A new wavelength selection criterion for two-color pyrometer interfered with participating media

Two-color pyrometry is well established and widely applied to surface temperature measurements. However, its accuracy degrades significantly when the transmission path between the object surface and the pyrometer is full of high concentration participating media, which attenuates the surface radiation signal to the pyrometer. To improve measurement accuracy, a theoretical optimization wavelength selection criterion for two-color pyrometry working with the interference of a participating medium is established on the basis of the Plank's law and Wien's approximation. The closer to zero the criterion value is, the smaller the measuring error is. Therefore, the optimum choice of operating wavelengths combination for two-color pyrometer is obtained through inter-comparison of the criterion values. Evaluation of the practical applicability of the new criterion is performed by employing an analytical radiation thermometry model considering radiative attenuation and augmentation in participating media. Theoretical estimations confirm that the new criterion has good applicability and scientific quality considering two typical media ordinarily encountered in engineering applications: water vapor and water mist. This selection criterion not only provides solid reference information for the proper selection of wavelengths combination, but also helps one to better understand the fundamentals of measurement errors for two-color pyrometer interfered with participating media. The analyses in the paper provide the necessary theoretical supports for the design and application of a two-color pyrometer.