Measuring and quantifying scatter from a variety of sample types

Abstract

When using the BRDF to learn about surface statistics or to estimate hemispherical scatter from in-plane measurements the assumption is usually made that the surface is isotropic. Unfortunately, this is often not the case; for example a diamond turned mirror is not isotropic. Other common examples are rolled surfaces and situations where scatter is mostly caused by small discrete surface features such as scratches, pits or particles. Another example is scatter from an extended edge that is much longer than the illuminated spot. In these situations the measurements may be made differently and quantified in different units (such as area/sr or 1/deg instead of the common 1/sr associated with BRDF) in order to have a result that can reliably characterize the scatter source. The situation is further complicated by the fact that the popular stray radiation codes accept scatter data only in the standardized BRDF format with units of 1/sr. This paper reviews these situations for both measurement and analysis issues.