A THEORY OF INCOHERENT SCATTERING OF RADIO WAVES BY A PLASMA
A THEORY OF INCOHERENT SCATTERING OF RADIO WAVES BY A PLASMA
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DOI：
10.1098/rspa.1960.0212
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发表时间：
1960-01-01
影响因子：
--
通讯作者：
FARLEY, DT
中科院分区：
文献类型：
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作者：
DOUGHERTY, JP;FARLEY, DT
发展了一个描述无碰撞等离子体中电子密度的随机热涨落对无线电波的散射的理论。计算了散射辐射的频谱和幅度。特别注意了频谱中对应于小的多普勒频移的部分，这是与电离层非相干散射现象有关的最重要的区域。这些计算是基于奈奎斯特噪声定理的推广版本，并得出以下结论：(1)电离层的平均散射截面等于每个电子独立散射时的平均散射截面，而每个电子的散射截面是经典汤姆逊截面的一半。(2)散射信号的平均多普勒展宽大致对应于离子的速度，而不是电子的速度。(3)该信号的频谱形状不是高斯的。如图1所示，在远离中心频率的频谱中有一个轻微的最大值。(4)等离子体共振效应对当前感兴趣的频率的散射的贡献可以忽略不计。
A theory is developed which describes the scattering of radio waves by the random thermal fluctuations of electron density in a collision-free plasma. The frequency spectrum, as well as the amplitude, of the scattered radiation is calculated. Particular attention is paid to the part of the spectrum which corresponds to small Doppler shifts, this being the region of greatest significance in connexion with the phenomenon of incoherent scattering from the ionosphere. The calculations are based on a generalized version of Nyquist’s noise theorem, and they lead to the following conclusions: (1) The mean scattering cross-section for the ionosphere is equal to that which would exist if each of the electrons scattered independently with a cross-section of one-half the classical Thomson cross-section. (2) The mean Doppler broadening of the scattered signal corresponds roughly to the speed of the ions rather than to that of the electrons. (3) The spectral shape of this signal is not Gaussian. There is a mild maximum in the spectrum away from the central frequency, as can be seen in figure 1. (4) Plasma resonance effects contribute only negligibly to the scattering for frequencies currently of interest.