The scintillation of extended radio sources when the receiver has a finite bandwidth
The scintillation of extended radio sources when the receiver has a finite bandwidth
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当接收器带宽有限时扩展无线电源的闪烁
DOI：
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发表时间：
1970
期刊：
影响因子：
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通讯作者：
B. Uscinski
中科院分区：
文献类型：
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作者：
K. Budden;B. Uscinski
许多不规则介质的波散射处理都将入射场视为单色平面波。然而，在实践中，特别是在射电天文学中，遇到了一些重要的情况，即入射场不是平面波，而是由有限角大小的源产生的。此外，辐射不是单色的，而是在连续的频带上接收的。本文关注的是当这种场被包含弱随机折射率不规则性的介质散射时产生的波动。这些波动的重要统计特性取决于三个量，这三个量是关于散射场中存在的空间频率的双傅里叶积分。这些函数是散射场分量乘积的集合平均值，是通过研究倾斜入射到弱不规则介质上的波的散射而导出的。物理考虑因素用于显示入射波中的频率扩展和到达角度如何影响介质施加的波动。傅里叶积分的被积函数可以在以后用于解决一般的多重散射问题，但本文的结果仅适用于弱单次散射，当散射体是薄相变屏幕或扩展的不规则介质时。针对光源亮度函数、接收器带通函数和介质不规则性自相关函数的一些特殊情况，给出了闪烁指数、闪烁能见度和接收强度波动的空间自相关函数的公式。对它们进行了简要讨论，以说明当入射场仅部分相干时散射场波动的一些特性。
Many treatments of wave scattering by irregular media take the incident field to be that of a monochromatic plane wave. There are, however, important cases encountered in practice, in particular in Radio Astronomy, when the incident field is not a plane wave, but is produced by a source of a finite angular size. Moreover, the radiation is not monochromatic, but is received over a continuous band of frequencies. The present paper is concerned with fluctuations produced when such a field is scattered by a medium containing weak random irregularities of refractive index. The important statistical properties of these fluctuations are shown to depend on three quantities which are double Fourier integrals with respect to the spatial frequencies present in the scattered field. These functions are assembly averages of products of scattered field components, and are derived by studying the scattering of a wave obliquely incident on a weakly irregular medium. Physical considerations are used to show how a spread of frequencies and angles of arrival, in the incident wave, affect the fluctuations imposed by the medium. The integrands of the Fourier integrals can be used later for the general problem of multiple scatter, but the results in this paper are only for weak single scattering, when the scatterer is either a thin phase changing screen or an extended irregular medium. Formulae are given for the scintillation index, the scintillation visibility, and the spatial autocorrelation function of the fluctuations of received intensity, for some particular cases of source brightness function, receiver bandpass function and autocorrelation function of irregularities in the medium. They are discussed briefly, to illustrate some properties of fluctuations of the scattered field when the incident field is only partially coherent.