短基线三角形多频台阵的行进式电离层扰动传播特性观测研究

TID (Travelling Ionospherci Disturbances) is a frequent phenomenon in the ionosphere. The observation and the research of temporal and spatial variations of TID are very important for people to understand energy propagation and dissipation in the middle and upper atmosphere.Nowadays this has become one of the research focuses of space weather. However, there exist presently such some problems in current sounding methods of TID as the number of sounding frequencies in high frequency Doppler array is few, there is no horizontal propagation component in ionosonde, distribution density is larger and there is no height information of ionospheric disturbances in satellite beaconing for TEC, and the time of observation is limited and detecting is only performed at fixed heights in airglow observation et al. In order to solve the above prolems, this project presents a short baseline multi-frequency observation array, which is comprised of one transmitting spot, three receiving spots, and synchronization systems controlled by Global Position System (GPS), to obsrve and study the characteristic of propagation and variation of TID. The horizontal variation of TID is measeured by using spatial measurement in multi-point with the short baseline observation system. The vertival variation of TID is measured by using the multi-frequency observation system. Thus the Doppler frequency shifts of different reflection points and different heights are obtained. Then the Doppler frequency shifts are analyzed by adopting time-frequency analysis method of non-single disturbance field to extract some disturbance parameters of TID like the period, the magnitude, and the propagation velocity et al. In the end, the profile of ionospheric movements is inversed by Dopplionograms. After long-term continual observations are carried out, the statistical characteristic of ionospheric disturbances during quiet period and the evolution characteristic of ionospheric disturbances during magnetic storm in the center of China are presented. This offers a continual and effective way to observe and study the characteristic of propagation and variation of TID by experimental methods.

行进式电离层扰动(TID)是电离层中经常发生的现象,观测研究这些扰动的时空变化特性对于理解高层大气中能量传播与耗散过程具有十分重要作用,是当前空间天气研究的热点之一。针对目前TID探测方法中高频多普勒阵探测频点少、测高仪无水平传播参量、卫星信标TEC布站密度大且无高度信息以及气辉观测时间受限且在固定高度等现状，本项目探索一种短基线三角形多频台阵(由1点发射和3点接收,并用GPS收发同步探测的多频系统构成),对TID传播变化特性进行观测研究。利用短基线多点空间探测实现TID水平空间变化测量，利用多频探测实现TID高度变化测量，通过获得不同反射点、不同高度回波信号的多普勒频移，采用非单一场时频分析方法提取TID扰动周期、幅度和传播速度等参量，并反演电离层运动剖面。通过连续观测，给出中国中部地区电离层扰动的统计变化特性以及磁暴期间的演变特性，为实验观测研究TID传播变化特性提供一种连续有效手段。

本项目自主设计了用于电离层扰动传播特性探测的软硬件试验平台，研制出一套高速度、超敏捷、小型化、可移动、高性能的电离层数字测高仪PDI（Portable Digital Ionosonde）/电离层多频多普勒数据发射接收机。由于PDI体积重量轻，天线尺寸小，易于安装，建站容易，便于流动观测等特点，非常适合于在中低纬地区临时建站、一发多收，并与其它同站观测设备如GNSS，VHF雷达等开展联合观测，是中低纬电离层中经常出现的小尺度/短周期的电离层扰动特性观测的极佳手段。开展了中低纬电离层扰动结构的统计分析,中低纬电离层不规则结构和闪烁形态特征以及触发机制；赤道电离异常的变化特征与低纬电离层不规则结构和闪烁出现率之间物理机制等，丰富了中低纬电离层扰动探测的理论基础和实验支撑。利用PDI的多频多普勒探测功能开展了中低纬电离层扰动结构及运动特性的实地观测研究，取得了有新意的观测研究结果。首先，利用基于单频信号相位变化率测量的实时探测方法，在PDI上快速获取了连续高精度多频多普勒频高图，多普勒频移分辨率高达0.039Hz，多普勒频高图探测周期小于1 分钟，通过反演得到了电离层电子浓度等值面法向运动速度和垂直扰动速度等信息，进而推演出电离层扰动随时间和空间的实时变化特征，通过对这些时域信号的频谱分析，发现这些扰动主要是由极区活动激发的我国中部地区常在冬季出现的中尺度TID。其次，将PDI部署在三亚低纬站进行连续观测，结果表明：周期在几分钟到数十分钟的短周期电离层扰动在F层的不同高度上被同时观测到，通过与同站布置的TEC接收机的测量结果进行比较，发现二者具有良好的一致性，都观测到这种短周期的电离层扰动从F层较低高度一直传播到F2层临界频率附近的较高高度上。但对于F层最底端的一种短周期扰动，后来被证实为Brunt-Väisälä周期的扰动波，仅仅被PDI观测到，而TEC接收机并未明显观测到它,这些结果充分显示PDI用于观测研究周期小到几分钟的电离层扰动现象的强大性能，为下一步有效推广应用这种经济有效的扰动传播探测打下良好基础。