Inter-comparison of Rainfall Measurements from 1- and 2-Dimensional Video Disdrometers

Student: Trey Anderson

Major: Physics and Astronomy

Mentors: Dr. Michael L. Larsen

Department: Physics and Astronomy

Inter-comparison of Rainfall Measurements from 1- and 2-Dimensional Video Disdrometers

A disdrometer (from DIStribution of DROps METER) is a device capable of measuring properties (like fall speed, size, and shape) of individual rain drops or snow flakes. Multiple disdrometers are available on the market and use a variety of different measurement techniques. Two of these are manufactured by Joanneum Research the 2-Dimensional Video Disdrometer (2DVD) and the 1-Dimensional Video Disdrometer (1DVD); these devices use high-speed cameras taking more than 50000 images per second to obtain information about each drop falling through the instrument.

The 2DVD has been on the market since the early 1990s and has been used in hundreds of scientific studies related to verifying radar and satellite-based estimations of rain accumulations and rain rates. The instrument is well-known to be generally accurate, but has some limitations in reliability of detecting small (less than 0.5 mm) drops, measuring rainfall in windy conditions, and identifying the exact size of individual drops.

The 1DVD is a new instrument that uses many of the same measurement techniques as the 2DVD, but with several key differences; it is far less expensive (less than half the cost) and may be able to record drop sizes more precisely due to its included camera having approximately three times the resolution of the 2DVD cameras. However, the 1DVD only has a single camera which prohibits exact measurement of drop fall position and requires processing methods that either assume a particular shape or fall speed for each drop.

In this study we present comparisons of data collected by two 2-Dimensional Video Disdrometers (SN074 and SN098) and two 1-Dimensional Video Disdrometers (SN03 and SN04) located within close proximity at The College of Charleston at Stono Preserve. The data collected from several rain events includes comparisons of rain accumulations and drop size distributions between instruments. It is found that there are distinct differences in measurements between the instruments that vary depending upon the size of the raindrop being measured.