Your answer tells that the measurement with visibility meter is the best.
The visibility meter can measure only the condition of the short range
around the meter and many equipments are needed for the measurement of
the condition of the long range of 5km according to the information of
the weather bureau and the manufacturer of the meter. I think that many
kinds of measurements were finished until now and I wonder that there is
a large difference between the visibility meter and the naked eye. Please
let me know your opinion.
Weather bureau measures the visibility with the naked eye until now. The
meter is deployed partially, but many cases adopt the measurement with
the naked eye now. It is considered that the difference between them is
small especially in the case of the bad condition of the Free Space Infrared
As you mention, the measurement of the transparency of the transmission
path is needed in order to know the correct visibility. The purpose of
our experiment is not to get the equivalent data to the weather bureau,
but to verify the availability of the data from the weather bureau near
by the setup place as the necessary visibility data for the link design
at the time of actual deployment of Infrared Communication.
The actual purpose of this experiment is to verify the relation between our data measured by the visibility meter and the data of the Meteorological Agency at Takebashi in Tokyo. The relation coefficient was closely verified to be about 0.9`1.1 between both data. That is the experimental data of one area and is not verified in every area. It is necessary to get the data in various areas in future.
Visibility meter was used in this experiment because the automatic measurement
is possible and it is an experiment method in order to cope with the influence
of weather and the cause of obstruction. From the result of this experiment
we think that the link design is possible using the data from the weather
bureau even if there is not the actual data of the visibility of the setup