Factors Affecting Thermal Imaging

Infrared Energy

Is similar to visible light except it can not be seen or sensed.  The wavelength is between 0.7 and 1 billionths of a meter.  Like light it will not pass through a solid object but it can be refracted, absorbed and emitted.  Your television, VCR, sound system, satellite system  remote controls uses Infrared energy to send signals to your favourite electronic device.
Infrared Radiation is emitted from all objects by vibrations and rotation of atoms and molecules.  The higher the temperature of the object the greater is the energy, this is what is detected by the Infrared camera.

Density

(Mass per unit of volume of a substance)
A compressed section of an article will have different colour pattern than the main area of the article
A higher density material such as high strength steel will radiate heat differently that a less dense form of steel.  The image for hard wood (oak) will not be the same as for a soft wood (pine).  Knots covered by paint will be visible. (Emissivity)
A crack, dowels, nails, weld joints, etc. or abnormality in the object will be displayed even if not visible to the eye.  A joint no matter how skillfully finished will have a different temperature than the main object.  Material used to join / repair an item will present an image different than the base item.

Moisture

The presence of a liquid in any area of the object will display a unique colour pattern different from dry sections, normally cooler.
Each type of dampness created by the combination of materials may have a unique colour pattern on the image, water will have a different colour than oil
The liquid or other substances may not necessarily be present on the surface, it could be concealed behind paint or other covering but it would affect the colour image.
A section of material that had been subjected to moisture and subsequently dried will likely display different colour characteristics than virgin material
If there is air infiltration or escape, moisture will accumulate on surfaces at the site of the air movement, if there is moisture there will be mould.  Moisture and wood this is the favourite dinning site for termites.

Background Material

The supporting structure behind the visible object may appear in the image as the temperature, density and depth of the support or content of the article will be different than the containment material.
The level of the contents of a tank will be shown as the temperature of the container above and below the level of the material will vary.
Pipes and wiring behind the view area may be visible on the image
The presence of water behind the exterior material may be indicated particularly if the water is in contact with exterior material.

 

Ambient Temperature

The temperature of the surrounding air will affect the images of the object on the display.  However the primary objective is to test the variation of the temperature of the items being scanned.
The object at freezing temperature will have a different colour image than the same object at boiling water temperature.  The object is to determine the temperature difference with other items in the same ambient temperature or other parts of the subject.  It is the temperature difference that will identify areas or conditions of concern.
 

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