A New Instrument for High-Speed, High Resolution Stereoscopic Photography of Falling Hydrometeors with Simultaneous Measurement of Fallspeed

We introduce a new instrument called the Multi-Angle Snowflake Camera (MASC). The MASC provides <30 \mu m resolution stereoscopic images of individual large falling hydrometeors. At the same time the MASC provides accurate measurements of hydrometeor fallspeed. Previously, manual photography of hydrometeors required initial collection on a flat surface, a process that is somewhat subject and remarkably finicky due to the fragile nature of the particles. Instruments such as the 2DVD are automated, leave the particle untouched and provide fallspeed data, but provide only 200 \mu m resolution silhouettes, which are insufficient to definitively assess the extent of riming on frozen hydrometeors. The MASC is like the 2DVD but uses a sensitive IR motion sensor for a trigger and actually photographs the particle surface from multiple angles. In the winters of 2012 and 2013, the MASC was deployed to Alta Ski Area near Salt Lake City for the NSF supported Wasatch Hydrometeor Aggregation and Riming Experiment (WASHARX) providing beautiful images and fallspeed data. The ability to obtain long-term continuous measurements of hydrometeor development and fallspeed suggests that MASC measurements may lead to improved parameterizations for aggregation, riming and precipitation in cold-storm weather models.