At 7:51 AM +0200 9/25/00, Chris Barker <imagopus@xxxxxxxxxxxxxxxx> wrote:
Now I am confused with this thread...
Surely the difference in heat is what is detected by an IR sensor.
Military applications (the only ones that I am familiar with) are
based on being able, for instance, to detect where vehicles are
hiding in woods. Depending on the time of day, and crossover
etc..., you can find vehicles that have been running their engines.
Likewise, an IR seeker on a missile follows a heat source because it
emits radiation in a certain range of wavelengths.
The military IR detectors I'm familiar with for detecting vehicles or
people relied on cooling (usually peltier solid-state). The really
fancy (astronomical) ones use liquid nitrogen or even liquid helium.
Noise-canceling at ambient temperature is possible but really ugly.
The Forward Looking Infrared (FLIR) sensor in the aircraft that I
flew could show you differences in reflected heat certainly, but the
exhausts of a pair of turbofans in a Tornado was not reflected heat.
Since the metal in contact with the exhausts tends to glow a very
dull red, the gas itself is probably well up into the temperature
range where even IR film could see it. (Historical note: when tanks
started using gas turbine engines instead of diesels, they became
much more visible on IR until better cooling and airflow could be
designed.)
--
Paul Wallich pw@xxxxxxxxx
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