vdis

A disdrometer measures the drop size distribution and velocity of falling hydrometeors.

The 2-dimensional video-disdrometer (VDIS) comprises 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 through 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 responsible for handling the data-capture process, analysis of the data, and their 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 control both cameras with a synchronous line trigger signal.

To reconstruct observables like falling velocity, oblateness, etc. from the datastreams of the two cameras, the two optical paths are displaced vertically by about 6mm, typically. Measuring this distance and adjusting the background illumination are the two major calibration and maintenance tasks necessary for successful operation of the device.

Median volume diameter, assuming an ideal Marshall-Palmer type distribution
Number density
Rain amount

Cordoba, Argentina; Mobile Facility (CACTI)

• Latitude: -32.12641
• Longitude: -64.72837
• Publication Date: 2018-09-26
• Start Date: 2018-09-26
• End Date: 2019-04-29
• Last Updated: 2020-02-18

https://www.arm.gov/connect-with-arm/organization/instrument-mentors/list#vdis

Mary Jane Bartholomew

Brookhaven National Laboratory

Die Wang

Brookhaven National Laboratory

http://dx.doi.org/10.5439/1025315
Atmospheric Radiation Measurement (ARM) user facility. 2018, updated hourly. Video Disdrometer (VDIS). 2018-09-26 to 2019-04-29, ARM Mobile Facility (COR) Cordoba, Argentina; AMF1 (main site for CACTI) (M1). Compiled by D. Wang and M. Bartholomew. ARM Data Center. Data set accessed at http://dx.doi.org/10.5439/1025315.