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| Titel |
HOLIMO II: a digital holographic instrument for ground-based in situ observations of microphysical properties of mixed-phase clouds |
| VerfasserIn |
J. Henneberger, J. P. Fugal, O. Stetzer, U. Lohmann |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 6, no. 11 ; Nr. 6, no. 11 (2013-11-06), S.2975-2987 |
| Datensatznummer |
250085102
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| Publikation (Nr.) |
 copernicus.org/amt-6-2975-2013.pdf |
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| Zusammenfassung |
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. |
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