星载SAR电离层探测及误差补偿

工作于低频波段的星载合成孔径雷达(SAR)信号会受到电离层的显著影响，因此在系统设计时必须考虑相应的补偿方法。基于此，首先开展了适用于低频大宽带SAR模式的电离层影响评估研究，建立了基于勒让德展开的五阶误差分析模型，可有效解决传统模型各阶次耦合问题。其次，针对背景电离层色散问题，开展了基于双频自聚焦算法的补偿研究，利用ALOS PALSAR数据进行了半物理仿真验证，电离层反演精度优于0.4TECU,可有效提升图像聚焦质量；针对法拉第旋转角误差，利用ALOS PALSAR回波散射矩阵信息开展了补偿研究，结果显示，相比官网提供的补偿参数，误差可进一步降低27%。上述基于回波数据本身的补偿研究，可避免第三方数据精度差、分辨率低、需地面接收机、传播路径不一致等问题，同时降低了载荷成本。最后，结合SAR高分辨率特性，基于回波的电离层反演可有效提高现有电离层探测能力，开展了PALSAR-垂测仪联合反演电子密度研究，其结果比仅垂测仪数据精度普遍提高了30%以上。研究成果可为未来低频星载SAR的系统设计提供技术支撑。

Ionospheric sounding and compensation based on the spaceborne SA

The spaceborne synthetic aperture radar (SAR) at low frequencies can be affected by the ionosphere, the relevant compensation therefore needs to be considered in low-frequency SAR system design. Aiming at this issue, a model of Legendre orthogonal polynomials to evaluate the ionospheric effects was first proposed in this paper, which was suitable for the SAR systems with low frequency and wide band. This new model can avoid coupling of traditional model. Then, based on the signal echo, the compensation techniques for ionospheric dispersion and Faraday rotation were analyzed, which avoided traditional ionosphere data with low accuracy, different paths and ground receiving stations. Based on the autofocus algorithm, the compensation precision of dispersion can reach 04TECU, which can significantly improve the SAR image quality. Compared with the results of official website, a further 27% reduction of Faraday rotation error is achieved according to the information of scattering matrix. At last, the joint observation with PALSAR and ionosonde was applied. The accuracy of the result was improved by 30% compared with the result based on only the ionosonde. This study can provide technical support for the future system design of spaceborne SAR at low frequencies.