Monte Carlo Simulation of Light Propagation Through the Troposphere for Free Space Optical Communication

Monte Carlo simulation is a stochastic technique used to solve a variety of physical problems. In all applications of the Monte Carlo method, a stochastic model is constructed in which the expected value of a certain random variable is equivalent to the value of a physical quantity to be determined. In this paper Monte Carlo simulations were carried out for light propagation through the atmosphere at wavelength 0.785 mum which is chosen to fall inside transmission windows within the atmospheric absorption spectra. The simulation is based on the random walks that photons make as they travel through the atmosphere, which are chosen by statistically sampling the probability distributions for step size and angular deflection per scattering event. After propagating many photons, the net distribution of all the photon paths yields an accurate approximation to reality. There are some types of weather of the atmosphere that are chosen at which the simulation is held to determine the effect on the propagation of light. Several optical thicknesses were examined between 0.1 and 5, relevant to real atmospheric conditions. Results indicate that the heavy rain or a dense fog will completely stop the passage of optical-frequency radio waves through the troposphere. Therefore optical frequency radio waves will be used only in localities where the atmospheric precipitations are a rare occurrence