Influence of the Earth’s Ionosphere on the Polarization Characteristics of Radio Waves in the Megahertz Range

Abstract

This work is devoted to the study of the influence of the Earth’s ionosphere on the polarization characteristics of radio waves in the megahertz range. The relevance of the work is determined by the need to improve methods for calculating radiation passing through ionospheric plasma layers and reflected from them, in order to solve modern problems of radio communication, radar and radio navigation, as well as problems of remote sensing of the Earth from space. The megahertz range is interesting in that it allows subsurface sounding of the earth’s covers. In this paper, we consider the frequency range that is borderline for the applicability of the concept of “Faraday rotation”, that is, we consider the frequencies for which the idea of the propagation of radio waves with ordinary and extraordinary polarization along the same trajectory is very conditional. The analysis of the influence of the Earth’s ionosphere on the parameters of high-frequency radio signals is carried out depending on the spatial model of the ionospheric plasma, geographical coordinates, orientation of the magnetic field, and ionospheric irregularities. These characteristics include rotation of the polarization vector (angle of Faraday rotation), phase shift (phase deviation), deviation of the aiming angle, deviation of the radio signal trajectory from a straight line, and others. To calculate the above characteristics, a bicharacteristic system of equations was used in the work. In the process of numerical simulation, it was assumed that the radiation source is located on a moving spacecraft at a distance of several hundred kilometers from the Earth’s surface, the angle of inclination of the rays varies relative to the positive direction of the horizontal axis, and the receiver is located on the Earth’s surface. Other measurement schemes are considered, in which the ionosphere is located on the signal path between the transmitter and the receiver. Previously, the authors performed a numerical simulation of the influence of the rotation of the polarization vector in the ionospheric plasma on radio waves of a higher, decimeter range. The relevance of these studies was associated with the creation of a space P-band synthetic aperture radar (SAR) for ground and subsurface remote sensing of the Earth, as well as with the problems of reconstructing the electron density profile of the ionospheric plasma by radio tomography methods. A comparison is made of the results of modeling the polarization characteristics of the decameter and decimeter ranges.