Ionospheric Radio
This book is aimed at professional scientists, engineers and students who need an intermediate-level reference and/or text. Students of aeronomy and radio wave propagation are introduced to basic wave theory in absorbing, anisotropic and dispersive media and to the physics of production, loss, and movement of plasma in the ionosphere presence of the geomagnetic field.
Inspec keywords: magnetosphere; ionospheric disturbances; solar-terrestrial relationships; ionospheric electromagnetic wave propagation
Other keywords: magnetoionic theory; radio soundings; ionospheric radio; onosphere morphology; high-frequency propagation predictions; wave characteristics; extremely low frequency; ionospheric disturbances; ionospheric modification; radio communication; oblique propagation; solar-terrestrial relationships; earth-space propagation; plasma characteristics
Subjects: Radiowave and rocket soundings of the ionosphere; Interaction between ionosphere and magnetosphere; Ionospheric plasma waves, instabilities, and interactions; Plasmasphere and plasmapause; Ionospheric electromagnetic wave propagation; Ionospheric disturbances and modification experiments
- Book DOI: 10.1049/PBEW031E
- Chapter DOI: 10.1049/PBEW031E
- ISBN: 9780863411861
- e-ISBN: 9781849193870
- Page count: 600
- Format: PDF
-
Front Matter
- + Show details - Hide details
-
p.
(1)
-
1 Characteristics of waves andplasmas
- + Show details - Hide details
-
p.
1
–26
(26)
In this chapter, the following characteristics of waves and plasmas in ionosphere are discussed. (1) Plane waves. (2) Propagation in a dispersive medium. (3) Propagation in an anisotropic medium. (4) Wave packets. (5) Phase paths and packet paths. (6) Electromagnetic waves. (7) Plasma frequencies. (8) Gryrofrequencies. (9) The Debye length and (10) Motions of ions in crossed electric and magnetic fields.
-
2 Solar-terrestrial relationships
- + Show details - Hide details
-
p.
27
–69
(43)
The Earth's upper atmosphere is ionized by radiations, both electromagnetic and corpuscular, from the Sun. The electromagnetic radiations, such as radio, infrared, visible, ultraviolet, extreme ultraviolet, and X-rays, travel directly between Sun and Earth at the free space speed with a transit time of about 8-3 minutes. The region between and including Sun and Earth has these components: the Sun, the interplanetary medium, the Earth's magnetosphere, the Earth's neutral atmosphere, and the Earth's ionosphere as depicted in Fig. 2.1. Understanding the features of the solar-terrestrial system discussed in this Chapter is essential to an understanding of the spatial and temporal structure of the ionosphere.
-
3 Magnetoionic theory
- + Show details - Hide details
-
p.
70
–88
(19)
This book chapter presents a discussion of magnetoionic theory in relation to radiowave propagation in the ionosphere. It begins with the Appleton formula, its properties, and approximations followed by radiowave polarization theory including ordinary-extraordinary wave coupling. Ray direction in a magnetoplasma is also discussed as well as effects of heavy ions. Finally, the chapter closes with the generalization of magnetoionic theory.
-
4 Radio soundings of the ionosphere
- + Show details - Hide details
-
p.
89
–123
(35)
Most of our knowledge of the ionosphere comes from remote sensing by radio waves. Single-frequency techniques for remotely measuring time of flight, amplitude, phase, polarization, and angles of arrival include reflection by refractive bending and by so-called coherent and incoherent scatter. The sweep frequency ionosonde technique was developed to probe the vertical structure of the ionosphere. Moving transmitters and/or receivers (on satellites) have been used to investigate the horizontal structure of the ionosphere. We discuss some of these techniques later in this chapter but first we consider the principles underlying the measurement of wave features.
-
5 Morphology of the ionosphere
- + Show details - Hide details
-
p.
124
–154
(31)
This chapter presents a discussion on the morphology of the ionosphere. It begins with the analysis of synoptic variations in the ionosphere together with the spatiotemporal variations of the critical frequency of its individual layers. Models for the ionospheric layers are also dealt with including the D region and the sporadic E and spread F layers. Finally, electron and ion temperature structures of the ionosphere are discussed.
-
6 Oblique propagation
- + Show details - Hide details
-
p.
155
–207
(53)
Although vertical soundings are of great value in the study of ionospheric structure and dynamics, radio users are concerned with oblique propagation, e.g. point-to-point, broadcasting, and surveillance. In this chapter we concern ourselves with the applications of vertical data to problems encountered in oblique propagation, e.g. with methods of calculating maximum usable frequencies and with identification of echo structures.
-
7 Amplitude and phase
- + Show details - Hide details
-
p.
208
–259
(52)
This chapter deals with the effects of ionospheric propagation on a radio signal's amplitude and phase structure. Radio signal attenuation in terms of losses e.g. power loss and spatial losses are discussed together with ionospheric absorption and its temporal and spatial variations. Polarization matching and fading are also included. Radio signal frequency in relation to its phase is also given focus. Ionospheric drifts, traveling ionospheric disturbances, acoustic-gravity waves, and nonreciprocal phenomena are also discussed.
-
8 Earth-space propagation
- + Show details - Hide details
-
p.
260
–311
(52)
This chapter discusses the use of satellite sounders to study the topside ionosphere and then considers the use of fixed-frequency transmissions to study total electron content (TEC) and irregularities, and the reverse, namely, the effects of ionospheric electron content and irregularities on radio transmissions.
