An estimate of structural uncertainty in QuikSCAT wind vector retrievals

Fangohr, Susanne and Kent, E.C. (2012) An estimate of structural uncertainty in QuikSCAT wind vector retrievals. Journal of Applied Meteorology and Climatology, 51 (5), 954-961. (doi:10.1175/JAMC-D-11-0183.1).

Abstract

Differences between QuikSCAT level 2b wind vectors from the Jet Propulsion Laboratory (JPL, DIRTH product) and Remote Sensing Systems (RSS, smoothed versions 3.0 and 4.0) for one sample month are presented. Each dataset is derived from the same observations but processing methods result in differences between wind vectors. These differences originate from (1) uncertainty in the geophysical model functions that relate backscatter to wind, (2) noise in the backscatter measurements, and (3) spatial filtering. Statistics of wind vector differences from RSS and JPL are used as an indication of structural uncertainty in QuikSCAT wind retrievals. Grouped 1 m/s bins, systematic differences are largest beyond 20 m/s where RSS version 3.0 (version 4.0) wind speeds can be more than 15 (10) m/s higher (lower) than JPL wind speeds. Below 20 m/s systematic differences on the order of tenths m/s are attributed to differences in the retrieval methods, rain and ice contamination as well as cross-swath position. Even once the recommended data flags are applied, differences in individual wind speed retrievals exceed 10 m/s in a few cases but are much smaller in regions of the swath where the viewing geometry allows more reliable retrievals. In all parts of the swath standard deviation of the differences are smaller than 1.0 m/s. The analyses provide a measure of structural uncertainty in QuikSCAT wind velocity due to the retrieval process, although such comparisons are not able to determine which dataset is closest to the actual wind.

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