电离层闪烁对星载P波段SAR的影响分析
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摘要
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。
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.
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.
引文
[1]邓云凯,赵凤军,王宇.星载SAR技术的发展趋势及应用浅析[J].雷达学报,2012,1(1):1-10.Deng Yun-kai,Zhao Feng-jun,and Wang Yu.Brief analysis on the development and application of spaceborne SAR[J].Journal of Radars,2012,1(1):1-10.
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[6]Mc Namara L F,Caton R G,Parris R T,et al..Sinnatures of equatorial plasma bubbles in VHF satellite scitillations and equatorial ionograms[J].Radio Science,2013,48(2):89-101.
[7]Franke S J,Liu C H,and Fang D J.Mulrifrequency study of ionospheric scintillation at Ascension island[J].Radio Science,1984,19(3):695-706.
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[12]Xu Z W,Wu J,and Wu Z S.Potential effects of the ionosphere on space-based SAR imaging[J].IEEE Transactions on Antennas and Propagation,2008,56(7):1968-1975.
[13]郑虎,李廉林,李芳.电离层对星载合成孔径雷达方位向分辨率影响的分析[J].电子与信息学报,2008,30(9):2085-2088.Zheng Hu,Li Lian-lin,and Li Fang.Study about ionospheric effects on spaceborne SAR azimuth imaging[J].Journal of Electronics&Information Technology,2008,30(9):2085-2088.
[14]李力,杨淋,张永胜,等.电离层不规则体对P波段星载SAR成像的影响[J].国防科技大学学报,2013,35(5):158-162.Li Li,Yang Lin,Zhang Yong-sheng,et al..Effects of ionospheric irregularities on spaceborne P band SAR imaging[J].Journal of National University of Defense Technology,2013,35(5):158-162.
[15]李亮,洪峻,明峰,等.电离层时空变化对中高轨SAR成像质量的影响分析[J].电子与信息学报,2014,36(4):915-922.Li Liang,Hong Jun,Ming Feng,et al..Study of ionospheric effects induced by spatio-temporal variability on medium-earth-orbit SAR imaging quality[J].Journal of Electronics&Information Technology,2014,36(4):915-922.
[16]Ngwira C M,Klenzing J,Olwendo J,et al..A study of intense ionospheric scintillation observed during a quiet day in the East African low-latitude region[J].Radio Science,2013,48(4):396-405.
[17]Rino C L.A power law phase screen model for ionospheric scintillation:1.Weak scatter[J].Radio Science,1979,14(6):1135-1145.
[18]Aarons J.Global morphology of ionospheric scintillations[J].Proceedings of the IEEE,1982,70(4):360-378.
[19]甄卫民,冯健,陈丽,等.多站多路径GPS信号研究低纬电离层不均匀体[J].电波科学学报,2007,22(1):138-142.Zhen Wei-min,Feng Jian,Chen Li,et al..Investigation of low-latitude ionospheric irregularities by using multi-station GPS multi-link signals[J].Chinese Journal of Radio Science,2007,22(1):138-142.
[2]Rignot E,Zimmermann J R,and Vanzyl J J.Spaceborne applications of P-band imaging radars for measuring forest biomass[J].IEEE Transactions on Geoscience and Remote Sensing,1995,33(5):1162-1169.
[3]Ishimaru A,Kuga,Y,Liu J,et al..Ionospheric effects on synthetic aperture radar at 100 MHz to 2 GHz[J].Radio Science,1999,34(1):257-268.
[4]刘传保.电离层对雷达测量精度的影响及校正方法研究[J].航天电子对抗,2013,29(2):47-53.Liu Chuan-bao.The effects of ionosphere to radar measurement precision and the correction methods[J].Aerospace Electronic Warfare,2013,29(2):47-53.
[5]Emardson R,Jarlemark P,Johansson J,et al..Spatial variability in the ionosphere measured with GNSS networks[J].Radio Science,2013,48(5):646-652.
[6]Mc Namara L F,Caton R G,Parris R T,et al..Sinnatures of equatorial plasma bubbles in VHF satellite scitillations and equatorial ionograms[J].Radio Science,2013,48(2):89-101.
[7]Franke S J,Liu C H,and Fang D J.Mulrifrequency study of ionospheric scintillation at Ascension island[J].Radio Science,1984,19(3):695-706.
[8]Quegan S and Lamont J.Ionospheric and tropospheric effects on synthetic aperture radar performance[J].International Journal of Remote Sensing,1986,7(4):525-539.
[9]Rogers N C and Quegan S.Simulation of ionospheric effects and their mitigation for the ESA BIOMASS P-band space-based radar[C].Proceedings of the Ionospheric Effects Symposium,Alexandria,VA,USA,2011:13A3-1-13A3-8.
[10]Tsynkov S V.On SAR imaging through the earth’s ionosphere[J].SIAM Journal on Imaging Sciences,2009,2(1):140-182.
[11]Gilman M,Smith E,and Tsynkov S V.Reduction of ionospheric distortions for spaceborne synthetic aperture radar with the help of image registration[J].Inverse Problems,2013,29(5):054005(1-35).
[12]Xu Z W,Wu J,and Wu Z S.Potential effects of the ionosphere on space-based SAR imaging[J].IEEE Transactions on Antennas and Propagation,2008,56(7):1968-1975.
[13]郑虎,李廉林,李芳.电离层对星载合成孔径雷达方位向分辨率影响的分析[J].电子与信息学报,2008,30(9):2085-2088.Zheng Hu,Li Lian-lin,and Li Fang.Study about ionospheric effects on spaceborne SAR azimuth imaging[J].Journal of Electronics&Information Technology,2008,30(9):2085-2088.
[14]李力,杨淋,张永胜,等.电离层不规则体对P波段星载SAR成像的影响[J].国防科技大学学报,2013,35(5):158-162.Li Li,Yang Lin,Zhang Yong-sheng,et al..Effects of ionospheric irregularities on spaceborne P band SAR imaging[J].Journal of National University of Defense Technology,2013,35(5):158-162.
[15]李亮,洪峻,明峰,等.电离层时空变化对中高轨SAR成像质量的影响分析[J].电子与信息学报,2014,36(4):915-922.Li Liang,Hong Jun,Ming Feng,et al..Study of ionospheric effects induced by spatio-temporal variability on medium-earth-orbit SAR imaging quality[J].Journal of Electronics&Information Technology,2014,36(4):915-922.
[16]Ngwira C M,Klenzing J,Olwendo J,et al..A study of intense ionospheric scintillation observed during a quiet day in the East African low-latitude region[J].Radio Science,2013,48(4):396-405.
[17]Rino C L.A power law phase screen model for ionospheric scintillation:1.Weak scatter[J].Radio Science,1979,14(6):1135-1145.
[18]Aarons J.Global morphology of ionospheric scintillations[J].Proceedings of the IEEE,1982,70(4):360-378.
[19]甄卫民,冯健,陈丽,等.多站多路径GPS信号研究低纬电离层不均匀体[J].电波科学学报,2007,22(1):138-142.Zhen Wei-min,Feng Jian,Chen Li,et al..Investigation of low-latitude ionospheric irregularities by using multi-station GPS multi-link signals[J].Chinese Journal of Radio Science,2007,22(1):138-142.
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