the 3 x 5 region of the ddm used to calculate ddm_nbrcs. meter2 float -9999 N/A 1 N/A
nbrcs_tw_outlier Outliers defined as |Obs_corrected – Mod| > threshold, where threshold = 16 + Mod/2 (nbrcs) or 8 + Mod/2 (les). 0 = False, 1=True, FillValue or NAN = no track-wise correction possible. 1 float -9999 N/A 1 N/A
nbrcs_tw_r2 Fractional variance of the trackwise corrected observable that is explained by the modeled observable. 1 float -9999 N/A 1 N/A
nbrcs_tw_slope The slope of the linear regression between original and modeled observable. 1 float -9999 N/A 1 N/A
nbrcs_tw_yint The y-intercept of the linear regression between original and modeled observable. 1 float -9999 N/A 1 N/A
nst_att_status Nano Star Tracker attitude status as reported by the ADCS subsystem. Enumeration, with 0 indicating OK, and non-zero indicating an erroneous condition. Values: 0 = ok 1 = not_used2 2 = bad 3 = too_few_stars 4 = quest_failed 5 = residuals_too_high 6 = too_close_to_edge 7 = pix_amp_too_low 8 = pix_amp_too_high 9 = backgnd_too_high 10 = track_failure 11 = pix_sum_too_low 12 = unused 13 = too_dim_for_starid 14 = too_many_groups 15 = too_few_groups 16 = channel_disabled 17 = track_blk_overlap 18 = ok_for_starid 19 = too_close_to_other 20 = too_many_pixels 21 = too_many_columns 22 = too_many_rows N/A byte -99 N/A 1 N/A
power_analog 17 x 11 array of DDM bin analog power, Watts. analog_power is the true power that would have been measured by an ideal (analog) power sensor. power_digital is the power measured by the actual 2-bit sensor, which includes quantization effects. power_analog has been corrected for quantization effects. watt float -9999 N/A 1 N/A
power_digital 17 x 11 array of DDM bin digital power, Watts. See power_analog for more information. watt float -9999 N/A 1 N/A
prn_code The PRN code of the GPS signal associated with the DDM. Ranges from 0 to 32. 0 = reflectometry channel idle. 1 through 32 = GPS PRN codes. 1 byte -99 0 to 32 1 N/A
prn_fig_of_merit The RCG Figure of Merit (FOM) for the DDM. Ranges from 0 through 15.The DDMI selects the four strongest specular points (SP) for DDM production. It ranks the strength of SPs using an antenna RCG map. The map converts the position of the SP in antenna azimuth and declination angles to an RCG FOM. 0 represents the least FOM value. 15 represents the greatest FOM value. 1 byte -99 N/A 1 N/A
pvt_timestamp_gps_sec The GPS second of week of pvt_timestamp_utc, with nanosecond resolution. second double N/A N/A 1 N/A
pvt_timestamp_gps_week The GPS week number of pvt_timestamp_utc week int N/A N/A 1 N/A
pvt_timestamp_utc The spacecraft position and velocity epoch. The number of seconds since time_coverage_start with nanosecond resolution. This is the timestamp of the position and velocity reported by the DDMI. This is also the timestamp of the most recent GPS pulse per second. seconds since 2017-03-18 00:00:00.999261282 double N/A N/A 1 N/A
quality_flags Per-DDM quality flags. 1 indicates presence of condition. Flag bit masks: 1/0x00000001 = poor_overall_quality. The logical OR of: tw_corr_outlier large_sc_attitude_err black_body_ddm ddmi_reconfigured spacewire_crc_invalid ddm_is_test_pattern channel_idle low_confidence_ddm_noise_floor sp_over_land sp_very_near_land large_step_noise_floor large_step_lna_temp direct_signal_in_ddm low_confidence_gps_eirp_estimate rfi_detected brcs_ddm_sp_bin_delay_error brcs_ddm_sp_bin_dopp_error gps_pvt_sp3_error sp_non_existent_error brcs_lut_range_error ant_data_lut_range_error bb_framing_error fsw_comp_shift_error sc_altitude_out_of_nominal_range 2/0x00000002 = s_band_powered_up Set if S-band transmitter is powered up. 4/0x00000004 = small_sc_attitude_err Set if the absolute value of the spacecraft roll is between 1 and 30 degrees, the pitch is between 1 and 10 degrees, or the yaw is between 1 and 5 degrees. 8/0x00000008 = large_sc_attitude_err Set if the absolute value of the spacecraft roll is greater than or equal to 30 degrees, the pitch is greater than or equal to 10 degrees, or the yaw is greater than or equal to 5 degrees. 