8. N.S. Bellyustin, V. P. Dokuchaev, S, V. Polyakov, et aL, Izv. Vyssh. Uchebn, Zaved., Radtofiz,, 1__.8, No. 9, 1323 (19'/8). 9. S.V. Polyakov, Dissertation, Gor'kii (1982). 10. J. Galejs, Terrestrial Propagation of Long Electromagnetic Waves, Pergamon Press (19'/2). INFLUENCE OF RANDOM STRATIFICATION ON THE INTENSITY OF THE COHERENT COMPONENT OF A UHF SIGNAL BEYOND THE HORIZON A. V. Kukushkin, V. D. Freillkher, and I. M. Fuks UDC 537.876.23:621.371.24 It is shown that in the range of decimeter radio waves the allowance for sufficiently strong anise- tropic inhomogeneities with horizontal scales on the order of hundreds of meters comes down to the solution of the problem of wave propagation in a randomly stratified medium. An estimate of the influence of random stratification on the signal level in the "near" shadow zone, i.e., at distances of 100-200 kin, shows that the signal intensity grows with an increase in the dispersion of large-scale fluctuations of the index of refraction, even if the average gradient of the index of refraction is small and does not result in increased refraction. For systems of radio navigation, radar, and communication lines operating over distances of 100-200 kin, it is interesting to calculate the coherent component of the signal, the level of which can be quite high. According to the data of [1, 2], in about 60% of the cases the amplitude distribution of the signal received in the shadow region differs from a Rayleigh distribution, and this is attributed to the presence of a coherent component. Therefore, one must investigate what factors determine the intensity of the coherent component and its dependence on distance and wavelength. In an experiment one is always dealing with realizations of finite length, and so the concept of coherence must be connected with the averaging time. In the present article we consider the signal component which is coherent over a finite time T and investigate the dependence of its intensity on the statistical characteristics of the random medium and on distance and wavelength. 1. We shall consider the field of a vertical electric dipole, located at the origin of coordinates (r 0 = 0), which can be described by the Debye potential U in the spherical coordinate system r, e, ~o when depolarization effects are neglected. For ka 0 >> 1 (a 0 is the radius of earth, k = 2~/X, and ~. is the wavelength), the radial component of the electric field is connected with the potential U by the simple relation [3] Er = --k2a0U. In accordance with [4], it is convenient to distinguish the attenuation factor W, which varies slowly with the coordinates, in the potential U: U (r) = (e'k~o~ ~) W (r). (1) In the equation for W(r) we change to the coordinate system r = {x, y, zb where x and y are introduced along earth' s surface (the x axis is in the source--receiver direction), while z is normal to it. When the inequalities are satisfied, z/a << l, x>>a/m; oz/ <<H ~' key/ <<~' \ox J one can obtain a parabolic equation for the attenuation factor, 2ik(OW/Ox)+ ~• W + k"(~-z i x, y, z)-- 1)W=O, (2) (3) (4) Institute of Radiophysics and Electronics, Academy of Sciences of the Ukrainian SSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 26, No. 9, pp. 1064-1072, September, 1983. Original article submitted July 26, 1982; revision submitted April 12, 1983. 782 0033-8443/83/2609-0782507.50 O 1984 Plenum Publishing Corporation