Approximate expression for the spherical wave structure function in a von-karman type random medium

We propose a relatively simple and convenient approximate expression for the spherical structure func-tion in atmospheric turbulence having the Von-Karman spectrum. The approximation, which is accurate to within 6%, is valid for any separation between the observation points. In the asymptotic intervals 2πρ<<l₀, l₀<<2πρ ((L₀, 2πρ))L₀ the approximate expression coincides with the known analytical solutions. An approximate expression is presented also for the coherence length ρ_o) for the case of homogeneous tur-bulence conditions along the propagation path.