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首页> 外文期刊>Journal of Geophysical Research, A. Space Physics: JGR >Doppler Shifted Alpha Transmitter Signals in the Conjugate Hemisphere: DEMETER Spacecraft Observations and Raytracing Modeling
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Doppler Shifted Alpha Transmitter Signals in the Conjugate Hemisphere: DEMETER Spacecraft Observations and Raytracing Modeling

机译：多普勒频移α发射机的信号共轭半球:得墨忒耳的航天器观察和射线追踪建模

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摘要

Alpha navigation transmitters are very low frequency (VLF) transmitters operating at mid-latitudes, which use a specific discrete radiation pattern at three distinct frequencies (11.9, 12.6,and 14.9 kHz). The transmitters are located in the northern hemisphere, but the radiated signals propagate through the magnetosphere to the conjugate hemisphere, where they are detectable by lowaltitude spacecraft. We present an analysis of such signals detected by the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions spacecraft at an altitude of about 660 km. It is found that, due to a Doppler shift, the observed signal frequencies can be at times rather different than the radiated frequencies. This indicates wave propagation at large wave normal angles (close to the resonance cone). Simultaneous observations of the same signal with different Doppler shifts reveal three distinct ways of signal propagation: (i) ducted propagation, (ii) unducted propagation, and (iii) propagation interpreted as only partially ducted. A raytracing analysis is employed to obtain typical wave trajectories corresponding to the individual ways of signal propagation and respective Doppler shifts. A reasonable agreement between the observed and calculated Doppler shifts is obtained. Our results demonstrate the peculiarities of VLF signal propagation throughout the magnetosphere and the possibility of using Doppler shifts to estimate wave normal angles.
机译：α导航发射器非常低频率(甚低频)发射机操作中纬度地区,使用特定的离散辐射模式三种不同的频率(11.9, 12.6,和14.9 kHz)。位于北半球,但通过传播辐射信号磁气圈的共轭半球,他们是被lowaltitude飞船。目前的分析检测到的信号电磁排放的检测传播来自地震地区的航天器约660公里的高度。由于多普勒频移,观察到的信号频率可以有时相当不同辐射的频率。传播波角(接近正常共振锥)。相同与不同的多普勒信号的转变揭示三个不同的信号传播的方法:(我)管道中的传播,(ii) unducted传播和(iii)解释为传播只是部分导管。用来获取典型波轨迹对应于各个信号的方法传播和各自的多普勒频移。合理的观察和之间的协议计算多普勒频移。结果表明甚低频的特点在磁层信号传播并使用多普勒转向的可能性估计波正常角度。

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