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

Abstract

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.