The PO.DAAC is pleased to announce the public release of the CYGNSS Science Data Record (SDR) Version 3.0 datasets. The SDR Version 3.0 collection provides a total of 3 unique datasets, each corresponding to processing levels 1 (L1), 2 (L2) and 3 (L3), respectively. While there is quite a large number of variables and measurement parameters in each dataset, the primary measurement in L1 is the Bistatic Radar Cross Section (BRCS) and in both L2 and L3 it is wind speed (meters per second). As a result of the CYGNSS constellation coverage and updates to the SDR version 3.0 processing algorithms, this version of SDR data is made available from 1 August 2018 to present with an approximate forward production latency of 1 to 6 days (nominally under 2 days) in netCDF-4 formatted data files in which data is contained within a 24-hour UTC period. For L1 data, the files are separated according to the specified spacecraft identifier. For L2 and L3 data, the data files represent a daily aggregation from a combination of up to 8 unique CYGNSS spacecraft. More information regarding the CYGNSS mission and instrumentation is available from PO.DAAC’s mission webpage.

SDR version 3.0 represents a substantial improvement over the previous SDR version 2.1. Improvements to the L1 processing, resulting in quality improvements and increased input data availability for L2 and L3 processing, are abbreviated as follows: 1) transmitted GPS signal strength in the direction of the DDM scattering surface is determined in real time from measurements of the direct signal from the GPS satellite to the CYGNSS navigation receiver, allowing for the BRCS calibration to be corrected for variations in GPS transmit power; 2) L1 calibration parameters have been adjusted to produce a best fit to the model population. More details on the processing and algorithm updates can be found within the L1 data landing page.

Improvements to the L2 processing, resulting in direct impacts to the L3 processing, are abbreviated as follows:

1. The Geophysical Model Function (GMF) for fully developed seas (FDS) conditions was generated using matchups between Normalized BRCS measurements and coincident wind speeds produced by NASAs Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) reanalysis model.
2. The GMF for young seas with limited fetch (YSLF) was generated using matchups between Normalized BRCS and coincident wind speeds produced by NOAAs Hurricane Weather Research and Forecast (HWRF) System.
3. Measurements using transmissions from previously discarded GPS satellite block types are reintroduced ; in prior versions, Block II-F was completely discarded due to large variations in GPS transmit power. More details on the processing and algorithm updates can be found within the L2 data landing page. All data updates within the L3 data (available here) are a result of inheritance of changes to the L2 data.

As with all previous versions of the SDR, the L1 and L2 datasets are provided at an approximate binned spatial resolution of 25-km, followed by L3, which is regularly gridded with a binned 0.2° by 0.2° lat/lon spatial resolution. All datasets cover the global tropical oceans within a latitude domain of approximately 40° S to 40° N.

Citations:

1. CYGNSS. 2020. CYGNSS Level 1 Science Data Record Version 3.0. Ver. 3.0. PO.DAAC, CA, USA. Dataset accessed [YYYY-MM-DD] at https://doi.org/10.5067/CYGNS-L1X30
2. CYGNSS. 2020. CYGNSS Level 2 Science Data Record Version 3.0. Ver. 3.0. PO.DAAC, CA, USA. Dataset accessed [YYYY-MM-DD] at https://doi.org/10.5067/CYGNS-L2X30
3. CYGNSS. 2020. CYGNSS Level 3 Science Data Record Version 3.0. Ver. 3.0. PO.DAAC, CA, USA. Dataset accessed [YYYY-MM-DD] at https://doi.org/10.5067/CYGNS-L3X30

Reference: Ruf, C. S., S. Asharaf, R. Balasubramaniam, S. Gleason, T. Lang, D. McKague, D. Twigg, D. Waliser, 2019. In-Orbit Performance of the Constellation of CYGNSS Hurricane Satellites. Bull. Amer. Meteor. Soc., doi: 10.1175/BAMS-D-18-0337.1.

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