16/0x00000010 = black_body_ddm Set if the black body load was selected during the DDM sampling period. 32/0x00000020 = ddmi_reconfigured Set if the DDMI was reconfigured during the DDM sampling period. 64/0x00000040 = spacewire_crc_invalid Set if the DDM CRC transmitted from the DDMI to the spacecraft computer was not valid. 128/0x00000080 = ddm_is_test_pattern Set if the DDM is a test pattern generated by the DDMI. 256/0x00000100 = channel_idle Set if this reflectometry channel was not tracking a PRN. 512/0x00000200 = low_confidence_ddm_noise_floor Set if the difference between this DDM noise floor and the previous DDM noise floor is greater than 10 percent. 1024/0x00000400 = sp_over_land Set if the specular point is over land. 2048/0x00000800 = sp_very_near_land Set if the specular point is within 25 km of land. 4096/0x00001000 = sp_near_land Set if the specular point is within 50 km of land. 8192/0x00002000 = large_step_noise_floor Set if the difference between this DDM noise floor and the previous DDM noise floor is greater than 0.24 dB. 16384/0x00004000 = large_step_lna_temp Set if the LNA temperature rate of change is greater than 1 degree C per minute. 32768/0x00008000 = direct_signal_in_ddm Set if the absolute value of the difference between direct signal code phase and the DDM signal code phase is less than or equal to four. 65536/0x00010000 = low_confidence_gps_eirp_estimate Set when there is low confidence in the GPS effective isotropic radiated power estimate. 131072/0x00020000 = rfi_detected Set when the kurtosis of the DDM noise floor deviates from pure Gaussian by more than 1.0. 262144/0x00040000 = brcs_ddm_sp_bin_delay_error Set if the calculated specular point bin zero-based delay row is less than 4 or greater than 8. 524288/0x00080000 = brcs_ddm_sp_bin_dopp_error Set if the calculated specular point bin zero-based Doppler column is less than 4 or greater than 6. 1048576/0x00100000 = neg_brcs_value_used_for_nbrcs Set if any bin in the 3 x 5 brcs area used to calculate ddm_nbrcs has a negative value. 2097152/0x00200000 = gps_pvt_sp3_error Cannot calculate GPS SV position/velocity/time from SP3 file. 4194304/0x00400000 = sp_non_existent_error Specular point does not exist. 8388608/0x00800000 = brcs_lut_range_error Unable to index into BRCS uncertainty lookup table. 16777216/0x01000000 = ant_data_lut_range_error Unable to index into antenna data lookup table. 33554432/0x02000000 = bb_framing_error Insufficient black body data for calibration. 67108864/0x04000000 = fsw_comp_shift_error Flight software telemetry encoding error of the fsw_comp_delay_shift and fsw_comp_dopp_shift variables. Corrected in FSW version 4.5. 134217728/0x08000000 = 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 some GPS satellites than others. This flag indicates that Level 1 calibration was based on a GPS antenna gain value with a higher than normal uncertainty. The impact on retrieved wind speed values is typically less than 1 m/s, so this is considered a non-fatal flag. 268435456/0x10000000 = sc_altitude_out_of_nominal_range The spacecraft's altitude is out of nominal altitude range. Nominal altitude is defined as between 490 km to 550 km. 536870912/0x20000000 = tw_corr_outlier Set when track-wise corrected les or nbrcs is flagged as an outlier using this formula: abs(corrected - model) > 8(les) or 16(nbrcs) + 0.5*model. Or if (*_tw_slope < -0.1) or if (*_tw_slope > 5) for both LES and NBRCS. Or if tw_num < 50 * (sampling_rate) where sampling rate is heuristically determined for each track using the formula: round( track_length_samples / track_duration_seconds ). N/A int -9999 N/A 1 N/A
radiometric_antenna_temp The top-of-atmosphere radiometric brightness temperature of the Earth at 1575 MHz and left hand circular polarization, averaged over the nadir antenna pattern in which the specular point lies, in Kelvins. K float -9999 N/A 1 N/A
raw_counts 17 x 11 array of DDM bin raw counts These are the uncalibrated power values produced by the DDMI. 1 int -9999 N/A 1 N/A
rx_clk_bias The receiver clock bias (in seconds) multiplied by the speed of light as reported by the DDMI, interpolated to ddm_timestamp_utc, in meters. meter float -9999 N/A 1 N/A
