Abstract: A study of the effect of various atmospheric conditions on a free-space optical communications link is undertaken. A field study was conducted near the Lancaster County Airport, Lititz, Pa., between March and September 1989, and confirmed the theory presented. Two systems were installed. The first system, an Ethernet system, had an optical link distance of 0.98 km. During 76.67 days of testing the overall system error free availability was 96.979 percent. The limiting factor was visibility in fog with an availability of 93.287 percent. Rain had little effect with an availability of 99.882 percent. The second system, a T1/DS1 telecommunications system, had an optical link distance of 0.93 km. During 122.29 days of testing the overall system error free availability was 98.550 percent. The limiting factor was visibility in fog with an availability of 94.277 percent. Rain had little effect with an availability of 99.998 percent. With the material presented the availability of any such optical link can be predicted.!
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