Abstract
Spaceborne altimeters are an important data source for obtaining global sea surface wind speeds (U10). Although many altimeter U10 algorithms have been proposed and they perform well, there is still room for improvement. In this study, the data from ten altimeters were collocated with buoys to investigate the error of the altimeter U10 retrievals. The U10 residuals were found to be significantly dependent on many oceanic and atmospheric parameters. Because these oceanic and atmospheric parameters are intercorrelated, an asymptotic strategy was used to isolate the impact of different parameters and establish a neural-network-based correction model of altimeter U10. The results indicated that significant wave heights and mean wave periods are effective in correcting U10 retrievals, probably due to the tilting modulation of long-waves on the sea surface. After the wave correction, the root-mean-square error between the U10 from altimeters and buoys was reduced from 1.45 to 1.24 m/s and the impacts of thermodynamic parameters, such as sea surface (air) temperate, became negligible. The U10 residuals after correction showed that the atmospheric instability can lead to errors on extrapolated buoy U10. The buoy measurements with large air-sea temperature differences need to be excluded in the Cal/Val of remotely sensed U10.
Highlights
S EA surface wind speed is one of the key environmental parameters in marine and atmospheric sciences
The U10 is the most important impact factor of the Radar Cross-Sections (RCSs), the RCS can have some secondary response to other oceanic and atmospheric parameters, such as the significant wave height (SWH), Mean Wave Period (MWP), Sea Surface Temperature (SST), and Sea Surface Air Temperature (SSAT), which has been confirmed by previous studies using scatterometer and Synthetic Aperture Radar (SAR) data (e.g., [10]–[12])
The impact of these secondary responses on altimeter U10 retrievals was analyzed using the colocations between ten satellite altimeters and 52 National Data Buoy Center (NDBC) buoys
Summary
S EA surface wind speed is one of the key environmental parameters in marine and atmospheric sciences. Among these remote sensors, scatterometers have the widest swath and the best overall accuracy (with a typical error of ∼1 m/s) [2], making them an irreplaceable data source of U10. Wave crests are usually rougher than wave troughs, which is a very important effect for retrieving sea surface height termed electromagnetic bias (e.g., [16]) It may impact U10 retrievals because the RCS is a “linear average” over the ∼7 km footprint for the 1-Hz data.
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