rx_clk_bias_pvt The receiver clock bias (in seconds) multiplied by the speed of light as reported by the DDMI at pvt_timestamp_utc, in meters. meter float -9999 N/A 1 N/A
rx_clk_bias_rate The receiver clock bias rate (in seconds/second) multiplied by the speed of light as reported by the DDMI, interpolated to ddm_timestamp_utc, in m/s. meter s-1 float -9999 N/A 1 N/A
rx_clk_bias_rate_pvt The receiver clock bias rate (in seconds/second) multiplied by the speed of light as reported by the DDMI, at pvt_timestamp_utc, in m/s. meter s-1 float -9999 N/A 1 N/A
rx_to_sp_range The distance between the CYGNSS spacecraft and the specular point, in meters, at ddm_timestamp_utc. meter int -9999 N/A 1 N/A
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 N/A
sc_alt Spacecraft altitude above WGS-84 ellipsoid, in meters, at ddm_timestamp_utc meter int -9999 N/A 1 N/A
sc_lat Subsatellite point latitude, in degrees North, at ddm_timestamp_utc degrees_north float -9999 N/A 1 N/A
sc_lon Subsatellite point longitude, in degrees East, at ddm_timestamp_utc degrees_east float -9999 N/A 1 N/A
sc_pitch Spacecraft pitch angle relative to the orbit frame, in radians at ddm_timestamp_utc radian float -9999 N/A 1 N/A
sc_pitch_att Spacecraft pitch angle relative to the orbit frame, in radians at att_timestamp_utc radian float -9999 N/A 1 N/A
sc_pos_x The X component of the spacecraft WGS84 reference frame Earth-Centered Earth-Fixed (ECEF) position, in meters, at ddm_timestamp_utc meter int -99999999 N/A 1 N/A
sc_pos_x_pvt The X component of the spacecraft WGS84 reference frame ECEF position, in meters, at pvt_timestamp_utc meter int -99999999 N/A 1 N/A
sc_pos_y The Y component of the spacecraft WGS84 reference frame ECEF position, in meters, at ddm_timestamp_utc meter int -99999999 N/A 1 N/A
sc_pos_y_pvt The Y component of the spacecraft WGS84 reference frame ECEF position, in meters, at pvt_timestamp_utc meter int -99999999 N/A 1 N/A
sc_pos_z The Z component of the spacecraft WGS84 reference frame ECEF position, in meters, at ddm_timestamp_utc meter int -99999999 N/A 1 N/A
sc_pos_z_pvt The Z component of the spacecraft WGS84 reference frame ECEF position, in meters, at pvt_timestamp_utc meter int -99999999 N/A 1 N/A
sc_roll Spacecraft roll angle relative to the orbit frame, in radians at ddm_timestamp_utc radian float -9999 N/A 1 N/A
sc_roll_att Spacecraft roll angle relative to the orbit frame, in radians at att_timestamp_utc radian float -9999 N/A 1 N/A
sc_vel_x The X component of the spacecraft WGS84 reference frame ECEF velocity, in m/s, at ddm_timestamp_utc meter s-1 int -9999 N/A 1 N/A
sc_vel_x_pvt The X component of the spacecraft WGS84 reference frame ECEF velocity, in m/s, at pvt_timestamp_utc meter s-1 int -9999 N/A 1 N/A
sc_vel_y The Y component of the spacecraft WGS84 reference frame ECEF velocity, in m/s, at ddm_timestamp_utc meter s-1 int -9999 N/A 1 N/A
sc_vel_y_pvt The Y component of the spacecraft WGS84 reference frame ECEF velocity, in m/s, at pvt_timestamp_utc meter s-1 int -9999 N/A 1 N/A
sc_vel_z The Z component of the spacecraft WGS84 reference frame ECEF velocity, in m/s, at ddm_timestamp_utc meter s-1 int -9999 N/A 1 N/A
sc_vel_z_pvt The Z component of the spacecraft WGS84 reference frame ECEF velocity, in m/s, at pvt_timestamp_utc meter s-1 int -9999 N/A 1 N/A
sc_yaw Spacecraft yaw angle relative to the orbit frame, in radians at ddm_timestamp_utc radian float -9999 N/A 1 N/A
sc_yaw_att Spacecraft yaw angle relative to the orbit frame, in radians at att_timestamp_utc radian float -9999 N/A 1 N/A
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 N/A N/A 1 N/A
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 N/A 1 to 99 1 N/A
sp_alt Altitude of the specular point relative to the WGS 84 datum in meters, at ddm_timestamp_utc, as calculated on the ground. Note that an approximated DTU10 mean sea surface height model is used to calculate the specular point altitude. meter float -9999 N/A 1 N/A
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