Objective determination of snow-grain characteristics from images

The determination of snow-grain characteristics (such as type or size) is crucial for validating snow models and interpreting remote-sensing data. Until now, the size and type of snow grains have been estimated in the field. Nowadays, the transport of a snow sample in iso-octane allows laboratory analyses. The objective analysis of snow-grain digital images has been developed at the Centre d'Etudes de la Neige since the mid 1980s. The images are taken in a cold room and stored on a video disk. The calculation of the relevant parameters for snow characterization has been developed. Recently, the hardware- and software-systems have been upgraded, allowing quicker and easier analyses. Finally a procedure designed to determine snow types from image analysis has been developed and calibrated using 65 snow samples. For that purpose, independent experts have determined the snow type (as defined by the International Classification) of each sample. The procedure has been verified using an independent set of snow images. This semi-automated determination gives 97% correct results on granular-snow types. However, it is not reliable for precipitation particles.