The Atmospheric Mutual Coherence Function from the First and Second Rytov Approximations and its Comparison to That of Strong Fluctuation Theory

TL;DR

This paper derives the mutual coherence function for electromagnetic beams in atmospheric turbulence using Rytov approximations and compares it to strong fluctuation theory, highlighting good agreement in weak fluctuations and instabilities in certain cases.

Contribution

It demonstrates that both first and second Rytov approximations are necessary and compares their results to strong fluctuation theory, revealing stability issues for beam wave intensities.

Findings

Good agreement between Rytov and strong fluctuation theory in weak turbulence.

Instabilities occur for beam wave intensities within the Rytov framework.

Identification of the source of instabilities related to amplitude treatment.

Abstract

An expression for the mutual coherence function (MCF) of an electromagnetic beam wave propagating through atmospheric turbulence is derived within the confines of the Rytov approximation. It is shown that both the first and second Rytov approximations are required. The Rytov MCF is then compared to that which issues from the parabolic equation method of strong fluctuation theory. The agreement is found to be quite good in the weak fluctuation case. However, an instability is observed for the special case of beam wave intensities. The source of the instabilities is identified to be the characteristic way beam wave amplitudes are treated within the Rytov method.