Campbell Scientific CS125 Present Weather Sensor - Manual (Page 14)

CS125 Present Weather Sensor
6
The descriptions in this section are not exhaustive. Please refer to
meteorological publications for further information on locating
weather instruments
The CS125 should be sited in a position representative of local weather conditions
and not of a specific microclimate (unless the analysis of microclimate weather is
being sought).
The CS125 has good resistance to background light but it is a good idea to avoid
locations where the transmitter is pointing at a light scattering or reflecting
surface. Ideally the receiver should point north in the northern hemisphere and
south in the southern hemisphere but this is not critical if the field of view does
not include a bright and scattering surface.
To give non-microclimatic measurements the CS125 should be sited away from
possible physical obstructions that could affect the fall of precipitation. The
CS125 should also be positioned away from sources of heat, electrical interference
and in such a position as to not have direct light on the sensor lenses. Whenever
possible, the CS125 should be located away from windbreaks.
Several zones have been identified upwind and downwind of a windbreak in
which the airflow is unrepresentative of the general speed and direction. Eddies
are generated in the lee of the windbreak and air is displaced upwind of it. The
height and depth of these affected zones varies with the height and to some extent
the density of the obstacle.
Generally, a structure disturbs the airflow in an upwind direction for a distance of
about twice the height of the structure, and in a downwind direction for a distance
of about six times the height. The airflow is also affected to a vertical distance of
about twice the height of the structure. Ideally, therefore, the CS125 should be
located outside this zone of influence in order to obtain representative values for
the region.
In order to reduce the service frequency with the unit, the CS125 should be placed
away from sources of contamination, in the case of roadside monitoring; larger
mounting poles can be used. More regular maintenance will be required when the
instrument is placed in areas where contamination is unavoidable or where
measurements may be safety critical.
The WMO recommend a sample volume height of 1.5 m. However, for
applications such as aviation or road visibility other heights may be appropriate.
NOTE
Receiver
Transmitter