从电离层垂直反射的二次回波的統計特性

在地面上用无线电方法研究电离层时,通常只利用电离层反射的一次回波,但是利用二次回波来研究电离层也是可能的。利用二次回波提供的补充知识,特別是利用一次和二次回波的同时观测结果的相互对比,在某些情况下,对电离层物理和电波传播的研究,具有特别的意义。在这篇文章中,将对垂直採测时从电离层反射的二次回波波場和振幅的统计特性,以及一次和二次回波之间的统计联系,进行一些理论上的计算;并根据这些计算结果,讨论一下利用二次回波研究电离层和电波传播吋的若干问題。

STATISTICAL CHARACTERISTICS OF SECOND-ORDER ECHOES OF RADIOWAVE REFLECTED VERTICALLY FROM THE IONOSPHERE

In the study of ionospheric drift, the first-order echoes of radiowave reflected vertically from the ionosphere are usually employed. In this paper, attention is drawn to the possibility to deduce the parameters of ionospheric irregularities and drift from the fading records of second-order echoes observed by three close-spaced receivers. The author considered the reflection of radiowave from the ionosphere as diffraction by an equivalent screen on which the wave field is distributed at random. It is shown that the spatial and temporal correlation functions of second-order echoes field ρ_E2（ξ,η,τ） may be expressed in terms of field correlation functions of first-order echoes ρ_E1（1/2ξ,1/2η,τ） and ρ_E1（3/2ξ,3/2η,τ）. Therefore, the amplitude correlation function ρ_A1 of first-order echoes may be predicted from the observed amplitude correlation function ρ_A2 of second-order echoes, and vice versa. In other words, parameters of ionospheric irregularities and drift may be deduced from either the first or the second order echoes, and the applicability of the equivalent screen theory, the physical basis of the correlation analysis methods in the study of ionospheric drift, may be tested experimentally by comparing the results obtained simultaneously from first and second echoes. The influence of the small-scale irregularities on the measurement of radiowave absorption in the ionosphere is also discussed. It is shown that when the fluctuation of amplitude is caused merely by the small-scale irregularities, the ionospheric absorption L is given by the equation L=-10log（4 ₂²/₁²）. This is contrary to Ataev's results.