Instrument : Video Disdrometer (VDIS)

Instrument Categories
Surface Meteorology

General Overview

A disdrometer is an instrument used to measure the drop size distribution and velocity of falling hydrometeors. The 2-dimensional video-disdrometer (vdis) is comprised of video cameras capable of observing individual hydrometeors from views perpendicular to each other. Two CCD line scan cameras are directed towards the measurement area. Objects passing thru the measurement area—which is determined by the cross-section of the two optical paths as seen from above—obstruct the light and are detected as shadows by the cameras. Each camera contains a small embedded computer which is responsible for handling the data capture process, the analysis of the data and its conversion and compression into a format suitable for further processing. Subsequently the data are transferred to the computer used for instrument control and final analysis. In order to identify individual precipitation particles by matching their views as seen by each of the cameras, it is necessary to synchronize the shutter and capture control of both cameras. To this end, both cameras use a synchronous line trigger signal. In order to reconstruct observables like falling velocity, oblateness, etc. from the data streams of the two cameras, the two optical paths are displaced vertically by a distance of typically about 6mm. Measuring this distance and adjusting the background illumination are the two major calibration and maintenance tasks necessary for successful operation of the device.

Output Datastreams

  • vdis : Video Disdrometer Drop Size Distribution
  • vdisdrops : Video Disdrometer Individual Drop Data

Primary Measurements

The following measurements are those considered scientifically relevant.


Southern Great Plains
SGPC1Browse DataCentral Facility, Lamont, OK
Tropical Western Pacific
TWPC1Browse DataCentral Facility, Manus I., PNG
TWPC3Browse DataCentral Facility, Darwin, Australia
ARM Mobile Facility
GANM1Browse DataGan Airport, Gan Island, Maldives
TMPM1Browse DataU. of Helsinki Research Station (SMEAR II), Hyytiala, Finland; AMF2


Mary Jane Bartholomew
(631) 344-2444