Two different philosophies are pursued in the parameterization of particle scattering. One approach is to carry-out the scattering calculations off-line and provide either look-up tables or simple functional fits to these calculations. These are usually based on Mie theory although other scattering results may be used. The approach of Fu and Liou [1993] for ice particles is based on geometric optics whereas that of Hu and Stamnes [1993] employs Mie theory to generate tables of scattering functions relevant to water clouds. This method is also universally used in parameterizing the optical properties of both stratospheric and tropospheric aerosol [e.g. Lacis and Mishchenko, 1994]. The other approach is to use a simple scattering theory as a basis for the parameterization and then adapt it to provide the relevant optical properties of particles. This approach tends to be used for larger particles such as cloud particles and has been applied to parameterize the optical properties of both spherical ice and water particles . An example of this approach is that of Chylek and Klett [1991] for hexagonal ice particles although other examples exist in literature published prior to 1991.