Long Distance Propagation of HF Radio Waves: (12 Physics and Chemistry in Space)

The study of very long-distance and around-the-world propagation of HF radio waves becomes more urgent in connection with the problems of long- distance ground-based radio communications, communications with space- crafts and satellites, satellite-to-satellite communications, around-the-world radar scanning, around-the-world sounding of the ionosphere, etc. At pre- sent, these investigations have acquired particular interest because transmit- ters which make it possible to intentionally modify the ionospheric properties by powerful radio waves have become available. In the case of radio wave propagation over comparatively small distances (about 3000 - 5000 km, one - two hops), in a first approximation, the iono- sphere can be considered homogeneous in the horizontal direction. The radio wave propagation theory in a horizontally-homogeneous, i. e. , spherically- symmetric ionosphere was developed with sufficient completeness as early as in the 1920-1940's by Appleton, Ratcliffe, Beynon, Booker, Martyn, and others. This theory is presented in detail in the well-known monographs by Ginzburg (1967), Bremmer (1946), and Budden (1961). Based on this theory, detailed methods for the calculation of radio paths, determination of field amplitude, and interpretation of vertical and oblique ionograms have been developed. All these methods are well-known and widely used in practice, see monographs by Al'pert (1974), Shchukin (1940), and Davies (1969). An altogether different situation takes place in the case of very long-dis- tance multihop and around-the-world propagation.

Table of Contents:
1 Introduction.- 1.1 Very Long-Distance and Magnetospheric Propagation.- 1.1.1 Round-the-World Signals.- 1.1.2 Long-Distance Oblique Sounding.- 1.1.3 Magnetospheric Propagation.- 1.2 Features of Radio Wave Propagation over Long Distances.- 2 Spherically-Symmetric Ionosphere.- 2.1 Wave Equation in the Spherically-Symmetric Ionosphere; Ionospheric Wave Ducts.- 2.2 Radio Wave Field in an Ionospheric Duct.- 2.3 Radio Wave Tunneling through the Interduct Barriers; Capture Coefficient.- 2.4 Ray Trajectories; Pulse Propagation.- 3 Horizontally-Inhomogeneous Ionosphere.- 3.1 Geometrical Optics.- 3.2 Adiabatic Approximation.- 3.3 Lateral Deviations of the Radio Wave Trajectories; Bearing Variation.- 3.4 Capture of Radio Waves into the Interlayer Ionospheric Duct and Their Escape from the Duct.- 4 Regularities of Very Long-Distance Radio Wave Propagation in the Ionosphere.- 4.1 Investigations of the Global Characteristics of Long-Distance Propagation.- 4.2 Radio Wave Absorption.- 5 Calculation of Long-Distance Radio Paths.- 5.1 Radio Path Calculation with a Parabolic Model of the Ionosphere.- 5.2 Calculation of Long-Distance Radio Paths, Using the Complex Ionospheric Model.- 5.3 Comparison of the Adiabatic Approximation with the Ray-Tracing Techniques.- 6 Radio Wave Scattering.- 6.1 Effect of Scattering on the Capture of Radio Waves into the Interlayer Duct.- 6.2 Effect of Multiple Scattering on Radio Wave Propagation in a Duct.- 6.3 Signal Fluctuations in the Reception Point.- 7 Nonlinear Phenomena.- 7.1 Regular Nonlinear Refraction.- 7.2 Nonlinear Radio Wave Scattering.- 7.2.1 Character of Irregular Plasma Density Perturbations.- 7.2.2 Influence of Nonlinear Scattering on Radio Wave Capture into IWD and Departure from the Duct.- 7.2.3 Effect of Nonlinear Scattering on Long-Distance Radio Propagation.- 8 Radio Wave Propagation in the Magnetosphere.- 8.1 Electromagnetic Wave Guiding by Weak Waveguides.- 8.2 HF Radio Waves in the Magnetospheric Ducts.- Appendix 1 Wave Equation. Radio Wave Field Distribution in Connected Waveguide Ducts.- A1.1 Wave Equation.- A1.2 Radio Wave Field Distribution in Connected Waveguide Ducts.- Appendix 2 Analytical Models of Ionospheric Parameters.- A2.1 Three-Dimensional Equinoctial Model of Electron Density in the Ionosphere.- A2.2 Three-Dimensional Equinoctial Model of Electron Effective Collision Frequency.- Appendix 3 Wave Theory of HF Radio Wave Propagation in a Horizontally-Inhomogeneous Ionosphere (N. D. Borisov and A.V. Gurevich).- A3.1 Wave Propagation in a Slightly Inhomogeneous Ionosphere.- A3.2 Quasispherical Approximation.- A3.3 Interaction of Quasispherical Modes in the Real Ionosphere.- A3.4 Adiabatic Modes of Ionospheric Waveguides.- A3.5 Radio Wave Capture into IWD.- A3.5.1 Neighborhood of the Separatrix.- A3.5.2 Antenna Radiation Field.- A3.5.3 Radio Wave Capture into a Duct. Role of Wave Effects.- Principal Symbols.- List of Abbreviations.- References.