Collision frequencies of raindrops

Using an exponential model spectrum for raindrop sizes, calculations are made of how often raindrops collide with one another. The collision of a large drop with another occurs after an interval of a few seconds. Large drops are likely to be markedly aspherical, and to oscillate, rather than to follow collectively a mean canting angle. Such variabilities should be considered in calculating depolarization and differential attenuation of microwaves in rain.