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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
sp_fsw_delay 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_inc_angle The specular point incidence angle, in degrees, at ddm_timestamp_utc. This is the angle between the line normal to the Earth's surface at the specular point and the line extending from the specular point to the spacecraft. See UM Doc. 148-0336, CYGNSS Science Data Processing Coordinate Systems Definitions. degree float -9999 N/A 1 N/A
sp_lat Specular point latitude, in degrees North, at ddm_timestamp_utc degrees_north float -9999 N/A 1 N/A
sp_lon Specular point longitude, in degrees East, at ddm_timestamp_utc degrees_east float -9999 N/A 1 N/A
sp_pos_x The X component of the specular point position in the ECEF coordinate system, in meters, at ddm_timestamp_utc, as calculated on the ground. meter int -99999999 N/A 1 N/A
sp_pos_y The Y component of the specular point position in the ECEF coordinate system, in meters, at ddm_timestamp_utc, as calculated on the ground. meter int -99999999 N/A 1 N/A
sp_pos_z The Z component of the specular point position in the ECEF coordinate system, in meters, at ddm_timestamp_utc, as calculated on the ground. meter int -99999999 N/A 1 N/A
sp_rx_gain The receive antenna gain in the direction of the specular point, in dBi, at ddm_timestamp_utc. dBi float -9999 N/A 1 N/A
sp_theta_body The angle between the spacecraft body frame +Z axis and the line extending from the spacecraft to the specular point, 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_theta_orbit The angle between the orbit frame +Z axis and the line extending from the spacecraft to the specular point, 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_vel_x The X component of the specular point velocity in the ECEF coordinate system, in m/s, at ddm_timestamp_utc, as calculated on the ground. meter s-1 int -9999 N/A 1 N/A
sp_vel_y The Y component of the specular point velocity in the ECEF coordinate system, in m/s, at ddm_timestamp_utc, as calculated on the ground. meter s-1 int -9999 N/A 1 N/A
sp_vel_z The Z component of the specular point velocity in the ECEF coordinate system, in m/s, at ddm_timestamp_utc, as calculated on the ground. meter s-1 int -9999 N/A 1 N/A
starboard_gain_setting The Nadir-Starboard Gain Setting (dB, 0=Automatic) dB int -9999 N/A 1 N/A
static_gps_eirp Heritage version of gps_eirp (v2.1 and earlier) that assumed a static value for the power level of the L1 signal transmitted by the GPS satellite, prior to implementation of dynamic gps_eirp monitoring in August 2018. watt float -9999 N/A 1 N/A
status_flags_one_hz One Hz status flags. These flags apply to all four DDMs. 1 indicates presence of condition. Flag masks: 1 = Milky way in zenith antenna field of view 2 = Sun in zenith antenna field of view 4 = Sub-satellite point over open ocean 8 = Sub-satellite point latitude ascending, i.e. sc_lat has increased since the previous DDM sample N/A int -9999 N/A 1 N/A
sv_num The GPS unique space vehicle number that transmitted prn_code. 1 int -9999 N/A 1 N/A
track_id A track is a temporally contiguous series of DDMs that have the same prn_code. Each track in the file is assigned a unique track_id starting with one. track_id ranges from 1 to N, where N is the total number of tracks in the file. 1 int -9999 N/A 1 N/A
tx_clk_bias The GPS spacecraft (sv_num) clock time minus GPS constellation time (in seconds) times the speed of light, in meters. meter float -9999 N/A 1 N/A
tx_pos_x The X component of the GPS spacecraft WGS84 reference frame ECEF position, in meters, at ddm_timestamp_utc meter int -99999999 N/A 1 N/A
tx_pos_y The Y component of the GPS spacecraft WGS84 reference frame ECEF position, in meters, at ddm_timestamp_utc meter int -99999999 N/A 1 N/A
tx_pos_z The Z component of the GPS spacecraft WGS84 reference frame ECEF position, in meters, at ddm_timestamp_utc meter int -99999999 N/A 1 N/A
tx_to_sp_range The distance between the GPS satellite and the specular point, in meters, at ddm_timestamp_utc. meter int -9999 N/A 1 N/A
tx_vel_x The X component of the GPS spacecraft WGS84 reference frame ECEF velocity in meters, at ddm_timestamp_utc meter s-1 int -9999 N/A 1 N/A
tx_vel_y The Y component of the GPS spacecraft WGS84 reference frame ECEF velocity in meters, at ddm_timestamp_utc meter s-1 int -9999 N/A 1 N/A
tx_vel_z The Z component of the GPS spacecraft WGS84 reference frame ECEF velocity in meters, at ddm_timestamp_utc meter s-1 int -9999 N/A 1 N/A
zenith_code_phase The DDMI-measured code phase of the direct GPS signal for prn_code interpolated to ddm_timestamp_utc. 0 <= zenith_code_phase < 1023.0. 1 float -9999 N/A 1 N/A
zenith_sig_i2q2 Raw counts of detected power in direct GPS L1 C/A signal received by zenith navigation antenna and detected by navigation receiver. 1 float -9999 N/A 1 N/A
zenith_sig_i2q2_add_correction The additive correction factor applied with zenith_sig_i2q2_corrected = 10*log10(zenith_sig_i2q2*zenith_sig_i2q2_mult_correction)-zenith_sig_i2q2_add_correction. 1 float -9999 N/A 1 N/A
zenith_sig_i2q2_corrected The zenith_sig_i2q2 after a correction factor, based on the zenith antenna bin ratio, has been applied. 1 float -9999 N/A 1 N/A
zenith_sig_i2q2_mult_correction The multiplicative correction factor applied with zenith_sig_i2q2_corrected = 10*log10(zenith_sig_i2q2*zenith_sig_i2q2_mult_correction)-zenith_sig_i2q2_add_correction. 1 float -9999 N/A 1 N/A
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