Book contents
- Frontmatter
- Contents
- Preface
- 1 Introduction
- 2 Waves in Random Media
- 3 Geometrical Optics Expressions
- 4 The Single-path Phase Variance
- 5 The Phase Structure Function
- 6 The Temporal Variation of Phase
- 7 Angle-of-arrival Fluctuations
- 8 Phase Distributions
- 9 Field-strength Moments
- Appendix A Glossary of Symbols
- Appendix B Integrals of Elementary Functions
- Appendix C Integrals of Gaussian Functions
- Appendix D Bessel Functions
- Appendix E Probability Distributions
- Appendix F Delta Functions
- Appendix G Kummer Functions
- Appendix H Hypergeometric Functions
- Appendix I Aperture Averaging
- Appendix J Vector Relations
- Appendix K The Gamma Function
- Author Index
- Subject Index
1 - Introduction
Published online by Cambridge University Press: 14 January 2010
- Frontmatter
- Contents
- Preface
- 1 Introduction
- 2 Waves in Random Media
- 3 Geometrical Optics Expressions
- 4 The Single-path Phase Variance
- 5 The Phase Structure Function
- 6 The Temporal Variation of Phase
- 7 Angle-of-arrival Fluctuations
- 8 Phase Distributions
- 9 Field-strength Moments
- Appendix A Glossary of Symbols
- Appendix B Integrals of Elementary Functions
- Appendix C Integrals of Gaussian Functions
- Appendix D Bessel Functions
- Appendix E Probability Distributions
- Appendix F Delta Functions
- Appendix G Kummer Functions
- Appendix H Hypergeometric Functions
- Appendix I Aperture Averaging
- Appendix J Vector Relations
- Appendix K The Gamma Function
- Author Index
- Subject Index
Summary
The laws of geometrical optics were known from experiments long before the electromagnetic theory of light was established [1]. Today we recognize that they constitute an approximate solution for Maxwell's field equations. This solution describes the propagation of light and radio waves in media that change gradually with position [2]. The wavelength is taken to be zero in this approximation and diffraction effects are completely ignored. The field is represented by signals that travel along ray paths connecting the transmitter and receiver. In most applications these rays can be approximated by straight lines. These trajectories are uniquely determined by the dielectric constant of the medium and by the antenna pattern of the transmitter. In this approach energy flows along these ray paths and the signal acts locally like a plane wave. Geometrical optics provides a convenient description for a wide class of propagation problems when certain conditions are met.
The assumption that the medium changes gradually means that geometrical optics cannot describe the scattering by objects of dimensions comparable to a wavelength. Similarly, it cannot describe the boundary region of the shadows cast by sharp edges. A further condition is that rays launched by the transmitter must not converge too sharply – as they do for focused beams. These conditions must be refined when ray theory is used to describe propagation in random media.
Geometrical optics is widely used to describe electromagnetic propagation in the nominal atmosphere of the earth, other planets and the interstellar medium.
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- Information
- Electromagnetic Scintillation , pp. 1 - 4Publisher: Cambridge University PressPrint publication year: 2001