On the effects of temperature dependence of spectral emissivity in industrial radiation thermometry

Most industrial applications of radiation thermometry require corrections of the measured signal to account for both the emissivity of the target and reflected radiation from the target's surroundings. The accuracy of these corrections relies on detailed knowledge of the target emissivity, Even so, the temperature dependence of the emissivity in some cases creates an ambiguity in the components of the target radiance that is fundamentally unresolvable. This ambiguity leads to an enhancement of the measurement uncertainty, sometimes catastrophically. In other cases the temperature dependence of the emissivity enhances the sensitivity of the measured temperature to changes in target temperature, resulting in a reduced measurement uncertainty. As well as an intrinsic temperature dependence of emissivity, there is also an induced temperature dependence due to the spectral dependence of the emissivity when broadband temperature measurements are made. The effects of the temperature dependence of the emissivity are analysed and an expression is given that allows one to evaluate the total measurement uncertainty for a given application.