Evaluation of angle dependence in spectral emissivity of ceramic tiles measured by FT-IR

Abstract

Ceramic tiles are widely used for building walls. False detections are caused in inspections by infrared thermography because of the infrared reflection and angle dependence of emissivity. As the first problem, ceramic tile walls are influenced from backgrounds reflection. As the second problem, in inspection for tall buildings, the camera angles are changed against the height. Thus, to reveal the relation between the emissivity and angles is needed. However, there is very little data about it. It is impossible to decrease the false detection on ceramic tile walls without resolving these problems; background reflection and angle dependence of emissivity. In this study, the angle problem was investigated. The purpose is to establish a revision method in the angle dependence of the emissivity for infrared thermography. To reveal the relation between the emissivity and angles, the spectral emissivity of a ceramic tile at various angles was measured by FT-IR and infrared thermographic instrument. These two experimental results were compared with the emissivity-angle curves from the theoretical formula. In short wavelength range, the two experimental results showed similar behavior, but they did not agree with the theoretical curve. This will be the subject of further study. In long wavelength range, the both experimental results almost obeyed the theoretical curve. This means that it is possible to revise the angle dependence of spectral emissivity, for long wavelength range.