Vol 69, No 6 (2024)

New methods for diagnostics of the fine structure of the Earth’s ionosphere and their verification by comparing the results of their application with the results of modeling and independent direct measurements are presented. Techniques for reconstructing the profiles of electron density and electron collision frequency in the ionosphere are developed using information on the polarization and amplitude characteristics of the ordinary and extraordinary components of the recorded signals with linear frequency modulation during vertical and oblique sounding. Mathematical and numerical modeling of the influence of ionospheric inhomogeneities on the propagation of short-wave radiation, as well as an analysis of temporal variations in the amplitude, polarization and trajectory characteristics of decameter radio signals reflected from the ionosphere, have been carried out. Based on the bicharacteristic method and the wave theory of catastrophes, methods for mathematical modeling of the features of the propagation of frequency-modulated radio signals in the ionospheric plasma in the presence of local inhomogeneities of the medium are developed. Numerical algorithms for programs for constructing ionograms of oblique and vertical sounding in the presence of local inhomogeneities in the ionosphere are developed.

Measurements of atmospheric absorption in transparency windows in the range of millimeter waves (MMW) have been carried out. A modification tipping-curve method is proposed that allows measuring atmospheric absorption, the average temperature of the atmosphere and separating the contributions of atmospheric moisture and the droplet fraction of clouds by single-wave measurements in the MMV range with clouds up to 2.5 points (without precipitation). The possibility of detecting and determining the water content of clouds at the zenith in real time is shown. The annual course of atmospheric moisture content and atmospheric absorption at a wavelength of 3 mm (2019 and 2020–2021) for the Karadag landfill. The previously obtained results of a comparative analysis of the Karadag landfill and the Suffa plateau are confirmed. The possibility of using the Karadag landfill for the installation of space communication systems and measurements of space sources in the MMV range is shown.

The field of a vertical electric dipole over a flat impedance surface is considered. Formulas for calculating the attenuation function of the ground wave field over real impedance underlying media are presented. The reduced surface impedance is determined at the boundary of the “ground-air” media and is expressed by the ratio of the tangential components of the electric and magnetic fields. For layered underlying media, the surface impedance is calculated using a recurrent formula that takes into account the thickness and electrical properties of each layer (dielectric constant and resistivity). The effects associated with the presence of a surface electromagnetic wave (SEW), when the electromagnetic field exhibits a clearly expressed surface character, are established. It is shown that the conditions for the propagation of long, medium and short radio waves over the “ice-sea” structure with a highly inductive impedance are more favorable than over an ideally conducting medium due to the occurrence of SEW.

The problem of nonlinear interaction of wave fields under conditions of saturable and threshold nonlinearity is considered. The possibility of existence of concentrated wave fields under these conditions is shown. A significant difference between the interaction of such fields and the interaction of classical solitons is observed. It is established that a certain ratio of nonlinearity parameters can lead to a significant increase in wave intensity.

The paper presents a new method for physical modeling of a multipath radio propagation environment with desired properties using a set of software-defined radio units. Using this method the authors conduct an experimental study on the convergence rate of a received multipath radio signal to a Gaussian random process as the number of multipath channel taps rises. The experiments showed that seven or less multipath taps are insufficient for accepting the statistical hypothesis of a Gaussian random process for the received signal, which revises previous theoretical studies. For the case of equal variances of all multipath taps the experiments verified the independence of the signal correlation function on the number of the taps. The obtained experimental data are fitted well to the classical theoretical models of multipath channels.

The possibility of increasing the accuracy of rainfall intensity retrieval based on space observations of atmospheric mesoscale convective complexes (MCC) is considered. It is shown that guaranteed detection of MCC requires complex observation of the Earth’s atmosphere in the IR and microwave ranges. The analysis showed that quasi-synchronous measurements from geostationary platforms in the IR range and observations from polar-orbital platforms in the microwave range are necessary to improve the retrieval accuracy. The method developed based on the analysis of MCC characteristics and capabilities of modern remote sensing satellite systems provides high time resolution of the MCC detection and monitoring system. The accuracy estimates of such quasi-synchronous measurements for currently existing sources of space information are obtained.

The features of recognition of hazardous weather phenomena associated with wind, and the problems arising in this case are considered. It describes a numerical experiment carried out to confirm the theoretical research of the effectiveness of the application for these purposes of a new parameter of the received signal - the bandwidth-duration product. On the basis of the obtained results the conclusion about the perspective of its application in weather radar is made.