Estimation of Rain Attenuation in FSO Links based on Visibility Measurements

Rain affects FSO links even where fog occurrence is not low. However, rain has a major impact on FSO performance in locations where fog occurrence is statistically not relevant. The classical modeling of specific attenuation due to rain relies on the knowledge of rain statistics or measurements of raindrop size distribution. This contribution proposes a new wavelength- independent method to estimate rain attenuation based on visibility measurements under rainy conditions for FSO links. As input, a long-term database of surface records is considered, and four locations with different climate conditions are studied: Taipei, Taiwan, with a subtropical climate; Kuala Lumpur, Malaysia, with equatorial climate and characterized by tropical rain-forests; Rio de Janeiro, Brazil, with a tropical climate; and Milan, Italy, with a mid-latitude climate. The results obtained by the V-based model agree with the bounds retrieved from microphysical models.