DETERMINING THE ELECTROMAGNETIC PARAMETERS OF SOIL

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Context of the problem

Although the coverage offered by modern communication systems (cellular telephones, Wi- Fi, satellite, etc.) expands on nearly a daily basis, there are still instances where traditional High Frequency radio (HF, 3 to 30 MHz) ground wave and skywave communications are viable and cost effective alternatives. Examples include the aftermath of natural disasters such as earthquakes, tsunamis, tornadoes, floods, mudslides, etc. or man-made tragedies such as terrorist attacks. Under these circumstances, networks may become overloaded or the infrastructure severely damaged, reducing the capabilities of the network (Witvliet, 2015, pp. 2–3).
This can especially be problematic in lesser-developed countries where back-up networks may be less common or capable (Coetzee, 2004; McNamara, 1991, pp. 2–3). Furthermore, short-range skywave communications are for security reasons preferable to using the local cellular network in many tactical military deployments. During peacekeeping missions in a foreign country, unlawful elements may have access to cellular networks, thus potentially compromising any operations. A good example of where HF systems can be useful is when a group needs to operate deep in a remote ravine where the geography may negatively influence the commonly used line- of-sight communication channels such as Very High Frequency (VHF) radio or cellular signals and an alternative communications mode needs to be utilised. Distances involved are typically short in terms of how the crow flies, but the terrain may be very challenging. Under these circumstances, Near Vertical Incidence Skywave (NVIS) communications as depicted in Figure 1.1 are very effective (Goodman, 1992, p. 218).
The high take-off angle for NVIS communications is quite the opposite of long distance HF communications where low radiation angles are typically required (Goodman, 1992, p. 222; Witvliet et al., 2015). A HF signal can propagate via various mechanisms between a transmitting and a receiving station. The space wave consists of all the signals that may reach a receiver under line-of- sight conditions. This is also referred to as the direct signal (Goodman, 1992, pp. 182, 183).
The space wave and surface wave are collectively referred to as ground wave propagation (DeMinco, 1999). (Ground wave propagation is discussed in Chapter 3.) Propagation via ionospheric refraction and reflection is referred to as skywave propagation and is discussed in Chapter 5. The ground wave component of the HF wave can provide unique capability for communications and is important in a variety of military applications as well (Goodman, 1992, p. 184). It is strongly affected by the environment and must be accurately modelled to predict tactical communications performance including interference from jamming sources, and to predict communications in difficult geographical environments such as built-up, forested and mountainous terrain (Hill, 1982). Ground wave propagation is also utilised for commercial broadcast beyond line-of-sight (LOS) (Davila, 1993). Central to successful HF communications is the ability to accurately determine the electromagnetic properties of the ground for the operational frequency. The electromagnetic properties of ground define the path loss of ground wave communications as well as the performance (radiation angle and gain) of an antenna located close to the surface of the earth (in terms of wavelength) that is used for skywave propagation via the ionosphere (IEEE Std 356, 2011, p. 1; Goodman, 1992, p. 192). For successful skywave communications, a sound knowledge of ionospheric propagation is essential.
Fortunately, there are many modern computer programs available that can predict optimum frequencies and guide antenna choices. Examples include the Voice of America Coverage Program (VOACAP), adopted from the Ionospheric Communications Analysis and Prediction Program (IONCAP) (Teters et al., 1983) and the Ionospheric Communications Enhanced Profile Analysis and Circuit Prediction Program (ICEPAC), also a descendant of IONCAP (Tascione et al., 1987). DX Atlas and HamCap make use of the VOACAP engine to predict propagation conditions on a global scale. These two programs can download real-time space weather conditions from the Internet via the IonoProbe utility. Another option is Proplab-Pro, which was developed by Solar Terrestrial Dispatch (Alberta, USA). Proplab-Pro Version 3 uses the 2007 version of the International Reference Ionosphere (IRI) (Bilitza, 2001).
It makes use of advanced two-dimensional and three- dimensional ray-tracing algorithms. The Advanced Stand Alone Prediction System (ASAPS) is based on an ionospheric model developed by Space Weather Services within the Australian Bureau of Meteorology and the International Telecommunication Union Radiocommunication Sector (ITU-R)/Comité Consultatif International pour la Radio, Consultative Committee on International Radio (CCIR) models (ITU-R Rec.P533-10; ITU- R Rec.P372-10 and CCIR Report 322). A global network of near real-time ionospheric sounders (known as ionosondes) ensures that the data used by some of these prediction programs are accurate and current, contributing to the usefulness of the results (Frissell et al., 2014).

