## Abstract

We calculated the scattering and absorption properties of randomly
oriented hexagonal ice columns using *T*-matrix theory,
employing analytic orientation averaging, and the finite-difference
time-domain method, which uses a numerical procedure to simulate random
orientation. The total optical properties calculated are the
extinction efficiency, absorption efficiency, single-scattering albedo,
and the asymmetry parameter. The optical properties are calculated
at the wavelengths of 0.66, 8.5, and 12 µm, up to a size
parameter of 20 at 0.66 µm and 15 at the two other
wavelengths. The phase-matrix elements *P*11, *P*12, and
*P*22 are also calculated and compared, up to a size parameter
of 20 at 0.66 µm and 15 at 12.0 µm. The
scattering and absorption solutions obtained from the two independent
electromagnetic methods are compared and contrasted, as well as the
central processing unit time and memory load for each size
parameter. It is found that the total optical properties calculated
by the two methods are well within 3% of each other for all three
wavelengths and size parameters. In terms of the phase-matrix
elements it is found that there are some differences between the
*T*-matrix and the finite-difference time-domain methods
appearing in all three elements. Differences between the two
methods for the *P*11 element are seen particularly at
scattering angles from approximately 120° to 180°; and at the
scattering angle of 180°, relative differences are less than
16%. At scattering angles less than 100°, agreement is generally
within a few percent. Similar results are also found for the
*P*12 and *P*22 elements of the phase matrix. The
validity of approximating randomly oriented hexagonal ice columns by
randomly oriented equal surface area circular cylinders is also
investigated in terms of the linear depolarization ratio.

© 2001 Optical Society of America

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