A New Method for Temperature Distribution Measurement Using Multi-Spectral Radiance

Abstract

In this paper, a new method for measuring the temperature distribution using multi-spectral radiance is described. An optical thermometry for small hot area, such as a welding point, is different from an ordinary method. Because of the sharp temperature distribution, it is impossible to assign it a single valued temperature. A measurement of the temperature distribution is essential.
The principle of this method is as follows. The field of view of a radiant sensor covers the target, and the radiant energy from it is measured with multi-wavelengths. The temperature distribution in the field of view can be calculated by the measured multispectral radiance. The temperature distribution x(T) is defined as dS/dT, where S denotes an area of the temperature T. Relation between the spectral distribution of the radiant energy and the temperature distribution is expressed as the 1st kind Fredholm type integral equation. To solve the integral equation, the author proposes an iterative method using a Dynamic Programming approach.
Computer simulation is carried out to examine this algorithm, especially to examine how the spectral range and emissivities affect the measuring accuracy. In case of a smooth x(T), this algorithm provides strongly convergent result.
The validity of this method is examined by the following measurement. The temperature distribution of a globar is measured and it is compared with the distribution calculated from the observed radiant energy. Good agreement is obtained between the both distributions.
This method proposes a unique standpoint in the optical thermometry to utilize multispectral radiance.