Vaisala FD12P - Manual (Page 109)

Chapter 5 _______________________________________________________ Functional Description
VAISALA _______________________________________________________________________ 109
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Figure 30 Precipitation Type Determination Principle
The precipitation types can be divided into four main categories:
- Liquid precipitation
- Frozen precipitation
- Mixed precipitation
- Unknown precipitation
The types and their detection criteria are listed below.
Liquid Precipitation
In liquid precipitation, the optical and the DRD12 intensities are near
each other, or the DRD12 intensity is higher. Rain and drizzle are
separated by the highest peak signal (largest droplet). If liquid
precipitation is detected below 0 °C (TS), it is indicated as freezing
rain or freezing drizzle (ZR, ZL).
NOTE The FD12P freezing precipitation detection is based on the practical
definition of "rain (or drizzle) freezing on surfaces", not on detecting
supercooled water.
a. Rain: If the maximum droplet size is bigger than the
Drizzle limit, the precipitation type is rain. The Light rain
limit and Heavy rain limit are (approximately) the two-