Retrieval of Wind Stress at the Ocean Surface From AltiKa Measurements

Wind stress is an important parameter in generating the ocean surface currents. Here, for the first time, we directly estimate this parameter at the ocean surface using all the observations from AltiKa and the accompanying radiometer that affect the wind stress estimates and radar signal propagation through the atmosphere. For this purpose, we used an artificial neural network approach using in situ estimates as the dependent parameter and satellite records as the independent parameters. In the absence of sufficient in situ measurements, wind stress is generally inferred from wind speed at 10-m height obtained from spaceborne scatterometers and altimeters which has been extrapolated to the surface to estimate stress, assuming certain atmospheric conditions that are rarely correct. Hence, we obtained this parameter directly at the ocean surface from satellite records. The estimates for the independent validation data set have a standard deviation of the difference between the in situ and satellite-derived values of 0.032 Nm(-2) with Pearson's correlation coefficient of 0.96 significant at 99% confidence level.