利用多頻率距離成像法研究電離層散塊E層場列不規則體之精細結構;A Study on the Structures of Field-Aligned Irregularities in the Sporadic E Layer Using Multiple-Frequency Range Imaging

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题名:	利用多頻率距離成像法研究電離層散塊E層場列不規則體之精細結構;A Study on the Structures of Field-Aligned Irregularities in the Sporadic E Layer Using Multiple-Frequency Range Imaging
作者:	陳帥甫;Chen,Shuai-fu
贡献者:	太空科學研究所
关键词:	距離成像法;電離層;Range Imaging;E
日期:	2016-01-27
上传时间:	2016-03-17 19:14:07 (UTC+8)
出版者:	國立中央大學
摘要:	本篇論文中為使用赤道大氣雷達來觀測電離層散塊E層，為了探討不規則體之精細結構而選用多載頻模式觀測，使用的五組頻率分別為46.5MHz、46.75MHz、47MHz、47.25MHz以及47.5MHz。五組頻率的回波訊號再透過距離成像法來解析徑向距離上的亮度值分布，即回波強度分布，而本篇論文也是首度在電離層使用距離成像法用以分析不規則體。距離成像法的部分則使用傅立葉法以及Capon法來得出亮度值，而亮度圖可能因為雷達訊號在介質中傳遞時產生相位延遲，以及距離權重函數造成的影響，使得亮度圖產生明顯斷層而無法辨識回波訊號。文中說明如何校正才能得出可辨識回波訊號的亮度圖。此次研究之中希望透過距離成像法得到的亮度值，能夠與以往的距離-時間-強度回波圖在解析度上獲得改善。而本次觀測為選用16位元的互補碼加碼觀測，可能由於雷達系統發射互補碼時有些微振幅擾動，或者因為目標物的變動而造成振幅些微改變，導致在解碼過程之中無法將旁波瓣完全消除，造成在亮度圖上還是有少數不連續的部分。為此探討其中的問題而進行互補碼16碼模擬在雷達系統本身或者目標物變動所造成的振幅變動。;In order to investigate the fine structure of irregularities in sporadic E-layer (Es-layer), the Equatorial Atmosphere Radar (EAR) was employed in this study. Five transmitter frequencies were used: 47.0MHz, 47MHz ± 250 kHz and ± 500 kHz. With the data collected from the five frequencies, range imaging was applied to give the brightness distribution (i.e. echo intensity distribution) in the range direction. This thesis is the first study to observe the plasma irregularities in the E-layer by using range imaging. Brightness values can be derived by Fourier method and Capon method. However, the range-time-brightness distribution shows remarkable gaps between range gates, which could be caused by the time delay of the signal in the media and radar system, and range weighting effect. The correction processing to mitigate the gaps of brightness distribution will be carried out in this thesis. The purpose of this research is to improve the range resolution of the radar echo. Moreover, 16 bits complementary codes were used in this observation. And the sidelobes echoes due to the decoding mechanisms appeared occasionally. The sidelobe echoes might be caused by the amplitude perturbations during coding-decoding processing, and/or the fast variations of targets. 16 bits complementary codes were investigated in the simulation to discuss these phenomenon of sidelobe echoes.
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