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Microphysical properties and fall speed measurements of snow ice crystals using the Dual Ice Crystal Imager (D-ICI)
Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.ORCID iD: 0000-0003-3701-7925
Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
2020 (English)In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 13, p. 1273-1285Article in journal (Refereed) Published
Abstract [en]

Accurate predictions of snowfall require good knowledge of the microphysical properties of the snow ice crystals and particles. Shape is an important parameter as it strongly influences the scattering properties of the ice particles, and thus their response to remote sensing techniques such as radar measurements. The fall speed of ice particles is another important parameter for both numerical forecast models as well as representation of ice clouds and snow in climate models, as it is responsible for the rate of removal of ice from these models.

We describe a new ground-based in situ instrument, the Dual Ice Crystal Imager (D-ICI), to determine snow ice crystal properties and fall speed simultaneously. The instrument takes two high-resolution pictures of the same falling ice particle from two different viewing directions. Both cameras use a microscope-like setup resulting in an image pixel resolution of approximately 4 µm pixel−1. One viewing direction is horizontal and is used to determine fall speed by means of a double exposure. For this purpose, two bright flashes of a light-emitting diode behind the camera illuminate the falling ice particle and create this double exposure, and the vertical displacement of the particle provides its fall speed. The other viewing direction is close-to-vertical and is used to provide size and shape information from single-exposure images. This viewing geometry is chosen instead of a horizontal one because shape and size of ice particles as viewed in the vertical direction are more relevant than these properties viewed horizontally, as the vertical fall speed is more strongly influenced by the vertically viewed properties. In addition, a comparison with remote sensing instruments that mostly have a vertical or close-to-vertical viewing geometry is favoured when the particle properties are measured in the same direction.

The instrument has been tested in Kiruna, northern Sweden (67.8∘ N, 20.4∘ E). Measurements are demonstrated with images from different snow events, and the determined snow ice crystal properties are presented.

Place, publisher, year, edition, pages
Copernicus Publications , 2020. Vol. 13, p. 1273-1285
National Category
Aerospace Engineering
Research subject
Atmospheric science
Identifiers
URN: urn:nbn:se:ltu:diva-78097DOI: 10.5194/amt-13-1273-2020ISI: 000521147100001Scopus ID: 2-s2.0-85082337081OAI: oai:DiVA.org:ltu-78097DiVA, id: diva2:1415385
Note

Validerad;2020;Nivå 2;2020-03-18 (johcin)

Available from: 2020-03-18 Created: 2020-03-18 Last updated: 2020-04-09Bibliographically approved

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Kuhn, ThomasVázquez-Martín, Sandra

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Space Technology
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Atmospheric Measurement Techniques
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Kuhn, T. (2020). Dual Ice Crystal Imager (D-ICI): images of snow particles, Kiruna, 2014. Svensk Nationell Datatjänst

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