• irradiance
• atmosphere

In recent years, an increasing interest has been raised around the application to satellite and space communications in general of the Optical Wireless Communication (OWC) Technology. The main driver of this interest is the ever growing demand for increase in data and multimedia services that has led to congestion in conventionally used radio frequency spectrum. Optical Wireless communication is the technology that uses optical carrier to transfer information from one point to another through an unguided channel which may be an atmosphere or free space.
Earth’s atmosphere is the channel medium in many applicative scenarios involving a Satellite-to-Earth or Earth-to-Satellite free space optical links. This medium impairs the propagation of the electromagnetic fields in a number of ways, especially in the layer up to 20 km above the Earth’s surface. This may be a source of loss of optical signal and limit link distance.
Among the main impairments, the most important, which will be studied in this work, is the atmospheric turbulence; it is a random phenomenon caused by variations in temperature and pressure of the atmosphere and it is characterized by the formation of turbulent cells and random changes in the refractive index. An important effect of this phenomenon is called scintillation and it leads to a redistribution of the signal energy caused by temporal and spatial fluctuations of the signal. From the point of view of the electromagnetic problem, such a channel medium can be studied with the theory of propagation in random media. Under this theory, the value of optical irradiance at a specific point in space is not a deterministic value, but is represented by a statistical distribution. Starting from the 1960s, an important research topic was the derivation of analytical forms of statistical distributions assumed by the optical irradiance, under different turbulence conditions.
The purpose of this work is to implement a numerical algorithm for the propagation of an optical field in turbulent atmosphere, derive the statistical distributions of the irradiance profile in a number of relevant cases and under different turbulence conditions, and compare them with some of the most classical theoretical PDFs that were proposed in literature. The developed algorithm makes use of the phase screens, a well established numerical technique employed to model in a calculator the impact on an optical wavefront of the continuous random variations of a turbulent medium.