Imaging-based 3D Particle Tracking System for Field Characterization of Particle Dynamics in Atmospheric Flows

A particle tracking velocimetry apparatus is presented that is capable of measuring three-dimensional particle trajectories across large volumes, of the order of several meters, during natural snowfall events. Field experiments, aimed at understanding snow settling kinematics in atmospheric flows, were conducted during the 2021/2022 winter season using this apparatus, from which we show preliminary results. An overview of the methodology, wherein we use a UAV-based calibration method, is provided, and analysis is conducted of a select dataset to demonstrate the capabilities of the system for studying inertial particle dynamics in atmospheric flows. A modular camera array is used, designed specifically for handling the challenges of field deployment during snowfall. This imaging system is calibrated using synchronized imaging of a UAV-carried target to enable measurements centered 10 m above the ground within approximately a 4 m x 4 m x 6 m volume. Using the measured Lagrangian particle tracks we present data concerning 3D trajectory curvature and acceleration statistics, as well as clustering behavior using Voronoi analysis. The limitations, as well as potential future developments, of such a system are discussed in the context of applications with other inertial particles.