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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: 2025-12-14

Documents

USER'S GUIDE

DATA PRODUCT SPECIFICATION

ANOMALIES

DATA CITATION GUIDELINES

PUBLICATIONS

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
add_range_to_sp For diagnostic use only. See UM document 148-0372 CYGNSS L1 netCDF Diagnostic Variables for more information. 1 float -9999 N/A 1
add_range_to_sp_pvt For diagnostic use only. See UM document 148-0372 CYGNSS L1 netCDF Diagnostic Variables for more information. 1 float -9999 N/A 1
att_timestamp_gps_sec The GPS second of week of att_timestamp_utc, with nanosecond resolution second double N/A N/A 1
att_timestamp_gps_week The GPS week number of att_timestamp_utc week int N/A N/A 1
att_timestamp_utc The spacecraft attitude epoch. The number of seconds since time_coverage_start with nanosecond resolution. This is the timestamp of the spacecraft attitude reported by the spacecraft attitude determinination system. seconds since 2021-01-01 00:00:00.499261646 double N/A N/A 1
bb_nearest The time between ddm_timestamp_utc and the ddm_timestamp_utc associated with the closest (in time) black body reading, in signed seconds. A positive value indicates that the black body reading occurred after ddm_timestamp_utc. A negative value indicates that the block body reading occurred before ddm_timestamp_utc. second float -9999 N/A 1
bb_power_temperature_density Raw counts of detected power radiated by the blackbody calibration target, divided by receiver gain and blackbody physical temperature in Kelvins, gives the detected power per unit absolute temperature. Counts/Kelvin float -9999 N/A 1
bit_null_offset_port For diagnostic use only. See UM document 148-0372 CYGNSS L1 netCDF Diagnostic Variables for more information. 1 float -9999 N/A 1
bit_null_offset_starboard For diagnostic use only. See UM document 148-0372 CYGNSS L1 netCDF Diagnostic Variables for more information. 1 float -9999 N/A 1
bit_null_offset_zenith For diagnostic use only. See UM document 148-0372 CYGNSS L1 netCDF Diagnostic Variables for more information. 1 float -9999 N/A 1
bit_ratio_lo_hi_port Bin ratio of the of the port antenna defined as (plus_1_cnts + minus_1_cnts) / (plus_3_cnts + minus_3_cnts). 1 float -9999 N/A 1
bit_ratio_lo_hi_starboard Bin ratio of the of the starboard antenna defined as (plus_1_cnts + minus_1_cnts) / (plus_3_cnts + minus_3_cnts). 1 float -9999 N/A 1
bit_ratio_lo_hi_zenith Bin ratio of the of the zenith antenna defined as (plus_1_cnts + minus_1_cnts) / (plus_3_cnts + minus_3_cnts). 1 float -9999 N/A 1
brcs 17 x 11 array of DDM bin bistatic radar cross section, m^2. The specular point is located in DDM bin round(brcs_ddm_sp_bin_delay_row), round(brcs_ddm_sp_bin_dopp_col). meter2 float -9999 N/A 1
brcs_ddm_peak_bin_delay_row The zero-based delay row of the peak value in the bistatic radar cross section DDM (brcs). Ranges from 0 to 16. 1 byte -99 N/A 1
brcs_ddm_peak_bin_dopp_col The zero-based Doppler column of the peak value in the bistatic radar cross section DDM (brcs). Ranges from 0 to 10. 1 byte -99 N/A 1
brcs_ddm_sp_bin_delay_row The zero-based delay row of the specular point delay in the bistatic radar cross section DDM (brcs). Note that this is a floating point value. 1 float -9999 N/A 1
brcs_ddm_sp_bin_dopp_col The zero-based Doppler column of the specular point Doppler in the bistatic radar cross section DDM (brcs). Note that this is a floating point value. 1 float -9999 N/A 1
commanded_sc_roll Commanded spacecraft attitude roll angle, in radians at ddm_timestamp_utc. This value is updated every 10 seconds from the ENG_HI packet radian 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 byte N/A N/A 1
ddm_ant The antenna that received the reflected GPS signal associated with the DDM. 0 = none 1 = zenith (never used) 2 = nadir_starboard 3 = nadir_port N/A byte -99 N/A 1
ddm_brcs_uncert Uncertainty of the BRCS 1 float -9999 N/A 1
ddm_end_time_offset For diagnostic use only. See UM document 148-0372 CYGNSS L1 netCDF Diagnostic Variables for more information. 1e-9 s int -9999 N/A 1
ddm_kurtosis The kurtosis of the DDM noise floor. For diagnostic use only. See UM document 148-0347 DDM RFI Algorithm for more information. 1 float -9999 N/A 1
ddm_les Leading edge slope of a 3 delay x 5 Doppler bin box that include the specular point bin. The specular point bin is in the top (least delay) row and the center Doppler column of the 3 x 5 box. 1 float -9999 N/A 1
ddm_nbrcs Normalized BRCS of a 3 delay x 5 Doppler bin box that includes the specular point bin. The specular point bin is in the top (least delay) row and the center Doppler column of the 3 x 5 box. 1 float -9999 N/A 1
