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Description
This Level 1 (L1) dataset contains the Version 2.1 geo-located Delay Doppler Maps (DDMs) calibrated into Power Received (Watts) and Bistatic Radar Cross Section (BRCS) expressed in units of meters squared from the Delay Doppler Mapping Instrument aboard the CYGNSS satellite constellation. This version supersedes Version 2.0. 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. The Version 2.1 release represents the second science-quality release. Here is a summary of improvements that reflect the quality of the Version 2.1 data release: 1) data is now available when the CYGNSS satellites are rolled away from nadir during orbital high beta-angle periods, resulting in a significant amount of additional data; 2) correction to coordinate frames result in more accurate estimates of receiver antenna gain at the specular point; 3) improved calibration for analog-to-digital conversion results in better consistency between CYGNSS satellites measurements at nearly the same location and time; 4) improved GPS EIRP and transmit antenna pattern calibration results in significantly reduced PRN-dependence in the observables; 5) improved estimation of the location of the specular point within the DDM; 6) an altitude-dependent scattering area is used to normalize the scattering cross section (v2.0 used a simpler scattering area model that varied with incidence and azimuth angles but not altitude); 7) corrections added for noise floor-dependent biases in scattering cross section and leading edge slope of delay waveform observed in the v2.0 data. Users should also note that the receiver antenna pattern calibration is not applied per-DDM-bin in this v2.1 release.
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
C2251464384-POCLOUD
Data State
ACTIVE
Number of Files/Granules
24647
Processing Level
1
Published
Updated
Science Keywords
Radar Cross-Section
,
Radar Reflectivity
,
SIGMA NAUGHT
,
Flight Data Logs
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
Citation Copied
CYGNSS. (2017). CYGNSS Level 1 Science Data Record Version 2.1 [Data set]. NASA Physical Oceanography Distributed Active Archive Center. https://doi.org/10.5067/CYGNS-L1X21 Date Accessed: 2026-05-01
CYGNSS. “CYGNSS Level 1 Science Data Record Version 2.1.” NASA Physical Oceanography Distributed Active Archive Center, 2017. doi:10.5067/CYGNS-L1X21. Date Accessed: 2026-05-01
CYGNSS. CYGNSS Level 1 Science Data Record Version 2.1. NASA Physical Oceanography Distributed Active Archive Center, 2017, doi:10.5067/CYGNS-L1X21. Date Accessed: 2026-05-01
Radar Cross-Section, Radar Reflectivity, SIGMA NAUGHT, Flight Data Logs
Soil Moisture retrieval in Southeast China from spaceborne GNSS-R measurements
Dong, Zhounan, Jin, Shuanggen
Radar Cross-Section, Radar Reflectivity, SIGMA NAUGHT, Flight Data Logs
Lake level and surface topography measured with spaceborne GNSSreflectometry from CYGNSS mission: Example for the lake Qinghai
Li, Weiqiang, Cardellach, Estel, Fabra, Fran, Ribo, Serni, Rius, Antonio
Radar Cross-Section, Radar Reflectivity, SIGMA NAUGHT, Flight Data Logs
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.
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
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
N/A
att_timestamp_gps_sec
The GPS second of week of att_timestamp_utc, with nanosecond resolution
second
double
N/A
N/A
1
N/A
att_timestamp_gps_week
The GPS week number of att_timestamp_utc
week
int
N/A
N/A
1
N/A
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 2020-01-02 00:00:00.499261690
double
N/A
N/A
1
N/A
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
int
-9999
N/A
1
N/A
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
N/A
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
N/A
bit_ratio_hi_lo_port
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
bit_ratio_hi_lo_starboard
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
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
N/A
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
N/A
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
N/A
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
N/A
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
N/A
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
N/A
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
N/A
ddm_brcs_uncert
Uncertainty of the BRCS
1
float
-9999
N/A
1
N/A
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
N/A
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
N/A
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
N/A
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
N/A
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
N/A
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
N/A
ddm_timestamp_gps_sec
The GPS second of week of ddm_timestamp_utc, with nanosecond resolution
second
double
N/A
N/A
1
N/A
ddm_timestamp_gps_week
The GPS week number of ddm_timestamp_utc
week
int
N/A
N/A
1
N/A
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 2020-01-02 00:00:00.499261690
double
N/A
N/A
1
N/A
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
N/A
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
N/A
direct_signal_snr
10log(zenith signal power/zenith signal noise) in dB, at ddm_timestamp_utc.
dB
float
-9999
N/A
1
N/A
dopp_resolution
DDM Doppler bin resolution in Hz
s-1
float
N/A
N/A
1
N/A
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
N/A
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
N/A
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
N/A
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
N/A
gps_ant_gain_db_i
SV antenna gain in the direction of the specular point
dBi
float
-9999
N/A
1
N/A
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 CYGNSS spacecraft, in Watts, at ddm_timestamp_utc.
watt
float
-9999
N/A
1
N/A
gps_off_boresight_angle_deg
SV antenna off boresight angle in the direction of the specular point
degree
float
-9999
N/A
1
N/A
gps_tx_power_db_w
GPS Tx power in dBW
dBW
float
-9999
N/A
1
N/A
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
N/A
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
N/A
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
N/A
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
N/A
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
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
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.