Error Analysis in SAR Imaging Due to Fluctuation of Atmospheric Refractive Index
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摘要: 合成孔径雷达(SAR)成像中通常默认大气折射率为1，即电磁(EM)波速率等于自由空间光速且忽略大气吸收特性，但实际存在的吸收会减弱入射功率，电磁波速率的变化会引起相位误差，从而影响图像重建。该文定量分析电磁波速率波动和大气吸收对雷达图像的影响，理论推导得出大气吸收会导致振幅误差，表现为散射点在图像中的重建幅度误差；电磁波速率波动会导致相位误差，表现为散射点在图像中的重建位置误差。仿真实验验证了误差分析的正确性。该分析进一步完备了SAR成像误差分析，有助于SAR图像正确解译。Abstract: Generally, the refractive index of atmosphere is simply 1 by default in Synthetic Aperture Radar (SAR) imaging, that is, the ElectroMagnetic (EM) wave velocity is equal to the speed of light in free-space and the atmospheric absorption is ignored. However, the actual absorption may weaken the incident power and variations in the speed of EM waves may cause phase error, thus affecting image reconstruction. In this paper, the influence of wave velocity fluctuation and atmospheric absorption in SAR imagery is analyzed quantitatively. It is theoretically deduced that the atmospheric absorption will lead to amplitude error, which is shown as strength error of the scatterer in the reconstructed image; EM velocity fluctuation will lead to phase error, which is shown as positioning error of the scatterer in the reconstructed image. The correctness of error analysis is verified by simulation experiments. The work in this paper completes further the SAR imaging error analysis, which is beneficial to SAR image interpretation.
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表 1 电磁波速率误差仿真参数设置
配置 天线到目标距离${R_c}$(km) 大气折射率$n$ 电磁波速率误差$\varDelta {\rm{c}}$(m/s) I 60 $1 + 5 \times 1{0^{ - 4}}$ $1.5 \times 1{0^5}$ II 60 $1 + 8 \times 1{0^{ - 4}}$ $2.4 \times 1{0^5}$ III 30 $1 + 5 \times 1{0^{ - 4}}$ $1.5 \times 1{0^5}$ 
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