Principles of the four-point thermographic measurement of the surface temperature and emissivity of glossy materials

The emissivity and surface temperature of glossy materials are measured in IR thermography by covering the surface with a material with the known emissivity. The quantities can be, however, determined without using materials with the known emissivity. IR radiation is reflected from the measured glossy surface and a thermographer detects such reflection.
This paper discusses the measurement of the surface temperature and emissivity of glossy materials which are used in external structures of the buildings - for instance, windows, light external walls or tiles. A four-point method is proposed for a more accurate determination of the surface temperature and emissivity of glossy materials. Results of successful laboratory and field tests of the method are presented.