This paper is devoted to the experimental quantitative characterization of
the shape and orientation distribution of ice particles in clouds. The
characterization is based on measured and modeled elevation dependencies of
the polarimetric parameters differential reflectivity and correlation
coefficient. The polarimetric data are obtained using a newly developed
35 GHz cloud radar MIRA-35 with hybrid polarimetric configuration and
scanning capabilities. The full procedure chain of the technical
implementation and the realization of the setup of the hybrid-mode cloud
radar for the shape determination are presented. This includes the
description of phase adjustments in the transmitting paths, the introduction
of the general data processing scheme, correction of the data for the
differences of amplifications and electrical path lengths in the transmitting
and receiving channels, the rotation of the polarization basis by
45°, the correction of antenna effects on polarimetric measurements,
the determination of spectral polarimetric variables, and the formulation of
a scheme to increase the signal-to-noise ratio. Modeling of the polarimetric
variables is based on existing back-scattering models assuming the spheroidal
representation of cloud scatterers. The parameters retrieved from the model
are polarizability ratio and degree of orientation, which can be assigned to
certain particle orientations and shapes. The developed algorithm is applied
to a measurement of the hybrid-mode cloud radar taken on 20 October 2014 in
Cabauw, the Netherlands, in the framework of the ACCEPT (Analysis of the
Composition of Clouds with Extended Polarization Techniques) campaign. The
case study shows the retrieved polarizability ratio and degree of orientation
of ice particles for a cloud system of three cloud layers at different
heights. Retrieved polarizability ratios are 0.43, 0.85, and 1.5 which
correspond to oblate, quasi-spherical, and columnar ice particles,
respectively. It is shown that the polarizability ratio is useful for the
detection of aggregation/riming processes. The orientation of oblate and
prolate particles is estimated to be close to horizontal while
quasi-spherical particles were found to be more randomly oriented
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