Campbell Scientific PWS100 Present Weather Sensor - Manual (Page 17)

Section 4. Overview
The PWS100 Present Weather Sensor is a laser based sensor capable of
determining precipitation and visibility parameters for automatic weather
stations including road, marine and airport stations. Due to its advanced
measurement technique and fuzzy logic algorithms, the PWS100 can determine
each individual precipitation particle type from accurate size and velocity
measurements and the structure of the received signal.
The system can output visibility and precipitation related weather codes such
as those detailed in the World Meteorological Organisation (WMO) SYNOP
code, those used as part of a METAR weather report and those previously used
by the US National Weather Service (NWS).
Further details of precipitation can be given in terms of drop size distributions
(DSD) and particle size / velocity maps to give better indications of
precipitation intensity. Such distributions can then be used in soil erosion
studies.
The PWS100 comprises a Digital Signal Processor (DSP) housing unit
connected to a sensor arm, comprising one laser head and two sensor heads.
Each of the sensor heads is 20
° off axis to the laser unit axis, one in the
horizontal plane, the other in the vertical plane. The DSP housing is fixed via a
mounting bracket to a mast, though a tripod can be used for temporary sites.
Figure 4-1 shows the PWS100 mounted on a pole.
An optional CS215-PWS temperature and humidity sensor is normally
supplied and plugs directly into the PWS100. That sensor is used to improve
the accuracy of weather coding by the PWS, in particular in respect of
discriminating between snow and rain and also fog/mist and dust.
FIGURE 4-1. PWS100
4-1