MASCDB, a database of images, descriptors and microphysical properties of individual snowflakes in free fall

Grazioli, Jacopo; Ghiggi, Gionata; Billault–Roux, Anne-Claire; Berne, Alexis

doi:10.1038/s41597-022-01269-7

Cited by 7 publications

References 71 publications

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

Bristow

Hartford

et al. 2023

Exp Fluids

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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.

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

Bristow

Hartford

et al. 2023

Exp Fluids

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MASCDB, a database of images, descriptors and microphysical properties of individual snowflakes in free fall

et al. 2022

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Snowfall information at the scale of individual particles is rare, difficult to gather, but fundamental for a better understanding of solid precipitation microphysics. In this article we present a dataset (with dedicated software) of in-situ measurements of snow particles in free fall. The dataset includes gray-scale (255 shades) images of snowflakes, co-located surface environmental measurements, a large number of geometrical and textural snowflake descriptors as well as the output of previously published retrieval algorithms. These include: hydrometeor classification, riming degree estimation, identification of melting particles, discrimination of wind-blown snow, as well as estimates of snow particle mass and volume. The measurements were collected in various locations of the Alps, Antarctica and Korea for a total of 2’555’091 snowflake images (or 851’697 image triplets). As the instrument used for data collection was a Multi-Angle Snowflake Camera (MASC), the dataset is named MASCDB. Given the large amount of snowflake images and associated descriptors, MASCDB can be exploited also by the computer vision community for the training and benchmarking of image processing systems.

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A universal scaling law for Lagrangian snowflake accelerations in atmospheric turbulence

Singh,

Pardyjak,

Garrett

2023

Physics of Fluids

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We use a novel experimental setup to obtain the vertical velocity and acceleration statistics of snowflakes settling in atmospheric surface-layer turbulence, for Taylor microscale Reynolds numbers (Reλ) between 400 and 67 000, Stokes numbers (St) between 0.12 and 3.50, and a broad range of snowflake habits. Despite the complexity of snowflake structures and the non-uniform nature of the turbulence, we find that mean snowflake acceleration distributions can be uniquely determined from the value of St. Ensemble-averaged snowflake root mean square (rms) accelerations scale nearly linearly with St. Normalized by the rms value, the acceleration distribution is nearly exponential, with a scaling factor for the (exponent) of −3/2 that is independent of Reλ and St; kurtosis scales with Reλ, albeit weakly compared to fluid tracers in turbulence; gravitational drift with sweeping is observed for St < 1. Surprisingly, the same exponential distribution describes a pseudo-acceleration calculated from fluctuations of snowflake terminal fall speed in still air. This equivalence suggests an underlying connection between how turbulence determines the trajectories of particles and the microphysics determining the evolution of their shapes and sizes.

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MASCDB, a database of images, descriptors and microphysical properties of individual snowflakes in free fall

Cited by 7 publications

References 71 publications

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

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

MASCDB, a database of images, descriptors and microphysical properties of individual snowflakes in free fall

A universal scaling law for Lagrangian snowflake accelerations in atmospheric turbulence

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