Physical Aspects of Infrared Thermography

Thermography in the widest sense of the term can be defined as the recording of temperature. In a similar way the well known rotating drum which records the air-temperature can be thought of as a thermograph. Indeed, such an instrument is often combined with a barograph and/or a hygrograph. However, nowadays the term thermography is mostly used in a narrower sense for a method of forming an image (the thermogram) of the temperature distribution over the surface of a body1 and this is achieved by using the radiation emitted from the surface of the body. Some authors call this tele-thermography to distinguish the method from contact thermography in which the thermal sensor is in direct contact with the body (eg liquid crystal thermography).2 In (tele-) thermography we may distinguish: 1. Infrared thermography using the infrared radiation emitted by the surface of the body at wavelengths between 0.8 μm and 1 mm. 2. Microwave Thermography using the microwave energy emitted by the body at wavelengths between 1 mm and 1 m.3