Determining the directional scattering coefficient from polar responses.

A method to measure the random incidence scattering coefficient has been described in ISO 17497-1. The method involves averaging the impulse responses for the sample in different orientations to isolate the specular component of the scattering. As such, the method does not distinguish between samples in which there is depth variation in only one direction, as in a cylinder, and textured surfaces with depth variation in many directions. Since computer model algorithms currently do not distinguish between these two types of surfaces, this may be an acceptable approximation. However, as computer models evolve to distinguish between these types of surfaces, directional scattering coefficients will be required. It is possible to calculate or measure the directional scattering coefficient from scattered polar responses, using either the correlation scattering coefficient described by Mommertz, in which the polar responses of a scattering sample and a flat surface are correlated, or the ratio of the energy in the specular zone and the total energy. Examples of calculated and measured directional scattering coefficients will be presented and discussed.