电离层闪烁对星载P波段SAR的影响分析

电离层闪烁会破坏星载合成孔径雷达(SAR)回波信号之间的相关性，使其成像性能下降。已有的工作都是假设已知电离层电子密度的扰动开展的，但是目前的测量手段无法直接获取该参量。该文利用海口观测站超高频(UHF)频段太阳活动高年和中等年份的实测数据，分析电离层闪烁的变化特征，并基于相位屏理论，给出一种利用闪烁指数评估电离层闪烁对星载P波段SAR系统影响效应的方法。结果表明:电离层闪烁在低纬地区主要发生在夜间，且在两分季高发；太阳活动高年，全年约有3.8%的时间会发生电离层闪烁现象；对于P波段SAR系统来说，弱闪烁使得方位向冲激响应函数(IRF)的主瓣宽度和副瓣增益增大，分辨率下降；中等强度闪烁使得方位向冲激响应函数发生严重的扰动，副瓣增益增大到主瓣的水平，主瓣中心也发生平移，可能使得系统无法直接成像。

Effects of Ionospheric Scintillation on P Band Spaceborne SAR

The ionospheric scintillation can destroy the coherence of SAR echos, and correspondingly degrade SAR imaging performance. The previous studies are conducted under the hypothesis of the given ionospheric electron density irregularities, which are unavailable with the current measurement technologies. In this paper, the characteristics of ionospheric scintillations at low latitudes are analysed by using the observational data of Ultra High Frequency　(UHF) band scintillations in the years of high and moderate solar activity at Haikou station. Based on the phase screen theory, a method is proposed to quantify the effects of ionospheric scintillation on P-band spaceborne SAR by using the scintillation index. The results show that the scintillations occur mostly at the night time at low latitudes, especially in equinoxes. The scintillations occur approximately 3.8% during a typical year of high solar activity. For P band SAR, the weak scintillation widens the mainlobe of azimuthal Impulse Response Function (IRF), increases the intensity of sidelobe, and reduces the azimuthal resolution. The moderate scintillation disturbs the IRF seriously, increases the intensity of sidelobe to the degree of mainlobe, and makes the peak of mainlobe shift in azimuthal direction, which can result in the disability of SAR imaging.