Pyrometry and Thermography

Herschel1 discovered the infrared spectral region of optical rays about the year 1800. Although the first applications for thermography devices date back to 1900, the field of pyrometrics took a different course of development. An exact definition of the two measurement methods shall not be made at this point. The following characteristics will serve to illustrate the differences between the two methods. Pyrometry is a method which allows measurements of temperature to be recorded from surfaces emitting temperature radiation also known as heat radiation or thermal radiation. These temperature radiations are recorded by a pyrometer, a “radiation thermometer” resulting in point like information. In contrast, when the information obtained is optically recorded as an entire scene ie. buildings, operational equipment etc. and displayed as a “temperature picture” this is known as thermography. A firm grasp of the difference between infrared photography and similar methods -which record only the reflected spectral portion of the optical spectrum (only in the near region of the infrared spectrum) and which generally do not permit any temperature intepretations of the recorded scene to be made-is essential to understanding this phenomena.