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Appendix A – Introduction to Thermal Imaging
Uncooled detectors are mostly based on pyroelectric and ferroelectric materials or microbolometer technology.
The material is used to form pixels with highly temperature-dependent properties, which are thermally insulated
from the environment and read electronically.
A.3 Atmospheric conditions and their effect of
Thermal Imaging.
Thermal imaging cameras can see in total darkness, through fog, rain and snow – producing a clear image in
which details can be discerned.
However, the distance thermal cameras can see is affected by existing atmospheric conditions. A thermal
imaging camera produces images based on the differences in thermal radiation that is emitted by the object in
question. Therefore the further this infrared signal has to travel from the object to the camera, the more of the
signal can be lost.
Based on this reasoning the attenuation factor, the ratio of the incident radiation to the radiation transmitted
through a shielding material, needs to be considered.
A.3.1 Humidity;
Humid air acts as a shield for infrared radiation, summer months usually have a higher attenuation compared to
winter months due to increased humidity levels. So even in good weather conditions, you will be able to see
further with a thermal camera in the winter than in the summer.
A.3.2 Fog, rain & snow:
Fog, rain and snow affect the ability of a Thermal imaging camera to detect objects. Fog, rain and snow are all
visible aggregates of water droplets which have a detrimental effect on the detection levels of thermal imaging
cameras.
In conclusion, it is impossible to state with any definite accuracy how far a thermal camera can see or how
much shorter the range will be in foggy, rainy or snowy conditions. The result is not only dependent on the
atmospheric conditions and the type of fog, rain and snow but it is dependent on the IR camera used and the
properties of the object in terms of its size, temperature difference of the object and its background etc.
A.4 Examples of Thermal Images
The following images show an example of a hot and cold subject, and how they appear when viewed
through a Thermal Imager when set to "Ironbow" mode (see section 1.2)
Operating Instructions
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