Field-scale volumetric particle tracking system for snow settling measurement

Snow settling dynamics are a crucial parameter in our predictive capability of important processes such as cloud lifetime and ground snow accumulation. Recent studies have investigated the particle-turbulence interactions that modulate these dynamics for the first time in the field (Nemes et al. JFM, 2017; Li et al., JFM, 2021), utilizing large-scale particle tracking velocimetry (PTV), but have thusfar been limited to 2D measurements. Volumetric PTV can provide richer information of snow settling dynamics for longer time scales than in 2D, as particles do not leave the measurement region as frequently due to turbulent motions. Herein we present a field-scale volumetric PTV system using four cameras that is designed to be low-cost and enable flexible deployment for various arrangements to capture motion in different 3D volumes, depending on the resolution desired and snowfall density. A drone-based method for calibrating such a system was developed that can be readily extended to measurements over sample volumes at different scales, including regions of interest far above the ground. The performance of the system is evaluated using artificial snow particles over a sample volume of 3x3x3 m³ prior to field deployments with natural snow.