Scattering of radio waves by electrons above the ionosphere
Scattering of radio waves by electrons above the ionosphere
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电离层上方电子对无线电波的散射
DOI：
10.1029/jz065i006p01851
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发表时间：
1960
期刊：
影响因子：
--
通讯作者：
E. Salpeter
中科院分区：
文献类型：
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作者：
E. Salpeter
Gordon[1958]建议使用电离层和更高海拔电子的雷达散射作为测量温度和电子密度随海拔变化的一种工具。沿着这些线已经进行了一些观测[Bowles，1959，Pineo，Kraft，and Briscoe，1960]，未来还会有更详细的观测，包括测量散射信号频谱的详细形状。
设D=(KT/4πNe~2)1/2是电子的德拜长度，其中T是温度，n是电子的粒子密度；λ是无线电波的波长，θ是散射角。无量纲参数α=λ/4πD SiN 12θ是确定散射辐射频谱的重要参数。如果是α≪1，我们有来自单个电子的纯非相干散射[戈登，1958年]，频谱具有由电子热速度产生的多普勒展宽的高斯型特征。费耶[1960]最近详细分析了α≫-1的情况，无论是当碰撞平均自由程较长时，还是当它与无线电波的波长相比较短时。本说明的目的是指出，与单位相当的α的中间情况的频谱显示出一些有趣的特征。在500Mc/S或更低的雷达频率下，过渡区α∼-1出现在1000公里或更高的高度，电子的碰撞可以忽略不计。也忽略了地球磁场的影响，并假定雷达频率与电子气的等离子体频率相比很大。在这些假设和忽略电子碰撞的情况下，结果如下：
Gordon [1958] has suggested the use of radar scattering from the electrons in the ionosphere and at greater altitude as a tool for measuring temperature and electron density as a function of altitude. Some observations along these lines have already been made [Bowles, 1959, Pineo, Kraft, and Briscoe, 1960], and more detailed observations are to be expected in the future, including measurements of the detailed shape of the frequency spectrum of the scattered signal.
Let D = (kT/4πne2)1/2 be the electron Debye length, where T is the temperature and n is the particle density of the electrons; and let λ be the wavelength of the radio wave and θ the scattering angle. The dimensionless parameter α = λ/4πD sin 12θis of importance in determining the frequency spectrum of the scattered radiation. If a α≪1, we have purely incoherent scattering from individual electrons [Gordon, 1958] and the frequency spectrum has a Gaussian shape characteristic of the Doppler broadening produced by the electron thermal velocity. The case of a α≫1 has been analyzed in detail recently by Fejer [1960], both when the collision mean free path is long and when it is short compared with the wavelength of the radio wave. The purpose of the present note is to point out that the frequency spectrum for the intermediate cases, of α comparable with unity, shows some interesting features. At radar frequencies of 500 Mc/s or less, the transition region α∼1 occurs at heights of the order of 1000 km or more, where collisions of the electrons can be neglected. The effect of the earth's magnetic field is also omitted and the radar frequency is assumed to be very large compared with the plasma frequency of the electron gas. With these assumptions and the neglect of electron collision, the results are as follows: