Quadratic structure functions and scintillation

Abstract

The quadratic structure function (QSF) approximation by itself does not imply a tilt-only medium in which log-amplitude fluctuations are absent. When the QSF is applied to the fourth-order coherence function, the signal variance has contributions from log-amplitude fluctuations and beam wander but not beam spreading. However, the use of the QSF in the log-amplitude correlation function is limited as it can result in increasing correlation functions for weak turbulence.