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Description

This Level 1 (L1) dataset contains the Version 3.1 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. This version supersedes Version 3.0; https://doi.org/10.5067/CYGNS-L1X30. 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 6 days (or better) from the last recorded measurement time. Here is a summary of improvements the calibration and processing changes to the Version 3.1 data: The CYGNSS science antenna gain patterns have been adjusted to improve the accuracy of the ocean surface scattering cross section (a.k.a. the NBRCS) calibration. They are adjusted so that the annual average observed NBRCS matches the model-predicted average as derived from Wavewatch-3 estimates of the surface roughness with the appropriate spectral tail extension added to the roughness spectrum. The adjustment is made independently at each position in the science antenna pattern. A correction for coarse quantization effects by the on-board digital processor has also been added. This reduces the effects of radio frequency interference, which appeared as calibration biases in the v3.0 L1 NBRCS and retrieval biases in the v3.0 L2 wind speed that were persistent at certain locations.

Product Summary

Platforms
CYGNSS
Instruments
DDMI
Spatial Extent

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

Spatial Resolution
25000 Meters x 25000 Meters
Coordinate System
CARTESIAN
Granule Spatial Representation
CARTESIAN
Temporal Extent
2018-08-01
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
C2146321631-POCLOUD
Data State
ACTIVE
Number of Files/Granules
15964
Processing Level
1
Published
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. (2021). CYGNSS Level 1 Science Data Record Version 3.1 [Data set]. NASA Physical Oceanography Distributed Active Archive Center. https://doi.org/10.5067/CYGNS-L1X31 Date Accessed: 2026-05-30

Documents

USER'S GUIDE

DATA PRODUCT SPECIFICATION

ANOMALIES

DATA CITATION GUIDELINES

PUBLICATIONS

GENERAL DOCUMENTATION

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
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
noise_correction The correction factor applied with ddm_noise_floor = (ddm_noise_floor_uncorrected*noise_correction). 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
port_gain_setting The Nadir-Port Gain Setting (dB, 0=Automatic) dB int -9999 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
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 2021-01-01 00:00:00.499261646 double N/A N/A 1 N/A
quality_flags First group of the Per-DDM quality flags. 1 indicates presence of condition. More quality flags can be found in quality_flags_2. Flag bit masks: 1/0x00000001 = poor_overall_quality. The logical OR of the following flags. If any one of the following flags are set then poor_overall_quality will be set: 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 low_quality_gps_ant_knowledge sc_altitude_out_of_nominal_range anomalous_sampling_period invalid_roll_state incorrect_ddmi_antenna_selection(quality_flags_2) sp_in_sidelobe(quality_flags_2) fatal_nst_outage(quality_flags_2) low_zenith_ant_gain(quality_flags_2) poor_bb_quality(quality_flags_2) poor_quality_bin_ratio(quality_flags_2) 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. Referenced using a map with 0.1 degree lat/lon bins. Coastline features or islands smaller than bin size may not be properly captured. 2048/0x00000800 = sp_very_near_land Set if the specular point is within 25 km of land. Referenced using a map with 0.1 degree lat/lon bins. 4096/0x00001000 = sp_near_land Set if the specular point is within 50 km of land. Referenced using a map with 0.1 degree lat/lon bins. 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 Not enough data is available to properly calibrate the NBRCS for this sample's GPS satellite. 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 = anomalous_sampling_period Set when an anomaly was observed on the CYGNSS or GPS satellite while this sample was taken. These samples have produced data that do not align with typical CYGNSS results. See up to date list at: https://docs.google.com/spreadsheets/d/1AFAZanVGDApLSnJQAAdPfOKoJQs0jnB8ZvIuD1Z5mAc/edit?usp=sharing 1073741824/0x40000000 = invalid_roll_state The spacecraft’s reported roll angle is more than 1 degree from the commanded roll. N/A int -9999 N/A 1 N/A
quality_flags_2 Second group of the Per-DDM quality flags. 1 indicates presence of condition. The first group of quality flags can be found in quality_flags. Flag bit masks: 1/0x00000001 = incorrect_ddmi_antenna_selection The wrong (port or starboard) antenna was selected. 2/0x00000002 = high_signal_noise The signal is in the highest noise group, but there are still some OK noise rows. Samples are suspect, but may contain quality data. Flag only used for land applications. 4/0x00000004 = noise_floor_cal_error The signal is off or is very near the top rows of the full DDM. A proper noise floor cannot be computed. Flag only used for land applications. 8/0x00000008 = sp_in_sidelobe The specular point is in the sidelobe causing low confidence in the antenna gain. 16/0x00000010 = negligible_nst_outage Minor star track outage with negligible impact on attitude knowledge 32/0x00000020 = minor_nst_outage Minor star track outage with small but acceptable impact on attitude knowledge 64/0x00000040 = fatal_nst_outage Star track outage with unacceptable impact on attitude knowledge 128/0x00000080 = low_zenith_ant_gain Zenith antenna gain is less than -6 dB 256/0x00000100 = poor_bb_quality The distance between the surrounding BB samples > 1350 seconds OR the absolute value of the time to the nearest BB > 350 seconds. 512/0x00000200 = poor_quality_bin_ratio Bin ratio on the nadir or zenith antenna is associated with degraded performance. N/A int -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
sp_az_body Let line A be the line that extends from the spacecraft to the specular point, at ddm_timestamp_utc. Let line B be the projection of line A onto the spacecraft body frame XY plane. sp_az_body is the angle between the spacecraft body frame +X axis and line B, in degrees, at ddm_timestamp_utc. See UM Doc. 148-0336, CYGNSS Science Data Processing Coordinate Systems Definitions. degree float -9999 N/A 1 N/A
sp_az_orbit Let line A be the line that extends from the spacecraft to the specular point at ddm_timestamp_utc. Let line B be the projection of line A onto the orbit frame XY plane. sp_az_orbit is the angle between the orbit frame +X axis (the velocity vector) and line B, in degrees, at ddm_timestamp_utc. See UM Doc. 148-0336, CYGNSS Science Data Processing Coordinate Systems Definitions. degree float -9999 N/A 1 N/A
sp_ddmi_delay_correction For diagnostic use only. See UM document 148-0372 CYGNSS L1 netCDF Diagnostic Variables for more information. 1 float -9999 N/A 1 N/A
sp_ddmi_dopp For diagnostic use only. See UM document 148-0372 CYGNSS L1 netCDF Diagnostic Variables for more information. s-1 float -9999 N/A 1 N/A
sp_ddmi_dopp_correction For diagnostic use only. See UM document 148-0372 CYGNSS L1 netCDF Diagnostic Variables for more information. s-1 float -9999 N/A 1 N/A
sp_delay_error For diagnostic use only. See UM document 148-0372 CYGNSS L1 netCDF Diagnostic Variables for more information. 1 float -9999 N/A 1 N/A
sp_dopp_error For diagnostic use only. See UM document 148-0372 CYGNSS L1 netCDF Diagnostic Variables for more information. s-1 float -9999 N/A 1 N/A
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