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Public Release of RapidScat Level 2B Climate Ocean Wind Vectors in 12.5km Footprints Version 2.0

Wednesday, April 11, 2018

The PO.DAAC is pleased to announce the public release of the “RapidScat Level 2B Climate Ocean Wind Vectors in 12.5km Footprints Version 2.0” (hereafter L2B Version 2.0) dataset. This dataset consists of Version 2.0 L2B science-quality ocean surface wind vector retrievals from the RapidScat Ku-band scatterometer aboard the International Space Station (ISS). Unlike QuikSCAT, ISS-RapidScat is not in sun-synchronous orbit, and flies at roughly half the altitude with a low inclination angle that restricts data coverage to the tropics and mid-latitude regions; the extent of latitudinal coverage stretches from approximately 61 degrees North to 61 degrees South. This dataset release represents a complete historical reprocessing of the RapidScat L2B climate-quality data record starting from the beginning of the mission on 8 October 2014 and ending on 19 August 2016. L2B data are in an along-track/cross-track swath grid with a pixel (wind vector cell) resolution of 12.5 km. This resolution is achieved through a slice composite technique in which high-resolution slice measurements from L1B data are composited into a 12.5 km wind vector cell.

Version 2.0 processing begins with the same L1B (time-ordered backscatter) data as used in the previous Version 1.0 processing. Version 2.0 improves upon the previous Version 1.0 processing by fundamentally adjusting the baseline geophysical model function (GMF) using a sea-surface temperature (SST) dependent GMF developed by Lucrezia Ricciardulli (Remote Sensing Systems) which fixes persistent wind speed retrieval biases over colder ocean surface conditions. The next improvement is with regard to quality flagging, in which the entire flagging schema is simplified, and additional quality flags are provided in both the “flags” and “eflags” variables to enable users with even more quality filtering capability. One final change to the Version 2.0 dataset is the inclusion of a new global attribute called “rev_status”, which specifies whether RapidScat was measuring in either the original (highest data quality) high SNR mode or one of the four low SNR time periods, the latter of which indicates the accuracy of winds below 5 m/s is degraded. This new global attribute also serves to identify what are referred to as “marginal” orbits in which there are large gaps in the data record due to suboptimal spacecraft attitude. Other than gaps in the data, the accuracy of the winds in the “marginal” orbits are similar to other orbits.

Each L2B file is provided in netCDF-4 format and corresponds to a specific orbital revolution (rev) number, which begins at the southernmost point of the ascending orbit. This is the official dataset produced by the ISS-RapidScat Project’s Science Data Systems (SDS) Team at the Jet Propulsion Laboratory (JPL). An updated Level 2B user guide has been drafted and will be published in the near future pending an internal review process.

More information, documentation, read software and access to the dataset may be gained through the PO.DAAC Web Portal by visiting this URL:

https://podaac.jpl.nasa.gov/dataset/RSCAT_LEVEL_2B_OWV_CLIM_12_V2

Users who have any further questions or concerns are encouraged to visit our Forum site: https://podaac.jpl.nasa.gov/forum/.