By regarding the total ambient radiation falling on a greybody as an equivalent radiation of a blackbody at temperature TB and by using two standard reference plates, we are able to measure accurately the ambient radiation. In addition to the ambient radiation, there are two factors still affecting the self-radiation of a greybody, i.e., the emissivity ɛ and the truth temperature T. We point out theoretically that the emissivity could be determined by changing the ambient radiation. In this paper two simple methods are proposed for measuring the emissivity and good results are obtained for a variety of greybodies. These methods are not only practical in the laboratory but also in the field. The experimental results agree well with the data published by other investigators. After TB and ɛ are measured, the truth temperature T of the greybody can be obtained. Based on the theory presented here, we designed and produced a new infrared thermometer which can directly read out the truth temperature.
© 1986 Optical Society of America
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