Determination of Emissivity by Using Reflected Thermal Radiation

The determination of emissivity is crucial in any temperature measurement using radiation thermometry. Without this knowledge, large measurement uncertainties result. There is a lack of information on emissivity for common materials. Where there are databases, these databases often give emissivity for a specific material in a range or give emissivity for different conditionings of the material. This information may not apply to certain uses of the material. This creates quite a bit of doubt for anyone making measurements in the field. What is needed is a method to determine emissivity for a material object in the field. In 2011, Yamada and Ishii discussed a method that was set up in a fixed geometry to determine the emissivity of a specular object. In this paper, a method is discussed to determine the emissivity of both specular and diffuse objects using a thermal radiation source. The theory is presented. Then, practical measurements which were made are discussed. These measurements are compared to emissivity determined by other methods.