Simultaneous measurement of falling velocity and size of large droplets using a laser system

A laser system that simultaneously measures the falling velocity and size of large particles is constructed. In this system, a specially designed laser Doppler velocimeter (LDV) measures selectively the vertically falling velocity vector, and the size is measured using two beams intersecting at right angles in the center of the sampling volume of the LDV. The two values measured by the two beams are considered as the sizes projected to the illuminating directions of the beams. This system is applied to the measurement of rain droplets and snowflakes, and it gives clear relations between the falling velocity and the size.