Atmospheric turbulence profile modeling for satellite-ground laser communication

Abstract

The major limitation of free-space laser communications' performances is due to atmospheric turbulence. Free-space optical channels are characterized by a set of different parameters such as the scintillation index, the Rytov variance, the Fried parameter etc. These parameters stem from the particular atmospheric turbulence model chosen. These latter produce random temperature variations of the air which in turn induce random fluctuations of its refractive index. In order to design reliable ground-to-satellite optical communications links, vertical profiles modelings of the strength of refractive turbulence, i.e. the so-called C2n structure parameter are needed. Several of these models yet exist and depend on several factors and approximations (average profile, site dependent profile, night or daytime etc.). In the framework of this thesis, a study shall identify the statu-quo of atmospheric turbulence modelling (structure parameter, inner and outer scale profiles) options. The models shall be tested and assessed with respect to realism, applicability, advantages and drawbacks by calculation of particular channel parameters. The most promising one shall be identified and further developed as possible. 1. Literature research on profile modelling of structure parameter, inner and outer scale (the Hufnagel-Valley model is the most common one. However, quite often not very suitable). The models might be given in closed form, generic or numerically given for a particular ground station site. 2. Comparison of selected models with respect to applicability, realism, accuracy, needed input parameters (overview table / technical note). 3. Calculation of LEO-Ground channel parameters for selected models and comparison and discussion of results. -Rytov variance, scintillation index, intensity correlation width, Fried parameter etc. -Consideration of weak/moderate/strong fluctuation regime 4. Selection of most useful model. This model might be further developed if possible/necessary. 5. Comparison of results with actual measurements from ground station site Oberpfaffenhofen (optional, depends on work progress). Finally the expected outcome of this thesis is the following: -Comprehensive overview on modelling option of Cn2, inner and outer scale. -Demonstration of the effect of different models on the channel parameters (Rytov variance, scintillation index, intensity correlation width, Fried parameter). -Identification of the optimal model of Cn2, inner and outer scale for the LEO-ground link.