On the interaction of radio waves with meteoric plasma
On the interaction of radio waves with meteoric plasma
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无线电波与流星等离子体的相互作用
DOI：
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发表时间：
1998
期刊：
影响因子：
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通讯作者：
L. Foschini
中科院分区：
文献类型：
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作者：
L. Foschini
本文从物理的角度分析了流星等离子体，着重讨论了它与无线电波的相互作用。讨论了流星等离子体的一些宏观特征，指出电子-离子碰撞频率并不是人们通常认为的可以忽略的。关于后向散射和前向散射的区别，值得注意的是，这两个系统使用的无线电波类型不同。前向散射雷达使用连续正弦波，而后向散射雷达使用脉冲波。这不仅影响了解决这个问题的数学方法，也影响了物理理论。后向散射雷达的脉冲波形可以用几个不同频率的分量之和来表示。由此得出的结论是，在传播期间，各种分量倾向于相对于彼此改变相位，这导致脉冲形状的改变。因此，色散关系取决于频率，并且可以用泰勒级数来表示。脉冲在介质中传播的详细处理不是本文的主题：感兴趣的读者可以在例如Oughstun&Sherman(1997)中找到有用的数学工具。这里我们只想强调，我们不能简单地将后向散射雷达发射的信号视为正弦信号：因此，将后向散射回波理论推广到前向散射是不正确的。这篇文章的目的是解决流星物理中的一些基本概念，我们给其他文章留下了一个“烹饪书”的方法。为了简单起见，研究了射频范围内的正弦波与流星等离子体的相互作用。我们将看到，关于流星是一种无碰撞的电离气体的常见假设没有任何物理依据。
In this paper, a meteoric plasma is analyzed from a physical viewpoint, with particular emphasis on its interaction with radio waves. The attention is drawn to some macroscopic characteristics of a meteoric plasma and it is shown that the electron-ion collision frequency is not negligible, as commonly thought. Concerning the difference between back-scattering and forward-scattering, it is worth noting that the two systems use different types of radio waves. A forward-scattering radar uses a continuous sine wave, while a back-scattering one uses a pulsed wave. This influences the mathematical approach to the prob- lem, but also physical theories. The pulse shape of the back- scattering radar can be represented by a sum of several com- ponents with different frequencies. It follows that, during the propagation, the various components tend to change phase with respect to one another, which leads to a change in shape of the pulse. The dispersion relation thus depends on the frequency and can be expressed in a Taylor series. A detailed treatment of the pulse propagation in dielectrics is not the subject of this pa- per: the interested reader can find useful mathematical tools in, for example, Oughstun & Sherman (1997). Here we want only to underline that we cannot simply consider the signal emit- ted by a back-scattering radar as sinusoidal: thus, the extension of the back-scattering echo theory to forward-scattering is not correct. The purpose of this paper is to settle some basic concepts in meteor physics and we leave a "cook-book" approach to other articles. The interaction of sine waves (for the sake of simplicity) in the radio frequency range with meteoric plasma is investigated. We will see that the common assumption about meteors as a collisionless ionized gas does not have any physical ground.