Measurements of drop size distributions at McGill

The measurements and interpretation of raindrop size distributions (DSD) concentrates on the shapes of the DSD functions for equilibrium and non-equilibrium cases, as well as identifying the shapes for different hydrometeors (such as rain, freezing rain, and melting snow). The research is conducted from an observational point of view, taking the advantage of the McGill's remote sensing capabilities, and the following three sensors:

(1) The Joss-Waldvogel Distrometer, JWD: A Swiss instrument that converts raindrops' vertical momentum into drop diameters. It is the classic instrument for the measurement of DSD's.

(2) The Optical Spectro Pluviometre, OSP: It was borrowed from the Centre de Recherches en Physique de l'Environnement Terrestre et Planétaire (CETP), in France, and its principle is the optical occultation of a parallel beam of light by the raindrops during their fall.

(3) The Precipitation Occurrence Sensor System, POSS: This is a bistatic, X-band, Doppler radar, designed by Atmospheric Environment Service (AES) of Canada. The POSS measures a signal whose frequency is proportional to the raindrop Doppler velocity, and whose amplitude is proportional to the raindrop diameter.

The volume of sampling for the three instruments is very different. However, their observations are all consistent to each other.