Wave propagation over extended atmospheric paths

Abstract

This chapter examines the behavior of infinitely extensive plane waves as they propagate over extended atmospheric paths. The analysis draws on results from the previous chapter for scattering by thin atmospheric layers. Using a coherency matrix approach for the refractive index field, the crucial result is established that extended atmospheric paths can be represented by finite stacks of statistically independent random phase screens. By analytically propagating light waves through these stacks, expressions are developed for the atmospheric MTF and the two-point two-wavelength correlation function of the complex amplitudes of the waves that emerge from the stacks. The expressions are given in terms of the rms OPD fluctuation over the path, σ, and the autocorrelation function of that fluctuation, qðn; gÞ. These two measures provide the essential statistical information about turbulence structure in the path. They also provide the essential statistical properties of the complex amplitudes and intensities in images formed by telescopes observing over the path.