Use of circular cylinders as surrogates for hexagonal pristine ice crystals in scattering calculations at infrared wavelengths

Yong-Keun Lee, Ping Yang, Michael I. Mishchenko, Bryan A. Baum, Yong X. Hu, Hung-Lung Huang, Warren J. Wiscombe, Anthony J. Baran
2003 Applied Optics  
We investigate the errors associated with the use of circular cylinders as surrogates for hexagonal columns in computing the optical properties of pristine ice crystals at infrared ͑8 -12-m͒ wavelengths. The equivalent circular cylinders are specified in terms of volume ͑V͒, projected area ͑ A͒, and volumeto-area ratio that are equal to those of the hexagonal columns. We use the T-matrix method to compute the optical properties of the equivalent circular cylinders. We apply the
more » ... time-domain method to compute the optical properties of hexagonal ice columns smaller than 40 m. For hexagonal columns larger than 40 m we employ an improved geometric optics method and a stretched scattering potential technique developed in previous studies to calculate the phase function and the extinction ͑or absorption͒ efficiency, respectively. The differences between the results for circular cylinders and hexagonal columns are of the order of a few percent. Thus it is quite reasonable to use a circular cylinder geometry as a surrogate for pristine hexagonal ice columns for scattering calculations at infrared ͑8 -12-m͒ wavelengths. Although the pristine ice crystals can be approximated as circular cylinders in scattering calculations at infrared wavelengths, it is shown that optical properties of individual aggregates cannot be well approximated by those of individual finite columns or cylinders.
doi:10.1364/ao.42.002653 pmid:12777000 fatcat:jf2ytlrvknhmdbmumhk54aroh4