Many radiometric measurements are aimed at determining the temperature of an object, not just its radiance. Over the years several ways to do this with various approximations have been developed, and the procedures for obtaining a temperature from different properties of radiation have been developed, analyzed, and used.
The temperatures are defined. Approximate equations and exact equations are given. Then, for a reasonable set of conditions the differences among the several radiometric temperatures and the true temperature are plotted.
14.1 Radiometric Temperatures
Several useful types have been defined. These include radiation temperature, brightness or radiance temperature, ratio temperature, distribution temperature, ratio-difference temperature and color temperature. Of late, the somewhat ambiguous effective temperature has also been defined and used (in different ways), particularly with infrared simulators.
It will be seen that radiation and distribution temperatures are functions of the average emissivity of the body, while radiance and ratio temperatures are strong functions of the spectral emissivity and spectral atmospheric transmission and vary over the spectrum. Each is the temperature of a blackbody that gives the same radiometric properties as the body in question.
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