Wind Fields Retrieved From Dual-Polarization SAR Under Typhoon Sea States And Numerical Simulation Of Wind-Rain Coupled Microwave Scattering

Accurate access to the wind field information of typhoons is a hotspot in marine and atmospheric sciences and a key to accurately predicting the intensity and path of typhoons.In this thesis,the wind field information of typhoon is obtained by C-band dual-polarized synthetic aperture radar(SAR)image,and the scattering mechanism of precipitation on radar signal is studied.Under extreme meteorological conditions,the wind streaks produced by the vortex of the atmospheric boundary layer on the sea surface are obvious on the SAR image.Therefore,the wind direction of the storm can be obtained by analyzing the wind streaks in the SAR image.In the low wind speed region,the signal-to-noise ratio of VH polarization is small,but VV polarization is large;in the high wind speed region,the VH polarization signal is not saturated,but for VV,the signal is saturated.Therefore,it is possible to simultaneously retrieve the wind direction using VV and VH polarized SAR images.Finally,a typhoon wind direction product with a spatial resolution of 25 km was obtained by using the local gradient method(LG).Statistical verifications with buoys,GPS-dropsondes,scatterometers,microwave radiometers,and H*Wind show that the wind direction bias and root mean square error(RMSE)are 17.14°and-4.20°,respectively.In the retrieval of the dual-polarized SAR typhoon wind speed,the cost function is constructed by using the low wind speed and high wind speed GMF.The wind direction obtained by the local gradient method is input into the cost function,and the wind speed is obtained when the minimum value of the cost function is shown.Comparing with the wind speed obtained by SFMR observation,it is found that the wind speed obtained from the GMF is not high in the low wind speed region,the high wind speed region is not low,the RMSE is 4.1 m/s,and the bias is 0.9 m/s.Therefore,this thesis retrieves the wind field of sea surface directly from SAR image,without the input of external information,which reduces the error and improves the accuracy of wind speed retrieval.When retrieving the sea surface wind field,we found that the impact of precipitation on the radar signal is significant.In this paper,a wind-rain coupled microwave scattering model is proposed.Under high wind speed conditions,wind,turbulence,wave breaking and atmospheric effects on radar signals are considered.Using the data matched by SFMR and Hurricane Irma SAR image,we verified the wind-rain coupling model in the high wind speed region.The simulation results are in good agreement with the observed results.The RMSE is 0.94 dB and the bias is 0.01 dB.