Jan, your points about film make sense, so thanks for that.
I used Ilford SFX in daylight with a red filter, but the effect was
minimal (and there was no dimpling from the pressure plate).
However, the idea that Night Vision Goggles detect reflected the
energy of IR illuminators must be applicable only to short-range
equipment. The NVGs used by helicopter and fighter pilots and crews
must use a different technology as the illuminator would not have the
range to illuminate the sort of scenery you need to be able to see at
flying speeds (even helicopters).
Others have made the same point about cooled heads. The AIM-9L
(Sidewinder) uses a cooled head I believe. But the AIM-9G and
earlier heat-seaking missiles did not. I think that there is already
enough differential (from an engine) for such seekers and that
cooling merely assists in early and accurate detection and self-track
- ot also enables the missile to detect the different radiation from
other parts of the airframe so that a head-on detection and
self-track is possible.
BTW, the sound of these heat-seekers on a heat source is a very
exciting thing. The 9G makes a chirruping sound, while a 9L goes
into a sort of warble. The 9M goes into a high-pitched scream.
There must therefore be a crossover between heat that rises to the IR
wavelengths (such as the metal of an engine exhaust) and the IR
radiation from the atmosphere that is reflected as a cultural return
variously by different materials and organic compounds and that would
show up on IR-sensitive film. Am I on the right track?
BTW, even diesel engines show up on FLIR. It might be dangerous to
be near a recently run engine at night in a war zone...
Chris
Finally, I am assuming that IR film acts in a fashion similar to
the real-time sensors.
I think that's where the trouble starts, Chris.
The basic operation of ANY sensing medium depends on a differential
in energy levels. Chemistry-based film of all kinds, including IR,
is carefully designed so that it does not self-expose (well, too
much) if placed on the dashboard of a closed-up car in the sun all
day. Thus it cannot be used to sense hot objects, or it would be
impossible to economically ship and store.
The sort of detectors you referred to are artificially cooled during
operation so there is sufficient differential between their ambient
condition and the condition they are detecting. A detector that is
at 20 degrees C simply doesn't have enough energy differential to
detect human skin that is only at 30 degrees C.
Those "night vision" goggles you see in the movies and TV? They
contain IR illuminators. In effect, they shine invisible near-IR
light on the scene, and then detect its reflection. They DO NOT
sense the heat of human bodies.
Well, gotta go. UPS just delivered a package that is sitting in the
sun on my porch, smoking as though there were dry ice inside -- it
must be that new thermal IR film I ordered... hope I can expose it
before my body temperature does... :-)
--
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