Abstract. The open source Video In Situ Snowfall Sensor (VISSS) is introduced as a novel instrument for the characterization of particle shape and size in snowfall. The VISSS consists of two cameras with LED backlights and telecentric lenses that allow accurate sizing and combine a large observation volume with relatively high resolution and a design that limits wind disturbance. VISSS data products include per-particle properties and integrated particle size distribution properties such as particle maximum extent, cross-sectional area, perimeter, complexity, and – in the future – sedimentation velocity. Initial analysis shows that the VISSS provides robust statistics based on up to 100,000 particles observed per minute. Comparison of the VISSS with collocated PIP and Parsivel instruments at Hyytiälä, Finland, shows excellent agreement with Parsivel, but reveals some differences for the PIP (Precipitation Imaging Package) that are likely related to PIP data processing and limitations of the PIP with respect to observing smaller particles. The open source nature of the VISSS hardware plans, data acquisition software, and data processing libraries invites the community to contribute to the development of the instrument, which has many potential applications in atmospheric science and beyond.;
