Question

I think that it is probable the transmission distance to get shorter and the communication to get disturbed according to the weather condition. In the case of rain and snow the transmission distance seems to be able to be estimated based on the rainfall and the snowfall. But it is difficult for the fog to be estimated because it is indicated by the visibility. Would you please tell me the standard to be regulated for the fog ?

Answer

At first the definition of the visibility is now answered. The standard visibility is defined as the distance where the black object is discriminated from the other on the horizon in the sunshine in the uniform sphere.

But it is difficult to measure the visibility based on the definition and the visibility is generally converted from the result to be measured by the optical equipment. It is called MOR (Meteorological Optical Range) and is defined as the distance where the light is reduced to 5% after the transmission through free space. Visibility meter is the equipment to measure MOR.

In your question it is written that "In the case of rain and snow the transmission distance seems to be able to be estimated based on the rainfall and the snowfall." But the transmission distance of Infrared Communication can be estimated more correctly by using the visibility than the rainfall and the snowfall. Then the visibility more than the rainfall is the most important parameter for the estimation of the transmission distance in the rain.

ICSA has finished "A Study on Improving the Link Quality of the Free Space Optical transmission System" and verified the relation among the weather, the visibility and the optical transmission loss. Please refer to the result of the study.