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Re: [OM] Re Infrared images

Subject: Re: [OM] Re Infrared images
From: Paul Wallich <pw@xxxxxxxxx>
Date: Mon, 25 Sep 2000 08:39:21 -0400
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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