ddm_noise_floor For non-black-body DDMs: Is equal to the average bin raw counts in the first 45 delay rows of the uncompressed 20 x 128 DDM, in counts, at ddm_timestamp_utc. For black body DDMs: Is equal to the average bin raw counts in all 128 delay rows of the uncompressed 20 x 128 DDM, in counts, at ddm_timestamp_utc. 1 float -9999 N/A 1
ddm_noise_floor_corrected The ddm_noise_floor after a correction factor, based on the nadir antenna bin ratio, has been applied. 1 float -9999 N/A 1
ddm_snr 10log(Smax/Navg), where Smax is the maximum value (in raw counts) in a single DDM bin and Navg is the the average per-bin raw noise counts. ddm_snr is in dB, at ddm_timestamp_utc. dB float -9999 N/A 1
ddm_source The source of the Level 0 DDM raw counts and metadata. 0 = End-End Simulator (E2ES) 1 = GPS signal simulator 2 = CYGNSS spacecraft 3 = Source unknown N/A byte N/A N/A 1
ddm_timestamp_gps_sec The GPS second of week of ddm_timestamp_utc, with nanosecond resolution second double N/A N/A 1
ddm_timestamp_gps_week The GPS week number of ddm_timestamp_utc week int N/A N/A 1
ddm_timestamp_utc DDM sample time. The number of seconds since time_coverage_start with nanosecond resolution. Its position relative to the DDM sampling period is determined by ddm_time_type_selector. Some metadata required for DDM calibration are generated relative to pvt_timestamp_utc or att_timestamp_utc. These metadata are interpolated to ddm_timestamp_utc before being used for DDM calibration. Note that the DDM sampling period is not synchronized with the UTC change of second and can occur at any time relative to the UTC change of second. seconds since 2021-01-01 00:00:00.499261646 double N/A N/A 1
ddm_time_type_selector Determines the position of ddm_timestamp_utc relative to the DDM sampling period. Set to <Middle of DDM sampling period> for nominal science operations. Other settings are used for pre-launch testing only. 0 = Start of DDM sampling period (used for pre-launch testing only) 1 = Middle of DDM sampling period 2 = End of DDM sampling period (used for testing pre-launch only) 3 = pvt_timestamp_utc (used for testing pre-launch only) N/A byte N/A N/A 1
delay_resolution DDM delay bin resolution in chips. One chip is equal to 1/1,023,000 seconds. 1 float N/A N/A 1
dopp_resolution DDM Doppler bin resolution in Hz s-1 float N/A N/A 1
eff_scatter 17 x 11 array of DDM bin effective scattering area, m^2. This is an estimate of the true surface scattering area that contributes power to each DDM bin, after accounting for the GPS signal spreading function. It is calculated by convolving the GPS ambiguity function with the surface area that contributes power to a given DDM bin as determined by its delay and Doppler values and the measurement geometry. The specular point bin location matches the specular point bin location in brcs. meter2 float -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 the specular point location and incidence angle. See UM document 148-0361 Fresnel Coefficient Calculation for more information. 1 float -9999 N/A 1
fsw_comp_delay_shift For diagnostic use only. See UM document 148-0372 CYGNSS L1 netCDF Diagnostic Variables for more information. 1 float -9999 N/A 1
fsw_comp_dopp_shift For diagnostic use only. See UM document 148-0372 CYGNSS L1 netCDF Diagnostic Variables for more information. s-1 float -9999 N/A 1
gps_ant_gain_db_i SV antenna gain in the direction of the specular point. Referenced from the heritage version of gps_eirp (v2.1 and earlier). dBi float -9999 N/A 1
gps_eirp The estimated effective isotropic RF power (EIRP) of the L1 C/A code signal within ± 1 MHz of the L1 carrier radiated by space vehicle, sv_num, in the direction of the specular point, in Watts, at ddm_timestamp_utc. Variations in GPS transmit power are tracked by the direct signal power measured by the navigation receiver. One second samples are smoothed by a ± 10 second running average. watt float -9999 N/A 1
gps_off_boresight_angle_deg SV antenna off boresight angle in the direction of the specular point degree float -9999 N/A 1
gps_tx_power_db_w Power input to SV Tx antenna. Referenced from the heritage version of gps_eirp (v2.1 and earlier). dBW float -9999 N/A 1
inst_gain The black body noise counts divided by the sum of the black body power and the instrument noise power, in count/W, at ddm_timestamp_utc. 1 float -9999 N/A 1
les_scatter_area The scattering area of the 3 x 5 region of the ddm used to calculate ddm_les. meter2 float -9999 N/A 1
lna_noise_figure The low noise amplifier (LNA) noise figure, in dB, at ddm_timestamp_utc. Estimated from pre-launch characterization of LNA performance as a function of LNA temperature. dB float -9999 N/A 1
lna_temp_nadir_port The temperature of the port antenna low noise amplifier at ddm_timestamp_utc, in degrees C. degree_Celsius float -9999 N/A 1
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
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
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