Apparent Temperature Patterns Superposed on Thermal Infrared Images and Their Removal
Department of Electronic Engineering, Faculty of Engineering, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma, 376 Japan
A thermal infrared image is a visualized image of the thermal energy radiated from an object. Thermal radiation energy is dependent on the absolute temperature and the effective emissivity of an object, so that a thermal infrared image does not give the temperature distribution of an object but, rather, is a superimposed image of, so to speak, the temperature pattern and the emissivity pattern. In other words, a emissivity pattern is an apparent temperature pattern superimposed on a true temperature pattern. However, this paper points out that a thermal infrared image obtained with a sensor having an instantaneously large field of view, like a remotely sensed image, has additionally a third pattern due to the size of the field of view superimposed and that this appears as an apparent temperature change on the thermal infrared image. Moreover, the paper stresses the fact that in order to obtain correct information on temperature, it is necessary to remove these patterns and, at the same time, points out that these can be removed if effective use is made of visible, multispectral images.