Modeling Of InSAR Ionospheric Delay Correction

Interferometric Synthetic Aperture Radar(InSAR)technology has been widely used in surface deformation monitoring research in recent years due to its unique advantages including wide coverage,high spatial resolution,all-weather,all-day,high precision,and no need for ground control points.However,when the spaceborne SAR signal crosses the ionosphere,it is easily affected by the free electrons in the ionosphere,resulting in the propagation path changes and degradation of the accuracy of deformation observation.It is urgent to carry out the research about the correction of InSAR ionospheric delay errors.A number of scholars have proposed some methods including group delay method,faraday rotation method,azimuth offset method and range split-spectrum method to correct the ionospheric delay phases.Due to the low precision of group delay method,and the limitation for polarization data of faraday rotation method,the range split-spectrum method and the azimuth offset method are the most typical methods to correct the ionospheric delay.However,there still are some problems for both methods in practical applications.The split-spectrum method has a problem of amplified noise effect,and the azimuth offset method has difficulty in determing the optimal parameters of the model.In addition,the correction performance of these two methods is currently less discussed.Based on the above problems,a refined ionospheric delay correction model for split-spectrum method and azimuth offset method is discussed through processing ALOS-1 seismic deformation.Meanwhile,the performance of two methods is compared and evaluated.The main research contents and results of this paper are as follows:Firstly,the effects of microwave SAR signals passing through the ionosphere are analyzed with the aspects of background ionosphere and ionospheric irregularities.Then the faraday rotation,phase advance,group delay and azimuth offset of SAR signals caused by ionospheric effect are derived and discussed,which seriously affects the accuracy of deformation monitoring.Secondly,aiming at the noise suppression for range split-spectrum method and the optimal parameters estimation for azimuth offset method,the refined ionospheric delay correction models are developed.In order to test the performance,the developed models are applied to correct the ionospheric effect on InSAR-derived coseismic deformation on Yushu earthquake and the L'Aquila earthquake.Finally,based on the processing of Yushu earthquake and L'Aquila earthquake,the performance of the range split-spectrum method and azimuth offset method to correct the ionospheric delay correction effects are compared.Meanwhile,the steepest decent method is applied to inverse the sliding distribution of the L'Aquila seismic region.The results show that the range split-spectrum delay can eliminate nearly 70% of the ionospheric phase delay of the interferometric SAR images,and the azimuth offset method can only eliminate about 40% of the ionospheric phase delay.At the same time,the range split-spectrum method can reflect the sliding distribution of seismic faults well.