ABSTRACT
As has been seen from the discussion earlier in this book, the major difficulty in obtaining accurate temperatures in radiation thermometry is the requirement for knowledge of the emissivity of the target surface. While monochromatic radiation thermometry can achieve very high accuracy when the surface characteristics are well known, in many applications this is unfortunately not the case. The determination of spectral emissivities for the wide range of materials of industrial and scientific interest is by no means a simple matter, especially at high temperatures, where the value obtained will depend significantly upon the roughness of the surface and the degree to which chemical changes have taken place. There has, therefore, been a great deal of interest in the performance of radiation thermometers designed to be of general application, and to avoid the need for an accurate value of the emissivity.
