Digital crossed-beam holography for<i>in situ</i>imaging of atmospheric ice particles

Raupach, S. M. F.; Vössing, H.; Curtius, Joachim; Borrmann, Stephan

doi:10.1088/1464-4258/8/9/014

Cited by 34 publications

(33 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Digital in-line holography has been previously used in a series of airborne (Conway et al, 1982;Beals et al, 2015) and ground-based field instruments (Thompson, 1964;Kozikowska et al, 1984;Borrmann and Jaenicke, 1993;Raupach et al, 2006;Henneberger et al, 2013). In comparison to other in situ cloud probes, holographic imagers have specific advantages and disadvantages (see Baumgardner et al, 2011).…”

mentioning

confidence: 99%

HoloGondel: in situ cloud observations on a cable car in the Swiss Alps using a holographic imager

et al. 2017

View full text Add to dashboard Cite

Abstract. In situ observations of cloud properties in complex alpine terrain where research aircraft cannot sample are commonly conducted at mountain-top research stations and limited to single-point measurements. The HoloGondel platform overcomes this limitation by using a cable car to obtain vertical profiles of the microphysical and meteorological cloud parameters. The main component of the HoloGondel platform is the HOLographic Imager for Microscopic Objects (HOLIMO 3G), which uses digital in-line holography to image cloud particles. Based on two-dimensional images the microphysical cloud parameters for the size range from small cloud particles to large precipitation particles are obtained for the liquid and ice phase. The low traveling velocity of a cable car on the order of 10 m s −1 allows measurements with high spatial resolution; however, at the same time it leads to an unstable air speed towards the HoloGondel platform. Holographic cloud imagers, which have a sample volume that is independent of the air speed, are therefore well suited for measurements on a cable car. Example measurements of the vertical profiles observed in a liquid cloud and a mixed-phase cloud at the Eggishorn in the Swiss Alps in the winters 2015 and 2016 are presented. The HoloGondel platform reliably observes cloud droplets larger than 6.5 µm, partitions between cloud droplets and ice crystals for a size larger than 25 µm and obtains a statistically significantly size distribution for every 5 m in vertical ascent.

show abstract

mentioning

confidence: 99%

HoloGondel: in situ cloud observations on a cable car in the Swiss Alps using a holographic imager

et al. 2017

View full text Add to dashboard Cite

show abstract

“…The digital holographic method has already been used in atmospheric science in some instruments, starting with a prototype instrument (Lawson and Cormack, 1995), airborne measurements (HOLODEC, Fugal et al, 2004;HOLODEC2, Spuler and Fugal, 2011), ground-based measurements (Raupach et al, 2006), and also lab measurements with HOLIMO I (HOLographic Imager for Microscopic Objects I, Amsler et al, 2009), the predecessor of HOLIMO II. Many of these instrument projects showed promising results, but have not been continued, likely because of the time and effort needed for the complex data analysis.…”

Section: Published By Copernicus Publications On Behalf Of the Europementioning

confidence: 99%

“…In contrast to other holographic instruments Raupach et al, 2006), which are designed with an open path configuration, HOLIMO II samples air through a circular inlet with a diameter of 50 mm. Although this leads to anisokinetic sampling effects (see Sect.…”

Section: Description Of the Instrumentmentioning

confidence: 99%

HOLIMO II: a digital holographic instrument for ground-based in situ observations of microphysical properties of mixed-phase clouds

et al. 2013

View full text Add to dashboard Cite

Abstract. Measurements of the microphysical properties of mixed-phase clouds with high spatial resolution are important to understand the processes inside these clouds. This work describes the design and characterization of the newly developed ground-based field instrument HOLIMO II (HOLographic Imager for Microscopic Objects II). HOLIMO II uses digital in-line holography to in situ image cloud particles in a well-defined sample volume. By an automated algorithm, two-dimensional images of single cloud particles between 6 and 250 µm in diameter are obtained and the size spectrum, the concentration and water content of clouds are calculated. By testing the sizing algorithm with monosized beads a systematic overestimation near the resolution limit was found, which has been used to correct the measurements.Field measurements from the high altitude research station Jungfraujoch, Switzerland, are presented. The measured number size distributions are in good agreement with parallel measurements by a fog monitor (FM-100, DMT, Boulder USA). The field data shows that HOLIMO II is capable of measuring the number size distribution with a high spatial resolution and determines ice crystal shape, thus providing a method of quantifying variations in microphysical properties. A case study over a period of 8 h has been analyzed, exploring the transition from a liquid to a mixed-phase cloud, which is the longest observation of a cloud with a holographic device. During the measurement period, the cloud does not completely glaciate, contradicting earlier assumptions of the dominance of the Wegener-Bergeron-Findeisen (WBF) process.

show abstract

“…Holographic methods have also been used to study ice particles (Raupach et al 2006). Evaluations of a prototype for aircraft in situ measurements show that details as small as 6.5 mm can be resolved in this way (Amsler et al 2009;Spuler and Fugal 2011).…”

Section: Introductionmentioning

confidence: 99%

Improved Imaging and Image Analysis System for Application to Measurement of Small Ice Crystals

Kühn

Grishin

Sloan

2012

Journal of Atmospheric and Oceanic Technology

View full text Add to dashboard Cite

Accurate knowledge of ice particle size and shape distribution is required for understanding of atmospheric microphysical processes. While larger ice particles are easily measured with a variety of sensors, the measurement of small ice particles with sizes down to a few micrometers remains challenging. Here the authors report the development of a system that measures the size and shape of small ice particles using a novel combination of high-resolution imaging and high-speed automated image classification. The optical system has a pixel resolution of 0.2 mm and a resolving power of approximately 1 mm. This imaging instrument is integrated into a cryogenic flow tube that allows precise control of experimental conditions. This study also describes an automated method for the high-speed analysis of high-resolution particle images. Each particle is located in the image using a Sobel edge detector, the border is vectorized, and a polygon representing the border is found. The vertices of this polygon are expressed in complex coordinates, and an analytic implementation of Fourier shape descriptors is used for piecewise integration along the edges of the polygon.The authors demonstrate the capabilities of this system in a study of the early-stage growth of ice particles, which are grown for approximately 1 min at fixed temperature and saturated water vapor concentrations in the cryogenic flowtube. Ice particle shapes and size distributions are reported and compared with habit diagrams found in the literature. The capability of the shape recognition system is verified by comparison with manual classification.

show abstract

Digital crossed-beam holography forin situimaging of atmospheric ice particles

Cited by 34 publications

References 26 publications

HoloGondel: in situ cloud observations on a cable car in the Swiss Alps using a holographic imager

HoloGondel: in situ cloud observations on a cable car in the Swiss Alps using a holographic imager

HOLIMO II: a digital holographic instrument for ground-based in situ observations of microphysical properties of mixed-phase clouds

Improved Imaging and Image Analysis System for Application to Measurement of Small Ice Crystals

Contact Info

Product

Resources

About