電離層閃爍對星載P波段SAR的影響分析
doi: 10.11999/JEIT140948
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2.
(中國電波傳播研究所 青島 266107)
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3.
(西安電子科技大學物理與光電工程學院 西安 710071)
基金項目:
國家國際科技合作專項(2011DFA22270)資助課題
Effects of Ionospheric Scintillation on P Band Spaceborne SAR
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1.
(School of Physics and Optoel Ectronic Engineering, Xidian University, Xi&rsquo
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2.
(China Research Institute of Radiowave Propagation, Qingdao 266107, China)
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3.
(School of Physics and Optoel Ectronic Engineering, Xidian University, Xi&rsquo
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摘要: 電離層閃爍會破壞星載合成孔徑雷達(SAR)回波信號之間的相關性，使其成像性能下降。已有的工作都是假設已知電離層電子密度的擾動開展的，但是目前的測量手段無法直接獲取該參量。該文利用?？谟^測站超高頻(UHF)頻段太陽活動高年和中等年份的實測數據，分析電離層閃爍的變化特征，并基于相位屏理論，給出一種利用閃爍指數評估電離層閃爍對星載P波段SAR系統(tǒng)影響效應的方法。結果表明：電離層閃爍在低緯地區(qū)主要發(fā)生在夜間，且在兩分季高發(fā)；太陽活動高年，全年約有3.8%的時間會發(fā)生電離層閃爍現(xiàn)象；對于P波段SAR系統(tǒng)來說，弱閃爍使得方位向沖激響應函數(IRF)的主瓣寬度和副瓣增益增大，分辨率下降；中等強度閃爍使得方位向沖激響應函數發(fā)生嚴重的擾動，副瓣增益增大到主瓣的水平，主瓣中心也發(fā)生平移，可能使得系統(tǒng)無法直接成像。Abstract: 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.
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Key words:
- SAR /
- Ionospheric scintillation /
- P band /
- Phase screen /
- Resolution
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