The impact of liquid water content on free space optical propagation

Free space optical (FSO) technologies are providing recently an alternative solution for high speed data transmission against the common radio wave devices. Commercial systems are available on the market to transmit data even with the rate of Gbit/sec or higher. The applications are mainly designed for terrestrial line of sight operation at the length of few kilometres. By comparing it to the radio propagation, free space optics has different characteristics. Furthermore, the number of available channel models is also slight. As long as measurement devices to determine the main physical parameters for radio propagation (received power, precipitation sensors, etc.) are available and already standardized, for the optical propagation the sensors are often missing, non standardized or quite expensive. New models to characterize the FSO propagation, determine the main cause of the significant channel impairment factors are necessary to support the system engineers during the system design processes. In this contribution we study the dependency of the free space optical propagation on the air liquid water content (LWC). We will provide measurement results and a model to express the relationship between free space optical attenuation and liquid water content. This work is carried out under the cooperation between BME and IAP.