Campbell CS120A, Instruction Manual

Page: 16 / 94

CS120A and CS125 Visibility and Present Weather Sensors
4
Figure 1-2. Signals from large, slow falling snowflakes and smaller, faster,
raindrops
The CS125 also has a temperature sensor. These 3 parameters, fall speed, size and
temperature are used to identify the type of particle. If an additional external
temperature and relative humidity probe is connected then a wet-bulb temperature
can be calculated. This provides useful additional information identifying particles
more accurately especially, between liquid and frozen around 0°C.
Figure 1-3 shows how these temperatures are used to define possible precipitation
types around 0°C.
Figure 1-3. Defining possible precipitation types based on wet bulb and
dry bulb temperatures
The processing algorithm then works with several ‘maps’ such as Figure 1-4 to
identify each particle.