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| Titel |
Application of linear polarized light for the discrimination of frozen and liquid droplets in ice nucleation experiments |
| VerfasserIn |
T. Clauss, A. Kiselev, S. Hartmann, S. Augustin, S. Pfeifer, D. Niedermeier, H. Wex, F. Stratmann |
| 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. 4 ; Nr. 6, no. 4 (2013-04-19), S.1041-1052 |
| Datensatznummer |
250017877
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| Publikation (Nr.) |
 copernicus.org/amt-6-1041-2013.pdf |
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| Zusammenfassung |
| We report on the development and test results of the new optical particle
counter TOPS-Ice (Thermo-stabilized Optical Particle Spectrometer for the
detection of Ice). The instrument uses measurements of the cross-polarized
scattered light by single particles into the near-forward direction
(42.5° ± 12.7°) to distinguish between spherical and
non-spherical particles. This approach allows the differentiation between
liquid water droplets (spherical) and ice particles (non-spherical) having
similar volume-equivalent sizes and therefore can be used to determine the
fraction of frozen droplets in a typical immersion freezing experiment. We
show that the numerical simulation of the light scattered on non-spherical
particles (spheroids in random orientation) considering the actual
scattering geometry used in the instrument supports the validity of the
approach, even though the cross-polarized component of the light scattered by
spherical droplets does not vanish in this scattering angle. For the
separation of the ice particle mode from the liquid droplet mode, we use the
width of the pulse detected in the depolarization channel instead of the
pulse height. Exploiting the intrinsic relationship between pulse height and
pulse width for Gaussian pulses allows us to calculate the fraction of frozen
droplets even if the liquid droplet mode dominates the particle ensemble. We
present test results obtained with TOPS-Ice in the immersion freezing
experiments at the laminar diffusion chamber LACIS (Leipzig Aerosol Cloud
Interaction Simulator) and demonstrate the excellent agreement with the data
obtained in similar experiments with a different optical instrument. Finally,
the advantages of using the cross-polarized light measurements for the
differentiation of liquid and frozen droplets in the realistic immersion
freezing experiments are discussed. |
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