Temperature recovery of opaque bodies by thermal radiation spectrum: the use of relative emissivity to select the optimal spectral range

The approach based on relative emissivity was tested and developed using the experimental data. It was assumed that the medium separating an opaque body and measuring device was diathermic or nonradiating (it is characterized by its transmittance); radiation source emissivity and medium transmittance were unknown. Data on comparison of spectral radiances (spectral intensities), obtained within 220–2500 nm for the temperature lamps in the metrological laboratories of Europe, Russia, and USA were used as the initial experimental data. It is shown that the use of relative emissivity allows graphical interpretation for the solution to the initial nonlinear system of equations. In this case, the problem of determining the true temperature of the body by the thermal radiation spectrum in a graphical interpretation is reduced to the choice depending on relative emissivity at the desired temperature. It is shown that to narrow the interval, which includes the true temperature, the criterion was based on a change in convexity of spectral dependence of the relative emissivity in the process of desired temperature selection. The use of relative emissivity in a spectral range, where the Rayleigh—Jeans approximation is satisfied, allows unambiguous determination for the shape of emissivity dependence on the wavelength. The relationship for determination of the peak wavelength within the registered thermal radiation spectrum on the basis of data about the true temperature of the body and its spectral emissivity is presented.