The destructive potential of gravitational mass flows, such as snow avalanches, has a large socio-economic impact in mountainous regions. Our current understanding of flow dynamics on a particle level is mostly based on laboratory experiments and computer simulations. Measurement techniques of snow avalanches usually involve either non-invasive externally observable characteristics or invasive flow-obstacle interactions. An appropriate non-invasive in-flow measurement method, that allows to assess the influence of snow and particle properties, such as temperature, density, size, or shape, on processes like segregation, phase separation, and eventually flow mobility, is missing.