  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.
