SIMPLE MATHEMATICAL-MODELS FOR TEMPORAL, SPATIAL, ANGULAR, AND ATTENUATION CHARACTERISTICS OF LIGHT PROPAGATING THROUGH THE ATMOSPHERE FOR SPACE OPTICAL COMMUNICATION - MONTE-CARLO SIMULATIONS

Mathematical models are developed to characterize propagation through a turbid medium at three different wavelengths in the visible and near infrared spectral range. These models are based upon relations betwee n the temporal, angular, and spatial spread of electromagnetic unpolar ized radiation, geometrical path length, particle size distribution, a nd the medium's propagation parameters such as Mie scattering, and abs orption coefficients, Mie phase-function, and optical thickness. Calcu lations of the radiation characteristics were carried out using Monte Carlo simulations. Here, atmospheric particulates are used to model tu rbid media for optical thickness between 1 and 6, emphasizing optical communication applications, The advantage of this work is the ability to predict simply and in real time important radiation parameters rele vant to any optical communication system. Results indicate very high c orrelation between optical thickness and propagation characteristics. For transmission, comparison is made to Bucher's model. Results are si milar except for absorption effects which are not included in Bucher's model. Some important conclusions are derived such as the prediction that it is advantageous to use longer wavelength radiation through the atmosphere. In addition, there is a very dominant back scattering eff ect, involving up to 50% of transmitted power for optical densities as low as 6. On the other hand, power density of received scattered ligh t is very low for conventional distances relevant to satellite optical communication, and can be neglected. On the basis of simulation resul ts, the received radiation is of unscattered light only for any optica l communication application. The dominant mechanism relating to radiat ion attenuation is scattering rather than absorption.