University of Oulu

Kaikkonen, V.A., Molkoselkä, E.O. & Mäkynen, A.J. A rotating holographic imager for stationary cloud droplet and ice crystal measurements. Opt Rev 27, 205–216 (2020).

A rotating holographic imager for stationary cloud droplet and ice crystal measurements

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Author: Kaikkonen, Ville A.1; Molkoselkä, Eero O.2; Mäkynen, Anssi J.2
Organizations: 1Unit of Measurement Technology, University of Oulu, Technology Park P.O. Box 127, 87400, Kajaani, Finland
2Optoelectronics and Measurement Techniques Unit, University of Oulu, P.O. Box 4500, 90014, Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.9 MB)
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Language: English
Published: Springer Nature, 2020
Publish Date: 2020-07-03


An optical cloud droplet and ice crystal measurement system ICEMET (icing condition evaluation method), designed for present icing condition monitoring in field conditions, is presented. The aim in this work has been to develop a simple but precise imaging technique to measure the two often missing parameters needed in icing rate calculations caused by icing clouds—the droplet size distribution (DSD) and the liquid water content (LWC) of the air. The measurement principle of the sensor is based on lens-less digital in-line holographic imaging. Cloud droplets and ice crystals are illuminated by a short laser light pulse and the resulting hologram is digitally sampled by a digital image sensor and the digital hologram is then numerically analyzed to calculate the present DSD and LWC values. The sensor has anti-icing heating power up to 500 W and it is freely rotating by the wind for an optimal sampling direction and aerodynamics. A volume of 0.5 cm³ is sampled in each hologram and the maximum sampling rate is 3 cm³/s. Laboratory tests and simulations were made to ensure the adequate operation of the measurement sensor. Computational flow dynamics simulations showed good agreement with droplet concentration distributions measured from an icing wind tunnel. The anti-icing heating of the sensor kept the sensor operational even in severe icing conditions; the most severe test conditions were the temperature − 15 °C, wind speed 20 m/s and the LWC 0.185 g/m³. The verification measurements made using NIST traceable monodisperse particle standard glass spheres showed that the ICEMET sensor measurement median diameter 25.54 µm matched well with 25.60 µm ± 0.70 µm diameter confidence level given by the manufacturer.

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Series: Optical review
ISSN: 1340-6000
ISSN-E: 1349-9432
ISSN-L: 1340-6000
Volume: 27
Issue: 2; SI
Pages: 205 - 216
DOI: 10.1007/s10043-020-00583-y
Type of Publication: A1 Journal article – refereed
Field of Science: 213 Electronic, automation and communications engineering, electronics
218 Environmental engineering
Funding: Open access funding provided by University of Oulu including Oulu University Hospital. This work was originally funded by Business Finland Tutl-grant ICEMET.
Copyright information: © The Author(s) 2020. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit