Temperature Estimation by Using Extended Tn Relation of Radiance for Thermal Radiation

In order to get the true temperature of an object in radiation thermometry, we have to correct the deviation of the brightness temperature from the true temperature by estimating the emissivity of the object or to cancel the effect due to the emissivity by some operational procedure. The method proposed in the present paper is basically based on the latter idea. The method uses the radiances measured in two partially overlapped spectral bands, in which the spectral emissivity of the object is approximately equal to each other. The extended Tn relation of radiance for thermal radiation is such that the radiance from the black body at temperature T observed in a spectral band and in a temperature range is given by aTn, where the factors a and n are constant and are different from one spectral band to another. When the object is at much higher temperature than the environment is, the true temperature of the object is easily estimated from the ratio of the radiances at the spectral bands. When the temperatures are similar, we get the true temperature by numerically solving a simple algebraic equation derived from the radiances by using the extended Tn relation. The validity of the method was confirmed by experiments for objects with various emissivities. The comparison of the results withthose by other conventional methods showed the superiority of this method.