联合全极化SAR和IRI估计三维电子密度分布

Estimation of Three-Dimensional Electron Density Distribution Using Polarimetric SAR and IRI Observations

三维电子密度是研究电离层空间结构的关键参数,现有的技术和方法存在空间分辨率不足的缺陷。基于此,提出一种联合全极化合成孔径雷达(synthetic aperture radar,SAR)和国际参考电离层(international reference ionosphere,IRI)模型估计高空间分辨率三维电子密度分布的方法。首先利用全极化SAR计算法拉第旋转(Faraday rotation,FR)角;然后根据FR角结合磁场信息估计垂直总电子含量(vertical total electron content,VTEC);最后联合估计的VTEC和IRI电子密度剖线求解三维空间电子密度分布。为了验证所提方法的可行性,利用覆盖美国阿拉斯加地区的先进陆地观测卫星(advanced land observing satellite,ALOS)-1全极化SAR影像进行了实验,并获取GPS及Poker Flat测站的非相干散射雷达(incoherent scattering radar,ISR)数据对实验结果进行验证。结果发现,相对于IRI三维电子密度,所提方法获取的高空间分辨率三维电子密度整体误差减少了33.57%,其中高于133 km的电子密度误差减少了47.98%。

Objectives:The ionosphere,extending from about 60 km to 1000 km above the earth’s surface,is an important part of the solar-terrestrial space environment.To better understand and characterize the ionosphere,it is necessary to observe the ionospheric parameters such as total electron content(TEC)and three-dimensional(3D)electron density.However,the three-dimensional electron density derived by the current methods is limited due to the low-spatial resolution.A new method combining of full-polarimetric synthetic aperture radar(SAR)and the international reference ionosphere(IRI)model is proposed to estimate highspatial 3D electron density distribution.Methods:Firstly,we calculate Faraday rotation(FR)angles from full polarimetric SAR data.Then,we estimate vertical total electron content(VTEC)using FR angles and geomagnetic field information,and reconstruct 3D electron density distribution by combining IRI electron density profile with SAR-derived VTEC.Results:Application of the proposed method to ALOS-1 full-polarization SAR images with descending and ascending orbits over the region of Alaska shows that,for Experiment 1 with ascending orbit,SAR-derived VTEC is consistent with GPS-derived VTEC and the difference between them is about 3.1 TECU(total electron content unit).For Experiment 2 with descending orbit,the difference between SAR-derived VTEC and incoherent scattering radar(ISR)VTEC is only 0.2 TECU.When comparing with the electron density derived from ISR,the standard deviations has decreased by 33.57%for the proposed method,and the standard deviations has decreased by 47.98%at the attitude over 133 km.Conclusions:It can be concluded that it is capable to estimate high-spatial-resolution VTEC and 3D electron density from full-polarization SAR images.These products can help us better understand the characteristics of ionospheric variation in space.