Laser attenuation by falling snow

The effect of snow on a FSO link is here addressed both theoretically and experimentally. Data collected during the snowfalls occurred in Milan, Italy, in the winter time of 2005 and 2006 are presented and discussed. It is shown that attenuation due to snow is not at all negligible because it could largely exceed the one caused by heavy rainstorms. Further, as in the case of rain events, the use of a visibility sensor is not appropriate to infer the correct fade levels experienced by the laser beam.