Thies CLIMA 5.4110 00 Series, Инструкция по эксплуатации

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3 Mode of Operation of the Laser Precipition Monitor
A laser-optical beaming source (laser diode and optics) produces a parallel light-beam (infrared,
785 nm, not visible). A photo diode with a lens is situated on the receiver side in order to measure
the optical intensity by transforming it into an electrical signal.
228 mm
0.75
mm
20mm
Particle
Infrared light beam
Figure 1: Measurement of the precipitation particle
When a precipitation particle falls through the light beam (measuring area 45,6cm²(7inch²)) Figure
1: Measurement of the precipitation particle ) the receiving signal is reduced. The diameter of the
particle is calculated from the amplitude of the reduction. Moreover, the fall speed of the particle is
determined from the duration of the reduced signal.
Figure 2: Explanation of the measuring principle
The measured values are processed by a signal processor (DSP), and checked for plausibility (e.g.
edge hits). Calculation comprises the intensity, quantity, and type of precipitation (drizzle, rain,
snow, soft hail, hail as well as mixed precipitation), and the particle spectrum (distribution of the
particles over the class binning).
The type of precipitation is determined from the statistic proportion of all particles referring to
diameter, and velocity. These proportions have been tested scientifically (e.g. Gunn, R., and
Kinzer, G.D., 1949, "The terminal velocity of fall for water droplets in stagnant air,"
J. of
Meteorology , Vol. 6, pp. 243–248). In addition, temperature is included in order to improve the
identification: Precipitations with a temperature of above 9 °C are automatically accepted as liquid
(exception: soft hail, and hail), and with a temperature of below –4°C as solid. In the temperature
range between, all forms of precipitation might occur.
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