Experimental validation of a pyroreflectometric method to determine the true temperature on opaque surface without hampering reflections

In the most common case of optical pyrometry, the major obstacle in determining the true temperature is the knowledge of the thermo-optical properties for 'in situ' conditions'. Here, we present a method able to determine the true temperature of objects from 500 degrees C up to 3000 degrees C when the emissivity is unknown and when there is not parasitic effect of surrounding radiation. The method is called bi-color pyroreflectometry and it is based on the assumption of identical bi-directional reflectivity distribution Functions (B.R.D.F.) for two different wavelengths (1.3 and 1.55 mu m). The diffusion factor eta(d), a key parameter of the method, is introduced to determine the convergence temperature T, that is expected to be equal to the true temperature T. Our goal is to verify the temperature measurement's accuracy for opaque materials. Validation of this method is based on: Comparison measurements with thermo-couple data. Comparison of eta(d) values determined by the convergence method and by a separate measurement of the bi-directional reflectance distribution function (B.R.D.F). Confirmation of single-value results with a measurement at a third wavelength. After introducing a theoretical model for pyroreflectometry we give a descriptions of the experimental set-up and present experimental validations of the present method. Finally, we discuss limitations for its application. The quality of the results demonstrates the usefulness of pyroreflectometry under circumstances where the emissivity is unknown. (c) 2009 Elsevier Ltd. All rights reserved.