The ionospheric propagation of low- and very-low-frequency radio waves over distances less than 1000 km
The ionospheric propagation of low- and very-low-frequency radio waves over distances less than 1000 km
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DOI：
10.1049/pi-3.1951.0043
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发表时间：
1951-05
期刊：
影响因子：
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通讯作者：
R. Bracewell;K. G. Budden;J. Ratcliffe;T. Straker;K. Weekes
中科院分区：
文献类型：
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作者：
R. Bracewell;K. G. Budden;J. Ratcliffe;T. Straker;K. Weekes
在过去的几年里，卡文迪什实验室的大部分无线电研究都与低频和极低频波的传播有关。该文件构成了一个总结的结果，各种实验，这是在单独的文件中详细描述，其中一些尚未公开。10各种独立的方法测量波的反射的视高度的结果表明，波的16？30 kc/s的反射，就像是从一个位于（72 ± 3）km高度的有明显边界的水平面反射一样。反射的视高度随太阳的角度有规律地变化，其变化可用一个方程来概括。频率30的波？150 kc/s似乎是从大约75公里的高度斜入射反射的，但有一些证据表明，它们可能是从高达10公里的高度垂直入射反射的。发现在所有频率下的波的偏振在陡入射时近似为圆形，但在斜入射时（65），频率为16 kc/s的波是线性偏振的。在较高的频率上，没有测量斜入射时的偏振。波的吸收随频率的变化非常迅速？在夏季，转换系数从16 kc/s时的约0.15变化到70 kc/s时的0.002。在所有频率上，在陡入射角和斜入射角下，观察到日出附近行为的重要差异。突然的电离层扰动对反射波的影响进行了讨论，并解释为意味着反射的表观高度的减少;反射波的振幅几乎没有改变16 kc/s，但在较高的频率大大减少。最后，非常简要地讨论了超长无线电波反射理论的现状。
In the last few years a large part of the radio research at the Cavendish Laboratory has been concerned with the propagation of waves of low and very low frequency. The paper constitutes a summary of the results of the various experiments, which are described in detail in separate papers, some of which are as yet unpublished.3?10 The results of various independent methods of measuring the apparent height of reflection of the waves show that waves of 16?30 kc/s are reflected as if from a sharply bounded horizontal surface situated at a height of (72 ± 3) km when the sun is overhead. The apparent height of reflection varies regularly with the angle of the sun and its variation may be summarized by an equation. The waves of frequency 30?150 kc/s appear to be reflected from a height of about 75 km at oblique incidence, but there is some evidence that they may be reflected from as much as 10 km higher at vertical incidence. The polarization of the waves at all frequencies is found to be approximately circular at steep incidence, but at oblique incidence (65 ) waves of a frequency of 16 kc/s are linearly polarized. No measurements of polarization at oblique incidence have been made on the higher frequencies. The absorption of the waves changes very rapidly with frequency?on a summer day the conversion coefficient varies from about 0.15 at 16 kc/s to 0.002 at 70 kc/s. Important differences in behaviour near sunrise are observed on all frequencies at steep incidence and oblique incidence. The effects of a sudden ionospheric disturbance on the reflected waves are discussed and interpreted as implying a decrease in the apparent height of reflection; the amplitude of the reflected wave is scarcely altered on 16 kc/s, but is much decreased on higher frequencies. Finally, the present state of the theory of reflection of very long radio waves is discussed very briefly.