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This work is aimed at improving metrological characteristics and expanding the areas of application of optical thermometry of opaque objects, including the method of two-color compensative pyrometry with an apriori averaged adjustment previously developed by the authors. A nonlinearity equation has been obtained that connects the nonlinearity coefficient of spectral distribution of directional emissivity on an average wavelength of the registered radiation with a value of spectral directional emissivity on one of boundary wavelengths via the measured brightness temperature on three wavelengths. It has been established that the number of numerical solutions of the equation at various qualitative and quantitative characteristics of spectral distributions is from 1 to 3. To determine a correct solution, analytical and algorithmic methods of its identification have been proposed. On the basis of the equation, linear, two-range, and parabolic methods of determining spectral directional emissivity have been developed. It has been established that the methodological errors of temperature measurements by the two-range method are 5–7 times lower than the errors of the linear method. For significant nonlinearities, the parabolic method errors are 1.13–1.24 times lower than the linear method errors. In this case, for the two-range method, the combined errors for two-color compensative pyrometry are lower than the errors for spectral ratio pyrometry and for energy pyrometry 110 and 7 times respectively. [ABSTRACT FROM AUTHOR] more...

The influence of the optical characteristics of multicolor thermometry on its methodical and instrumental errors was investigated and, on the basis of the investigations performed, a new direction of symmetric-wave multicolor pyrometry of radiation, including linear and universal thermometric technologies, has been developed. It is shown that, in the case where the spectral distribution of the radiating capacity of a body is linear, the methodical error in determining its temperature by the method of linear symmetric-wave pyrometry of radiation is close to zero and is practically determined by the discreteness of the selection of temperatures of this body. The errors in measuring the temperature of the majority of materials, e.g., tungsten, by the method of linear symmetric-wave thermometry are 9.1-25.0, 5.9-6.8, and 2.4-3.3 times smaller than those given by classical energy, spectral-ratio and polychromatic pyrometries of radiation. The universal thermometry method proposed allows one to eliminate the methodical error, predominating in optical thermometry, in determining the temperatures of bodies with different linear and nonlinear spectral distributions of their radiating capacity. The residual instrumental error given by linear and universal symmetric-wave pyrometries of radiation of a body does not exceed the error in measuring its initial monochromatic radiation temperatures, i.e., 0.2-0.5%. [ABSTRACT FROM AUTHOR] more...