Two-scale solutions for intensity fluctuations in strong scattering

An exact integrodifferential equation is derived for a certain transform of the four-point coherence function by using a two-scale embedding procedure. The solution is expanded in an asymptotic series in the inverse strongscattering parameter, the terms of which are solutions of a hierarchy of simple first-order partial differential equations. Further approximations simplify the retransformation and display the four-point coherence in a useful, numerically convenient form. Results compare favorably with existing numerical computations of the scintillation index and the covariance in two-dimensional plane-wave propagation. Results for three-dimensional plane-wave propagation are also presented.