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Description

This CYGNSS Level 1 (L1) science data record dataset contains the version 3.2 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 3.1: https://doi.org/10.5067/CYGNS-L1X31. 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. <br><br>
The correction for coarse quantization effects that was implemented in v3.1 for the signal portion of the DDM has been updated to include a correction to the noise floor portion of the DDM. This update is found to improve the sensitivity to soil moisture over land and to have a minimal effect on the sensitivity to wind speed over ocean. An update is made to the correction for the temperature dependence of the receiver electronics. This update reduces slow variations in calibration bias associated with a ~60 day oscillation in the mean temperature of the satellites. L1 variables over land and ocean are now combined in common netcdf data files, with additional details added regarding the specular point calculation over land. Nadir (science) antenna pattern and NBRCS rescaling has been updated to improve the inter-satellite consistency of the L1 calibration.<br><br>
The CYGNSS is a NASA Earth System Science Pathfinder Mission that is intended to collect the first frequent space‐based measurements of surface wind speeds in the inner core of tropical cyclones. Made up of a constellation of eight micro-satellites, the observatories provide nearly gap-free Earth coverage using an orbital inclination of approximately 35° from the equator, with a mean (i.e., average) revisit time of seven hours and a median revisit time of three hours. This inclination allows CYGNSS to measure ocean surface winds between approximately 38° N and 38° S latitude. This range includes the critical latitude band for tropical cyclone formation and movement.

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
C2832195379-POCLOUD
Data State
ACTIVE
Number of Files/Granules
20245
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. (2024). CYGNSS Level 1 Science Data Record Version 3.2 [Data set]. NASA Physical Oceanography Distributed Active Archive Center. https://doi.org/10.5067/CYGNS-L1X32 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 2018-08-15 00:00:00.999261540 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
coherency_ratio Estimation of the ratio of received power between the central bins and periphery bins of the raw_counts DDM after the elimination of noise bins [4]. A higher ratio is more indicative of signal coherence. 1 float -9999 N/A 1
coherency_state Meaning of each confidence state value: 0 = Not coherent 1 = Coherent 2 = Mixed Coherence 3 = Indeterminate Coherence 1 byte -99 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
comp_ddm_sp_delay_row TBD 1 float -9999 N/A 1
comp_ddm_sp_doppler_col TBD 1 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
ddmi_tracker_delay_center The navigation receiver clock drift contribution to the received signal Doppler frequency. Estimated during the 1Hz DMR navigation velocity solution as receiver clock bias rate, converted to frequency (Hz). N/A float -9999 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_nadir_bb_correction_next The correction factor applied to the next blackbody value based on the nadir bin ratio. 1 float -9999 N/A 1
ddm_nadir_bb_correction_prev The correction factor applied to the previous blackbody value based on the nadir bin ratio. 1 float -9999 N/A 1
ddm_nadir_signal_correction The correction factor applied to signal value based on the nadir bin ratio. 1 float -9999 N/A 1
ddm_nbrcs Normalized BRCS over an interpolated 3 delay x 5 Doppler region around the precise inter-bin specular point location [2]. The specular point bin is in the top (least delay) row and the center Doppler column of the 3 x 5 box. This value is computed only over the ocean due to the high confidence in the ocean specular point location. For land NBRCS values use ddm_nbrcs_center and ddm_nbrcs_peak. 1 float -9999 N/A 1
ddm_nbrcs_center Approximation of the DDM NBRCS using a fixed and centered delay/Doppler grid in the BRCS DDM. Calculated by dividing the sum of a 3x5 grid of the BRCS DDM (brcs) by the sum of the equivalent grid from the effective scattering area DDM (eff_scatter). The grid region consists of 3 delay bins and 5 Doppler bins centered at delay bin 9 and Doppler bin 5 (using zero based indexing) of the BRCS and effective area DDMs. Computed only over land. 1 float -9999 N/A 1
ddm_nbrcs_peak Approximation of the DDM NBRCS using the peak DDM only. Calculated by dividing the BRCS DDM peak bin (brcs) by the single central effective scatter area bin (eff_scatter). Computed only over land. 1 float -9999 N/A 1
ddm_nbrcs_scale_factor Scale factor applied to the ddm_nbrcs during the statistical de-biasing process. 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_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 2018-08-15 00:00:00.999261540 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 &lt;Middle of DDM sampling period&gt; 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
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