Optical propagation modelling using Radiative Transfer Equation (RTE)

Optical propagation characterization has been studied using the Radiative Transfer Equation (RTE) and RTE has been established as an accurate method for calculating optical attenuation of light propagating through inhomogeneous media. The RTE accounts for both the absorption and multiple scattering effects of light propagating through the atmosphere. The RTEs can be solved using numerical methods and are thus mathematically less challenging than the Maxwell equations which need analytical solutions. In this paper, the solution of RTE particularly through the realistic inhomogeneous cloud layers has been specifically addressed. The Monte Carlo approach has been applied to simulate photon trajectories propagating through the cloud layers from the optical transmitter to the receiver end. The wavelength dependence of optical attenuation through clouds has been studied in depth. The radiative transfer theory can be applied to explain the intensity fluctuations through the multiple scattering media. Results are being provided for the extinction (scattering and absorption) of photons through their interaction with water droplets in the cloud layers at laser wavelengths of 2 μm and 10 μm. The results on these specific wavelengths shall help the choice of lasers for optical links through the clouds.