The disdrometer consists of three interdependent units: 1) a sensor unit, 2) an outdoor electronic unit, and 3) an indoor user terminal.

What is a disdrometer?

A disdrometer is an instrument that measures the size of rain drops. There are many different types of disdrometers. This disdrometer, which is developed by a small research company in Austria, is unique in that it records two, side view optical images of each raindrop. For this reason, it is called a 2D-Video-Disdrometer (or 2DVD for short).
 
 
 
 
 
 
 
 
 

Sensor Unit
Cameras

How does the 2DVD work?

Two planes of light transect the approximate 10 cm by 10 cm measurement area (just below the opening at the top of the disdrometer). As a rain drop falls into the sensor unit, it occludes each plane of light, thereby producing two "side image shadows" that are recorded by cameras (nested within the instrument, see above). The rain drop fallspeed is also measured. 

Everey three seconds, the rain drop data are "packaged" by the Outdoor Electronic Unit and transmitted via a radio frequency link to the Indoor User Terminal (located in the radar building).
 
 
 
 
 
 
 
 
 
 

• Measures a wide range of drop sizes
• Measures drop fallspeed
• Provides and estimate of drop shape
• Provides real time visualization of drop size, shape, and fallspeed

Outdoor Electronic Unit

How are 2DVD data used?

The intensity of the energy returned to a weather radar depends on the size of each rain drop. Furthermore, the number of rain drops at each size (for example, in a cubic meter of air) can vary significantly from cloud to cloud. This can make radar estimation of rainfall rate very difficult.

Disdrometer measurements allow us to better understand this drop size variability. In turn, this information is used to develop improved radar-based rainfall estimation techniques.
 
 
 
 

• The NSSL 2D-Video-Disdrometer (poster)