ABSTRACT
For all radiation transfer calculations, we need to have spectral or total radiative properties of surfaces and the media in which radiative energy propagates. These properties are to be obtained from experiments, and often constitute the bottleneck in predictions as they usually are not available. It is possible to derive these properties for homogeneous, optically smooth media using the electromagnetic wave theory. As we will discuss in Chapter 14, the electromagnetic (EM) theory yields useful trends and provides a unifying basis to help explain radiation phenomena. However, the analyses are inadequate to predict the properties of surfaces that are not perfectly clean or have varying amounts of contaminants or oxides on them. In most practical applications, surfaces have surface roughness that is difcult to completely specify. Variations of measured radiative properties as a function of these and other parameters are discussed in this chapter, where we emphasize the properties of real materials. In addition to typical properties, some other examples are given to demonstrate that a careful examination of individual properties must be made to properly select property values for radiative exchange calculations.
