Calibration/validation of ERS-1 scatterometer precision products

As a result of tests performed since ERS-1 launch, the scatterometer archive was reprocessed using improved algorithms at "Centre ERS d'Archivage et de Traitement" located in the "Institut Francais de Recherche pour l'Exploitation de la MER". A model function based upon buoy and model wind data was developed and the Normalized Radar Cross Section (NRCS) observations are shown to fit well with this model function. Scatterometer winds are in good agreement with winds measured on NOAA buoys. Mean standard deviation is of the order of 1.2 m/s for wind speed and 15 degrees for wind direction with no biases. However, some limitations affect the data accuracy: (1) insufficient anisotropy of NRCS's at low incidence angles and low wind speeds results in an increase in the wind direction standard deviations for these conditions, (2) the same underestimation of very high wind speeds (above 20 m/s) as with the Seasat scatterometer is observed and causes are being analysed, (3) effects of the lack of correction for stratification and sea-state on the 10 m neutral wind vector estimate when inversing the scatterometer signals is shown by comparison with NOAA buoy data. Differences with the real-time data provided by the European Space Agency (ESA) are discussed in terms of wind accuracy and in terms of quality control, especially concerning dealiasing skill and sea-ice detection.<
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