Optical rain gauge
From AMS Glossary
optical rain gauge
A gauge that measures the scintillation in an optical beam produced by raindrops falling between a light source and an optical receiver.
By measuring the energy in selected frequency bands of the scintillation spectrum and comparing their ratios, the occurrence of precipitation, type of precipitation, and intensity of precipitation can be estimated.
Nystuen, J. A., et al. 1996. A comparison of automatic rain gauges. J. Atmos. Oceanic Technol.. 13. 62–73.