Evaluation of wind vectors observed by Oceansat-2 scatterometer using statistical distributions

Statistical distribution of wind speeds and directions observed by the Oceansat-2 scatterometer (OSCAT) over the global oceans are investigated to validate the wind data. Histograms of wind speeds and directions are calculated from the OSCAT wind data and compared with those of wind data from the ECMWF reanalysis to assess systematic errors. The calculated wind speed histograms clearly showed excess concentration at very low wind speed ranges. Dependence on the cross-track wind vector cell location, and differences between the ascending and descending paths, and right and left swaths, found in the previous version, were reduced significantly. Frequency distribution of the wind directions relative to the spacecraft flight direction showed that wind vectors of the OSCAT wind exhibit systematic directional preference relative to the antenna beam directions. The directional modulation relative to the antenna beams significantly varies with wind speed and cross-track cell location. The artificial directivity is considered to be caused by imperfections in the instrument calibration, wind retrieval algorithm, and geophysical model function.