COMPARISON OF EMISSIVITY MEASUREMENTS USING AN INTEGRATING SPHERE REFLECTOMETER AND A LASER POLARIMETER ON SURFACES WITH VARIOUS DEGREES OF ROUGHNESS

Achim Seifter, Konstantinos Boboridis, Andrew W. Obst

Abstract

Laser polarimetry has been used for years to obtain normal spectral emissivity measurements on pulseheated materials. The method is based on the FRESNEL equations that describe reflection and refraction at an ideally smooth interface between two isotropic media. However, polarimetry is frequently used with surfaces that clearly deviate from this ideal condition. Questions arise with respect to the applicability of the simple FRESNEL equations to non-specularly reflecting surfaces. On the other hand, reflectometry utilizing integrating spheres provides a measurement of the hemispherical spectral reflectance for normal incidence, from which the normal spectral emissivity can be derived, regardless of surface texture. In a first effort to explore the limits of polarimetry in terms of surface roughness, room temperature measurements were performed on a number of samples using both an integrating sphere reflectometer and a laser polarimeter. In this paper, the two methods are briefly described and the results of the comparison are discussed.

Keywords

emissivity, integrating sphere, polarimetry, reflectance, reflectometry, rough surfaces, roughness

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DOI

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IMEKO TC

TC12 - Temperature and Thermal Measurements

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