Tuesday, March 5, 2024

The PO.DAAC is pleased to announce the public release of the (Cyclone Global Navigation Satellite System) CYGNSS Science Data Record (SDR) Version 3.2 (V3.2) Level 1 (L1) DDM calibration, Level 2 (L2) wind speed retrieval, Level 3 fully developed seas (L3 FDS) gridded wind speed, and Level 3 merged (L3 MRG) wind speed data products. L3 MRG is a new product which combines the L2 FDS and Young Seas Limited Fetch (YSLF) winds and eliminates the need to choose between them depending on sea state development and the proximity to storms. The data are provided in netCDF-4 format and extend from 1 August 2018 to the present with an approximate 6 day latency. Improvements to the v3.1 L1 and L2 algorithms, and additional descriptions of the L3 products are documented below:

L1 – 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.

L2 – The L2 Geophysical Model Function (GMF) that maps L1 observables to ocean surface wind speed and the Significant Wave Height (SWH) second order correction to the wind speed retrievals were rederived to be consistent with the v3.2 L1 calibration. The method used for deriving the GMF and SWH correction is the same as for v3.1. An additional swell wave correction has been added to better account for the long wave dependence at low wind speeds. The FDS and YSLF retrieval algorithms are otherwise the same as v3.1. The v3.2 L2 YSLF wind speed is now designated as an intermediate product and should not be used ‘as is’. Additional quality control filters have been added to the Level 3 gridded product derived from the L2 YSLF wind speed to detect and remove outlier L2 samples, and use of the L3 product is recommended.

L3 FDS – The v3.2 L3 gridded wind speed product inherits the v3.2 L2 FDS data as input at the same temporal and spatial resolution as the Level 2 data, sampled on consistent 0.2 by 0.2 degree latitude by longitude grid cells. The L3 gridding algorithm is unchanged. Range Corrected Gain (RCG) has been added to the L3 netcdf files as a new data field.

L3 MRG – The L3 Merged Storm (MRG) wind speed product combines CYGNSS Storm-Centric Gridded (SCG) wind speeds, which are derived from the L2 YSLF winds for a region surrounding a given tropical cyclone (TC), with L3 FDS winds away from the TC center. A tapered weighted averaging scheme is used centered on the 34-knot wind radius (R34) of the storm. The R34 value in each storm quadrant is also reported. The algorithm produces global (+/- 40 deg latitude) wind speeds reported on a 0.1x0.1 deg grid every 6 hours for each tropical cyclone, although some 6-hourly increments may be missing if there are an insufficient number of satellite overpasses of the storm during that time interval. The netCDF files are output on a storm-by-storm basis.

The CYGNSS datasets and documents are accessible via the dataset landing page on PO.DAAC web portal. Users are recommended to download the data using the podaac-data-subscriber. We also encourage users to visit PO.DAAC Cloud Data Page for detailed information about how to access the data from NASA Earthdata Cloud. General information regarding the CYGNSS mission is available from the mission website.

Please note that the production of the v3.1 will end after 30 days from the release of the v3.2 data.



Ruf, C., D. McKague, D. Posselt, S. Gleason, M.P. Clarizia, V. Zavorotny, T. Butler, J. Redfern, W. Wells, M. Morris, J. Crespo, C. Chew, E. Small, D. Pasqual, T. Wang, A. Warnock, D. Mayers, M. Al-Khaldi, A. O’Brien. CYGNSS Handbook (2nd ed.), Michigan Publishing Services, Ann Arbor, MI, ISBN 978-1-60785-549-1, https://doi.org/10.3998/mpub.12741920, 227 pp, 2022.

Mayers, D. R., C. S. Ruf, A. M. Warnock, “CYGNSS Storm-Centric Tropical Cyclone Gridded Wind Speed Product,” J. Appl. Meteor. Climatol., doi: 10.1175/JAMC-D-22-0054.1, 2023. 

Comments/Questions? Please contact podaac@podaac.jpl.nasa.gov or visit the PO.DAAC on Earthdata Forum.