A long time ago I did some reading on Mie scattering and atmospheric particulate counting and I got sidetracked on raindrop characterization.
I remember reading about light and laser based scatterometers that measured dark pulses as water droplets passed through the beam between a light source and a detector and attenuated it, and also bright pulses seen in detectors off to the side that recorded small and large angle scattered light from the water droplets.
Analysis of histograms of the amplitudes of the bright and dark pulses and to some extent other parameters allowed for an analysis of droplet size frequencies along the path that an aircraft flew in real time.
Question: What are those optical precipitation and water droplet characterization instruments called that they put on meteorological aircraft? How do they work?