For example,
with sufficient link margins, FSO systems are immune to weather conditions that are
detrimental to signal propagation. The amount of link margin needed depends on the
distance of the communication link and the weather condition against which immunity
is sought.
Weather The effect of weather on optical wireless is very well understood. Weather
can produce conditions that can affect the propagation of the optical signal through the
atmosphere. These weather conditions include fog, haze, rain, and snow. The net effect
of any one of these weather conditions on an FSO link is the reduction (or loss) of the
total amount of received optical power.
244 Chapter 9
The loss in received optical power due to a weather condition is expressed in terms of
dB and is computed as 10 times the Log of the factor by which the received optical power
is reduced. The loss of an optical signal due to weather conditions has been well studied.
Table 9.1 provides a list of various weather conditions and the loss caused per km on
a typical optical wireless signal. Loss at other distances can be derived simply by multiplying
the loss per km listed in the table by the desired distance in km.
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