Splitting algorithms for paraxial and Itô-Schrödinger models of wave propagation in random media

Abstract

This paper introduces a full discretization procedure to solve wave beam propagation in random media modeled by a paraxial wave equation or an Itô-Schrödinger stochastic partial differential equation. This method bears similarities with the phase screen method used routinely to solve such problems. The main axis of propagation is discretized by a centered splitting scheme with step $\hat{I}”z$ while the transverse variables are treated by a spectral method after appropriate spatial truncation. The originality of our approach is its theoretical validity even when the typical wavelength $\hat{I}¸$ of the propagating signal satisfies $\hat{I}¸\ll \hat{I}”z$. More precisely, we obtain a convergence of order $\hat{I}”z$ in mean-square sense while the errors on statistical moments are of order $(\hat{I}”z{)}^2$ as expected for standard centered splitting schemes. This is a surprising result as splitting schemes typically do not converge when $\hat{I}”z$ is not the smallest scale of the problem. The analysis is based on equations satisfied by statistical moments in the Itô-Schrödinger case and on integral (Duhamel) expansions for the paraxial model. Several numerical simulations illustrate and confirm the theoretical findings.