-
9 Ionospheric disturbances and their effects on radio communication
- + Show details - Hide details
-
p.
312
–366
(55)
This chapter deals with the effects of different ionospheric disturbances on radio communication. These disturbances include solar disturbances, sudden ionospheric disturbances, ionospheric storms, polar cap absorption (PCA) events, traveling ionospheric disturbances (large scale), and associated disturbances in the geomagnetic field (solar flare effect, SFE), aurora, and magnetospheric substorms. High latitude radio communications is also discussed. Finally, ionospheric forecasting and its accuracy is presented.
-
10 Low, very low, and extremely lowfrequencies
- + Show details - Hide details
-
p.
367
–408
(42)
This chapter deals with low-, very-low-, and extremely-low-frequency radiowave propagation in the ionosphere with particular focus on their phase and amplitude characteristics and variations. Ionospheric whistlers are also discussed.
-
11 Medium frequencies
- + Show details - Hide details
-
p.
409
–440
(32)
The medium-frequency band (300-3000 kHz) is dominated by the amplitude modulation (AM) broadcast band (≈ 500-1700 kHz). This frequency band has an enormous economic, social, and political impact on everyday life and it is intensively used. Although the MF band is an important part of the radio spectrum, our knowledge of propagation in the band is rather poor because of (i) spectrum congestion, (ii) high absorption, (iii) the complicated role of the Earth's magnetic field, (iv) difficulty in separating deviative from nondeviative effects, (v) collisions, and (vi) the fact that, on the lower frequencies, the medium is not slowly varying. For efficient use of the MF band it is essential for users to share the same channel with minimum interference. Thus the estimation of the signal strength in distant regions is an important consideration in channel sharing with potentially interfering transmitters. This chapter deals with midfrequency radiowave propagation in the ionosphere including skywave signal propagation and midfrequency broadcasting.
-
12 High-frequency propagationpredictions
- + Show details - Hide details
-
p.
441
–469
(29)
This chapter will give the reader a brief idea of the ways in which ionospheric data are applied to high-frequency communication problems. Several computer programs, available for both mainframe and personal computers, make it possible to determine optimum frequencies, signal strengths, broadcast coverages, and so forth. For the determination of required transmitter power, for a specified grade of service, maps of worldwide distribution of radio noise and its variability are available in CCIR (1988). Ionospheric predictions are useful in planning systems, selecting frequencies, and assessing interference (intentional and otherwise) between systems. They are valuable in the overall frequency management of the high-frequency band. Ionospheric data are of value to (i) short-term operators who have to react to circuit interruption because of MUF failure, high absorption, excessive fading, and (ii) long-term system planners and frequency managers who are involved with the installation of terminal equipment, antenna design, compatibility and cost. This chapter is concerned, primarily, with the second category. We also consider real-time channel assessment in which probing signals (e.g. oblique soundings) are used to evaluate the channel capacity. Such evaluations are of particular use to traffic controllers and circuit operators. We consider predictable characteristics, their temporal and spatial variabilities, some specific prediction systems, and applications to communications.
-
13 Propagation on very high frequencies
- + Show details - Hide details
-
p.
470
–505
(36)
The very-high-frequency range is defined as between 30 MHz and 300 MHz. The ionosphere can reflect radio signals on frequencies of > 50 MHz but over most of the VHF range the main effect of the ionosphere is to scatter radio energy by irregularities. Such irregularities exist in the D region (turbulence), in the E region (meteors and sporadic E), and in the F region, especially near the dip equator and in high latitudes (plasma instabilities). On lower frequencies (e.g. less than 50 MHz) propagation effects such as Faraday rotation, angular refraction, and time delay can be important. The value of Y(=fH/f) is small (<0.05), and under most conditions the propagation is essentially quasi-longitudinal (e.g. on 60 MHz for θ ≲ 89.28° with fH = 1.5 MHz) and the ray path is almost straight. The maximum electron densities in the ionosphere are rarely sufficient to reflect radio waves on frequencies much above 30 MHz except for relatively short periods (e.g. in the equatorial regions and in higher latitudes near the maximum of the sunspot cycle). For communications on the ground the main ionospheric mechanism is scattering by plasma irregularities. The chief irregularities in the ionosphere are: (i) turbulence in the D region; (ii) ionized trails due to the passage of meteors through the atmosphere; (iii) spread-F (field aligned); (iv) sporadic E; and (v) artificial irregularities. This chapter deals with very high frequency radiowave propagation in the ionosphere with particular focus on scattering phenomena including D-region scatter, meteorscatter, auroral scatter, and equatorial scatter. VHF propagation by ionospheric layers is also discussed.
-
14 Ionospheric modification
- + Show details - Hide details
-
p.
506
–537
(32)
The ionosphere can be affected (modified) by a variety of disturbances. Natural sources include, for example, severe weather, earthquakes, and volcanoes; these create mechanical disturbances (waves) in the neutral atmosphere which propagate to the ionosphere where they couple into the ionized gas. Anthropogenic disturbances include, for example, high explosives, nuclear explosions, heating by electromagnetic waves, and intentional and unintentional seeding of the ionosphere with chemicals.
-
15 Exercises
- + Show details - Hide details
-
p.
538
–552
(15)
This chapter presents problem exercises for ionospheric radiowave propagation theory.
-
Back Matter
- + Show details - Hide details
-
p.
553
(1)