3D Modelling Method of VLF Subionospheric Radio Wave Propagation Allowing for a Localized Ionospheric Perturbation

Abstract

The problem of radio wave propagation allowing for a 3D localized lower ionospheric irregularity appears in accordance with the necessity of the theoretical interpretation of VLF remote sensing data. The various processes in the Earth's crust and in the terrestial environment (earthquakes, magnetic storms, sporadic E-layers, lightning-induced electron precipitations, rocket launches, artificial ionosphere heating, nuclear explosions, etc.) may cause ionospheric perturbations with different intensity and size. This paper presents a full-wave numerical-analytical method for the 3D radio wave propagation problem. We consider the VLF field by a vertical electric dipole in the Earth-ionosphere waveguide with an irregularity in the lower ionosphere as an example. The impedance non-uniform waveguide model is constructed. In the scalar approximation, the problem is reduced to the surface integral equation for Hertz's vector component. Using an asymptotic (kr ≫ 1) integration along the transverse direction to the propagation path, we transform this equation to the one-dimensional integral equation taking into account the field scattered by the irregularity. This last one is solved by combining the semi-inversion method and the subsequent iterations. The proposed technique is useful for the study of both small- and large-scale irregularities. Numerical results of VLF point source field diffraction from a truncated highly conducting cylinder are presented. © 2004, The Institute of Electrical Engineers of Japan. All rights reserved.