Four-color pyrometry for metal emissivity characterization

Remote measurement of temperature requires thorough knowledge of the surface emissivity characteristics. Emissivity can be thought of as a figure of merit to how closely a material follows a blackbody radiator. The emissivity behavior often has a wavelength dependence and with accurate emissivity prediction, the temperature of a surface can be determined using a passive IR camera. It is both important to create precise emissivity models as well as develop instrumentation that can acquire the data accurately. To develop a model for materials such as metals, it can be observed that the primary contribution to the absorption characteristics can be attributed to the free electron plasma. It can be shown that the emissivity for heated metals in thermal equilibrium can be modeled as a second order polynomial. Consequently, a four color optical pyrometer can be used to accurately determine emissivity profile so that the true temperature can be determined.