Low-frequency reflection in the ionosphere—I

Abstract

A theory of low-frequency reflection in the ionosphere is developed. At wavelengths long compared to the layer thickness, the ionospheric layer is considered as a thin conductive sheet, that leads to a discontinuity of the electromagnetic field. A thicker layer is subdivided into many thin (or differential) sublayers. The field is then thought of as a superposition of many partial waves, each of which is reflected by an individual sublayer. An additional penetrating wave must be assumed. At the lowest frequencies—that is, in the case of thin-sheet reflection—the currents in the layer are horizontal and the reflection is of the metallic type, always showing reversal of the horizontal E-component. Dielectric-type reflection with sign or phase transition at the Brewster angle is obtained at somewhat higher frequencies, if vertical and horizontal current density components are of comparable magnitude. The present first part of the paper deals with the thin-sheet reflection theory and the fundamentals of the general theory. Specialized cases of the general theory and some consequences will be discussed in the second part. The frequencies under consideration are roughly 1–100 kc/s.