Wind speed retrieval using GNSS-R technique with geographic partitioning

In this paper,the efect of geographical location on Cyclone Global Navigation Satellite System(CYGNSS)observables is demonstrated for the frst time.It is found that the observables corresponding to the same wind speed vary with geographic location regularly.Although latitude and longitude information is included in the conventional method,it cannot efectively reduce the errors caused by geographic diferences due to the non-monotonic changes of observables with respect to latitude and longitude.Thus,an improved method for Global Navigation Satellite System Refectometry(GNSS-R)wind speed retrieval that takes geographical diferences into account is proposed.The sea surface is divided into diferent areas for independent wind speed retrieval,and the training set is resampled by considering high wind speed.To balance between the retrieval accuracies of high and low wind speeds,the results with the random training samples and the resampling samples are fused.Compared with the conventional method,in the range of 0–20 m/s,the improved method reduces the Root Mean Square Error(RMSE)of retrieved wind speeds from 1.52 to 1.34 m/s,and enhances the correlation coefcient from 0.86 to 0.90;while in the range of 20–30 m/s,the RMSE decreases from 8.07 to 4.06 m/s,and the correlation coefcient increases from 0.04 to 0.45.Interestingly,the SNR observations are moderately correlated with marine gravities,showing correlation coefcients of 0.5–0.6,which may provide a useful reference for marine gravity retrieval using GNSS-R in the future.