Disdrometer

Disdrometer are instruments for the determination of drop size and fall velocity distributions of precipitation particles. Drop spectra are required to e.g. determine the precipitation intensity from the radar reflectivity.

A traditional disdrometer works similar to a microphone. A small and, therefore, slow drop causes a small impulse on a measurement area. As larger and, therefore, faster a drop is, as higher is impulse. Every impulse is detected. The density of drops per volume can be determined by assuming a low of fall velocity.

The Parsivel (particle size and velocity) disdrometer (Fig. 1) works with a laser band instead of a measurement area. Hence, it is able to determine the drop size and velocity independently. To achieve that, a homogeneous laser band is sent from the sender head to the receiver head. If a hydrometeor (such as rain drops, hail, snowflakes) crosses the laser band, a part of the light is scattered outside the beam and the receiver head detects a decreased intensity of the light beam. For Hydrometeors with a diameter smaller than the band height (1 mm), the intensity reduction is linear to the cross-section area. For larger particles the intensity is linear to the size of the particle.

The velocity is determined from the duration of the shadowing by assuming the shape of the particle. For rain drops with a diameter of more than 1 mm, a flattening is considered. However, it is possible to identify different types of precipitation as rain, snow, graupel, hail, or drizzle.

In sum 28 Parsivel distrometer are operated in the KITcube. They can be operated independent of a power supply or network connection with a photovoltaics module and a mobile communication modem.