Evaluation of Fog Attenuation Results for OpticalWireless Links in Free Space

Fog presents the biggest challenge to propagation of optical signal in free space causing severe attenuations reaching up to several hundred of dB/km. In this paper, an overall fog attenuation behavior of the optical wireless links installed at Milan (Italy) and Graz (Austria) under moderate continental fog conditions, and Nice (France) under dense maritime fog environments is compared and evaluated based on the measured fog attenuations data. The attenuation data evaluated here of Graz and Milan consists of five and two winter months respectively, while for Nice it consists of eight summer days. It is shown that like any other meteorological effects, optical signal attenuations in different fog environments depends very much on the season, geographical location and on the time of the day. Based on the analysed data results for moderate fog environments, we infer that attenuations are particularly high during months of December, January and February, whereas, for dense maritime fog environments it depends additionally to some other meteorological parameters besides the geographical location and the time of the day. From this attenuation behavior analysis interesting results are obtained which can be helpful to understand the fog and its attenuations prediction behavior for optical signals transmitted in free space.