SCATTERING OF VLF RADIO WAVES IN CURVED EARTH-IONOSPHERE WAVEGUIDE

Extensive model studies have been carried out in the past to investigate the effects of ionospheric perturbations on VLF radio propagation in the earth-ionosphere waveguide. In these model studies the surface of the earth is considered flat and the ionosphere is characterized by a finite surface impedance of variable effective height. However, the restrictions for the flat-earth model are not satisfied for modes of near-grazing incidence. As shown before by Wait, a planar structure that supports the desired modes may be constructed simply by modifying the medium of propagation in the straight rectangular dual-model waveguide. As a result of including the earth's curvature in the model, the analysis yields an explanation for the relatively large undulations in the electric field observed at the surface of the earth. The larger undulations in the curved" model are a result of both the modification of the characteristic functions and a larger scattering coefficient. © Copyright 1968 by the American Geophysical Union."