TABLE OF CONTENTS :

• CHAPTER 1 INTRODUCTION
  • 1.1 PROBLEM STATEMENT
    • 1.1.1 Context of the problem
    • 1.1.2 Research gap
  • 1.2 RESEARCH OBJECTIVES AND QUESTIONS
  • 1.3 APPROACH
  • 1.4 RESEARCH GOALS
  • 1.5 RESEARCH CONTRIBUTION
  • 1.6 OVERVIEW OF STUDY
• CHAPTER 2 DETERMINING THE ELECTROMAGNETIC PARAMETERS OF SOIL
  • 2.1 INTRODUCTION
  • 2.2 GROUND PARAMETERS PUBLISHED BY THE ITU
  • 2.3 BACKGROUND
  • 2.4 UNIVERSAL RC NETWORK SOIL MODEL
  • 2.5 DETERMINING THE MOISTURE CONTENT OF SOIL
  • 2.6 CONFIRMING THE CALCULATED ELECTROMAGNETIC PARAMETERS OF SOIL
  • 2.7 SUMMARY
• CHAPTER 3 VALIDATING THE SOIL MOISTURE TECHNIQUE BY MEANS OF HF GROUND WAVE PROPAGATION
  • 3.1 INTRODUCTION
  • 3.2 GROUND WAVE PROPAGATION
  • 3.3 BACKGROUND
  • 3.4 GRWAVE
    • 3.4.1 The GRWAVE computer model
    • 3.4.2 GRWAVE input parameters
  • 3.5 USING GRWAVE TO VALIDATE THE CALCULATED SOIL PARAMETERS
  • 3.6 SUMMARY
• CHAPTER 4 DEDUCING THE ELECTROMAGNETIC PROPERTIES OF SOIL USING AN INTERFEROMETRIC DF AND GROUND WAVE TILT
  • 4.1 INTRODUCTION
  • 4.2 WAVE TILT
  • 4.3 WAVE TILT THEORY
    • 4.3.1 Expected wave tilt values
  • 4.4 INTERFEROMETRIC DIRECTION FINDING PRINCIPLES
  • 4.5 THE GEW TECHNOLOGIES MRD5000 WIDEBAND HF INTERFEROMETRIC DIRECTION FINDER
  • 4.6 WAVE TILT MEASUREMENTS WITH AN INTERFEROMETRIC DIRECTION FINDER
  • 4.7 POSSIBLE FUTURE WAVE TILT WORK
  • 4.8 DISCUSSION AND SUMMARY
• CHAPTER 5 PRINCIPLES OF HF IONOSPHERIC PROPAGATION
  • 5.1 INTRODUCTION
  • 5.2 BACKGROUND
  • 5.3 THE IONOSPHERE
  • 5.4 CHARACTERISING THE IONOSPHERE
  • 5.5 HF SKYWAVE PROPAGATION
  • 5.6 SUMMARY
• CHAPTER 6 SINGLE SITE LOCATION PERFORMANCE
  • 6.1 INTRODUCTION
  • 6.2 BACKGROUND
  • 6.3 SINGLE SITE LOCATION PRINCIPLES
  • 6.4 ASSIGNING A QUALITY FACTOR TO THE CALCULATED SSL DISTANCES
  • 6.5 VALIDATION
  • 6.6 POSSIBLE FUTURE WORK
  • 6.7 DISCUSSION AND SUMMARY
• CHAPTER 7 CONCLUSION
• • REFERENCES
  • ADDENDUM A SSL RESULTS FOR TWO CIRCUITS

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