FSO-Relevant New Measurement Results under Moderate Continental Fog Conditions at Graz and Milan

Interest in free space optics (FSO) has gained enormous popularity over the last few years, mainly due to two reasons, firstly delivering data rates that can meet future broadband telecommunication requirements and secondly as an alternate technology to solve the last mile access gap. However, optical signal transmitted in free space is subjected to deterioration while propagating due to its interactions with the particles of different sizes and shapes. The presence of hydrometeors in the atmosphere, for example, fog, mist, clouds, sleet, rain, snow and hail presents a very severe challenge to the optical signal propagation; especially fog leads to signal attenuations up to an order of few hundreds of dB/km. In this paper, the behaviour of FSO links installed in Milan and Graz in the presence of moderate continental fog conditions is analyzed analytically. Based on measurements made of signal attenuation at the two mentioned locations, comparisons are made for the peak, mean and median values of measured specific attenuation values and predicted signal attenuation values calculated analytically using standard modified gamma drop size distribution parameters and Mie scattering theory. Moreover, using Mie scattering theory a new set of modified gamma drop size distribution parameters are proposed for the measured peak, median and average values of specific attenuations for moderate continental fog conditions at Milan and Graz.