Chapter 13 - Scintillation theory

Abstract

Ionospheric turbulence can result in irregular structure that has a far-reaching impact on the propagation of electromagnetic waves. In particular, such irregularities can cause scintillation or rapid fading in amplitude and phase that disrupts satellite navigation systems and also degrades astronomical observations (the twinkle in stars). Consequently, the study of propagation through irregularities is important for understanding the performance of important sensing and communications systems. Unfortunately, such structure is far too complex to be usefully described in deterministic terms and a statistical description is the only practical alternative. The major problem is that of relating the statistics of the irregularities to the statistics of the propagating field. In the first part of this chapter we look at some traditional approaches to this problem, starting with the Born approximation. The Born approximation considers the irregularities that consist of a small perturbation to a background medium. The range of applicability of this approach can be extended through the Rytov approximation, but both techniques break down in strong turbulence. The latter part of the chapter concentrates on the use of multiple phase screens to simulate propagation through an extended medium. MPS techniques are valid for all levels of turbulence. Several numerical examples are included to demonstrate the utility of this approach.