Imaging-based 3D particle tracking system for field characterization of particle dynamics in atmospheric flows

Abstract

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 3D PTV System for Atmospheric Flows 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×4 m×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 Voronoï analysis. The limitations, as well as potential future developments, of such a system are discussed in the context of applications with other inertial particles.

Calibration method for binocular vision system with large field of view based on small target image splicing

“…where t donates the total number of control points on a small target. p r_ijk is the real pixel coordinate of the kth point on the ith target in the jth spliced images for the right camera, and ⌢ p r_ijk (K r , k r , R rj , T rj , W rij ) is the calculated coordinate by equations ( 14) and (16). p l_ijk and ⌢ p l_ijk (K l , k l , R rj , T rj , R, T, W lij ) are the coordinates corresponding to the left camera.…”

“…The virtual 3D targets built by numerous single points are also used for calibration. But the location information of points needs to be provided by additional equipment such as unmanned aerial vehicles [15,16] and laser trackers [17], increasing the cost and complexity of calibration. Compared with using 1D and 3D targets, the calibration methods using 2D targets are widely used and have better balanced performance in terms of efficiency, flexibility, and cost.…”

Lagrangian particle tracking in the atmospheric surface layer

“…We use the more general descriptor LPT because we do not only report velocity statistics. Recently, 3D LPT field experiments with natural snowfall have been conducted to study snow-settling dynamics [14]. Artificial snow has also been used to study the wake of a vertical axis wind turbine [15].…”