Scintillation Theory Revisited reviewed The Theory of Scintillation… as part of the broader theory of wave propagation in inhomogeneous media. In this framework, an electromagnetic (EM) field is separated into transverse field components and components that vary along the direction of propagation.
The classic example is propagation through a transparent, inhomogeneous medium. Any such propagating field can be represented as a sum of propagating plane waves with wave vectors defined by transverse and axial components. Forward propagation relies on one critical assumption, namely that any backward-propagating field initiated by forward propagation is negligible. It follows that the field in any plane fully determines the field beyond that plane. A forward-marching solution can be constructed by incrementally propagating the field forward.
The forward propagation assumption leads naturally to propagation equations that describe the field as it advances through the medium. Scintillation Theory Revisited established constraints that limit the application of the forward-propagation equation (FPE), which underlies all the analysis in The Theory of Scintillation…
Extensions of the theory beyond the FPE involve the implementation of complex operators that act on an inhomogeneous continuous medium. Planar boundaries are the only exception. No successful attempt has been made to generate analytic representations of statistical measures akin to the statistical theory of scintillation. However, realizations of continuously inhomogeneous, e. g. striated, media have been used to define a medium of interest.
At the present time the only viable means of studying the effects of propagation in irregular refractive media are simulations. This has carried over to applications of the FPE under the constrained conditions it is applicable, effectively all trans-ionospheric propagation involving near-line-of-sight propagation paths.
In Phase Screen Theory Revisited we review the phase-screen theory, its theoretical foundations, and extensions. The extensions refer to using multiple phase screen (MPS) simulations effectively to test phase-screen equivalence. A phase screen is mathematical abstraction, which is understood to be an equivalent operation that separates propagation and media where it is permissible to do so. The development reviews material from two recent publications On Phase Screen Models for Scintillation Diagnostics and Extreme Scintillation Structure Diagnostics. The papers introduce and demonstrate a new application of back propagation to reconstruct an equivalent phase screen. Iterative parameter estimation (IPE) is applied to the measured phase spectral density function (SDF) to estimate inverse-power-law structure parameters.