User`s guide

Chapter 2 __________________________________________________________ Product Overview
VAISALA_______________________________________________________________________ 71
accurate evaluation of the weather type according to the WMO and
NWS code tables.
PWD12 is an intelligent, multi-variable sensor for automatic weather
observing systems. The sensor combines the functions of a forward
scatter visibility meter and a present weather sensor. PWD12 can
measure the intensity and amount of both liquid and solid precipitation.
If the detector is equipped with an optional background luminance
sensor, it can also measure ambient light.
PWD22 is equipped with two Vaisala RAINCAP® sensor elements to
improve detection sensitivity during light precipitation events – even
light drizzle is detected. With a visibility measurement range of 10–
20,000 meters, the Vaisala Present Weather Detector PWD22 is a two-
in-one forward scatter visibility and present weather sensor. PWD22 is
recommended for automatic weather stations (especially low-power
AWSs) that are used for general meteorological and aviation
applications. The PWD22’s ability to detect freezing precipitation
makes it possible to issue warnings when the weather presents safety
hazards.
Ceilometer
0105-031
Figure 66 Ceilometer CT25K
The CT25K laser ceilometer is a new generation general purpose cloud
height sensor. CT25 employs pulsed diode laser LIDAR (Light
Detection and Ranging) technology for detection of clouds,
precipitation and other obstructions to vision, and accurate
determination of cloud heights and vertical visibility.