Understanding the Thermal Imager

One of the most common misunderstandings of technology I see on many of these paranormal themed reality shows has to do with how the data gathered by the thermal device is interpreted.

Below is a thermal image taken from a quick Google search:

Image from the Blog, “Ghosts and Paranormal”

On the right side of the image is a data range indicating the heat radiating from the captured object.  In this case, the range is from 23 degrees centigrade to  11 degrees centigrade.  It is important to note this scale because images appearing on the thermal device that may seem much warmer than their surroundings may, in fact, be much closer in actual surface temperature.  Again, referring to the picture above, the front of the house seems much warmer than the roof, as indicated by the orange hue as compared to the purple hue of the roof.  However, by looking at the scale, we can tell that there is really only about a 3 degrees centigrade difference  (which is only approximately a 8 degree difference — 18 degrees centigrade is about 64 degrees Fahrenheit compared to 13 degrees centigrade which is about 56 degrees Fahrenheit).

Image from Vorpral.net

Similarly, this image shows a dog lying on the ground.  Notice the scale, however.  At most, this thermal device is measuring the captured data on a 9 degree Fahrenheit span.  This means that even though the dog may seem much hotter than the floor based purely on the image, it is no more than 9 degrees warmer.  Applying the scale to the picture, we can see that the “dog” may really only be about 5-6 degrees warmer than its surroundings.

The most important aspect of analyzing collected data is understanding how to read the data.  Next time you are watching one of these reality shows and the investigators come across a thermal hit that seems to be “on fire” compared to the surroundings, look to see if they’ve included the scale in the shot, and take note of how much warmer the object or area is compared to its surroundings, rather than relying solely on the color distinction.


One response to “Understanding the Thermal Imager

  • Nate

    This is definitely a very important aspect of using thermal evidence. In many cases I feel that it can break the case, I can think specifically of an episode of Fact or Faked where they were investigating a theater where somebody caught some supposed footage of a ghost. Later in the investigation somebody noted a “hot spot” on a specific seat in the theater. They went nuts. Then another investigator walked into the frame of the thermal camera and the “spot” just “disappeared.” Surprise, surprise. I would predict that there hotspot was within the normal variation of ambient temperature based on the properties of the reflecting material. When a person walked into the frame, presumably much warmer than the ambient temperature of the seats, the warm spot was lost in the large jump in the scale of the thermal imager.

    That is not to say impressive evidence has not been caught with thermal imagers, as it definitely has. In the video below beginning at approximately 0:40, a figure enters the frame, shuffles around a bit, then leaves the frame. It is later seen peeking back into the frame. It would be all to easy to dismiss this as a trespasser or a crew member in the wrong place at the right time. The scale of the thermal imager indicates a high temperature of approximately 45 deg F. This would preclude the figure from being a flesh and blood human, as the scale would have gone much higher.

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