Estimation Of High-spatial-resolution VTEC And Three-Dimensional Electron Density With SAR Images

The ionosphere is the ionized part of atmosphere,where there are a large number of free electrons and ions.Research of ionosphere can not only help us better understand the solar-terrestrial space system,but also understand ionospheric impact on telecommunications.Vertical Electron Density Content(VTEC)and three-dimensional electron density are two key ionospheric parameters.Synthetic Aperture Radar(SAR)technology has shown its potential in ionospheric parameters calculation in recent years due to its wide coverage,high spatial resolution,all-weather,all-day.However,current SAR ionospheric research focuses on the two-dimentional VTEC estimation,and the three-dimensional electron density estimation is still limited due to the observation conditions.Based on the above analysis,two new methods are proposed to estimate high-spatial three-dimensional electron density distribution through the integration of full-polarimetric SAR and the international reference ionosphere(IRI)model.Meanwhile,the performance of two methods is evaluated with the incoherent scattering radar(ISR)data.The main contents and results of this paper are as follows:(1).The refined VTEC is estimated through using full-polarimetric SAR images.Based on the relationship between Faraday rotation angle and VTEC,the VTEC distribution with high-spational resolution in low latitude area is constructed and evaluated by the IGS-derived VTEC distribution.The results show that these two VTEC distributions present the similar trend,where the linear coherence between them is 0.99.Additionally,the estimation error is about-0.041?0.177 TECU under ideal conditions,and about-0.692?2.925 TECU under bad conditions.(2).The three-dimensional electron density is estimated by combining of the IRI model electron density profile and SAR VTEC.A new three-dimensional electron density estimation model is proposed based on the fact that VTEC should be equivalent between SAR and IRI.Full-polarimetric ALOS-1/PALSAR-1 images with ascending and descending orbit over Alaska(USA)is processed to obtain the three-dimensional electron density.Comparison of the result between ISR and SAR indicates that proposed method can reduce the electron density error by 17.99% and 36.44%,respectively,demonstrating the rationality of the proposed method.(3).The refined three-dimensional electron density is estimated by combining of the IRI IG value and SAR VTEC.The above method may produce severe estimation error due to the ionospheric height error.In this context,a new three-dimensional electron density estimation model is proposed based on the relationship between IRI IG and VTEC.In order to evaluate the proposed method,the same datasets with last experiment is processed to obtain the three-dimensional electron density.The results show that the proposed method can reduce the electron density errors by 32.10% and37.87% when compared with the IRI model.