PROCEDURES FOR ESTIMATING RADIO FIELDS PROPAGATED BY MULTIPLE SCATTERING IN THE TROPOSPHERE.
Final rept.(Item 5)
ELECTROMAGNETIC RESEARCH CORP COLLEGE PARK MD
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Tropospheric scatter propagation is considered as a multiple scatter process, the scattering being caused by irregularities of the dielectric structure. For simplicity, the atmospheres statistical properties and its mean refractive index are assumed to depend on altitude only. Radio propagation in such an atmosphere is then considered from the point of view of ray theory. A Monte Carlo calculation, suitable for a fast digital computer, is outlined for computing the multiply scattered fields in a two-dimensional version of the problem. An adaptation is outlined for taking account of diffraction and weak ducting at the earths curved surface. Further adaptations for estimating antenna performance, bandwidth, and azimuthal scattering are proposed. These considerations, and experimental evidence, lead to a statistical normal mode picture of the scatter field at far transhorizon ranges the height-gain function and the statistics of the vertical slope components vary with range only through an exponential rangeattenuation factor. Analytically prescribed atmospheric models, resembling atmospheres encountered in trade-wind inversion areas, are advanced and features of the corresponding statistical normal mode are computed analytically. For practical field computations, mechanization of the Monte Carlo calculation is recommended. Several germane, unsolved problems in the theory are noted. Author