Infrared Sensing Technology
Country: United States
Date: December 2006
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?
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
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.
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
Click here to return to the Engineering Archives
Update: June 2012