Mesa Photonics’ Cloud Droplet Measurement System (CDMS) implements a compact optical imaging technology for in situ measurement of cloud droplet size distribution function and droplet number density in the size range of 10–1000 µm. The method is based on analysis of scattered light images of individual droplets from an image frame containing images of multiple droplets illuminated by a sheet-shaped light source. The instrument is equipped with a wireless telecommunication system that broadcasts the data to the ground station. The data can also be stored on a local hard drive. The preferred deployment platform is tethered balloon system (TBS).