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Name: Sharon
Status: Educator
Grade: 9-12
Location: CA
Country: United States
Date: December 2006


Question:
We watched a television program showing a CIA agent using what appeared to be infrared technology to see the body heat patterns of human beings inside a metal shed while he was standing outside the shed. Does this kind of technology exist?



Replies:
Hi Sharon

Infrared sensing certainly does exist and it can image a human form just fine. the situation you describe seems a bit unlikely, however. The IR sensor would be looking at the metal shed and would record temperature differences on the metal itself. If a heat source (a human) were sufficiently close to the metal wall being observed, then a temperature difference could be detected. However, if the heat source was farther away from the metal wall, the temperature difference would be spread out over the metal surface. Think of it as being very much out of focus. Furthermore, depending on the thermal conductivity of the metal, the metal wall would want to smear out the temperature difference in an effort to make the whole wall the same temperature, further obfuscating the image. I suppose if someone were sitting with their back against he metal wall it could be detected, but move away more than a few feet and detection would be unlikely. Hope this helps

Bob Froehlich


Those things are exaggerated regularly on TV. There can be microwave or millimeter-wave vision through uncluttered non-metal walls. That would look similar, and maybe somebody has it. But thin aluminum foil, the paranoid's favorite, would stop all that. Unless said persons were leaning right against the wall and warming it up. Even then it would look more indistinct than your TV show probably showed. So heat-vision of walking people through metal walls is out. Only X-rays, gamma rays, and maybe other hard radiation could go through typical metal sheet.

Jim Swenson


Infrared imaging depends upon the temperature difference between the target and its surroundings (or some other reference temperature). The image of objects, separated from the detector by some shield (such as a metal shed) will become more diffuse because the infrared radiation will be conducted away by heating the metal wall. So hotter/colder objects on the other side of the shield will be less distinct. A more clever CIA agent would use a sensitive highly directional microphone to detect the sound of breathing and hearts beating.

Vince Calder



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