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Old 09-07-2009, 06:04 PM
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It is a simple demonstration of the greenhouse effect. Glass is transparent to visible light but opaque to middle and long wave IR. Light enters a vehicle or room through glass and is absorbed by the contents which then re-radiate most of the energy in the infrared. The IR can't penetrate the glass to get out so the temperature gets higher and higher. Eventually the glass itself will get as hot as the contents and becomes visible in IR itself.

If you kept the space blanket away from you so it stayed at air temp it would always block your IR. Of course it shows up like a spotlight on radar.

Interestingly, high quality optical glass is transparent to short wave infrared. This is the color just below deep red on the spectrum. So infrared photography is possible using a visibly opaque filter. You can use it to distinguish between healthy plant material and stuff that has been cut for camouflage purposes. Skin is somewhat transparent to it so you can photograph your veins right through your skin.

There was a fuss raised about this a while back because some digital video cameras were using IR to help out in low lighting situations and some clothing was actually transparent to those wavelengths.

Last edited by TMcArthur; 09-07-2009 at 06:12 PM..
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Old 09-07-2009, 10:22 PM
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So if we get air conditioned glass bubbles (like hamsters use) we're ok? We can just roll away ! Habitrail anyone? Sry,couldn't resist !
Old 09-07-2009, 11:10 PM
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Quote:
Originally Posted by Otto View Post
I have heard that a suit made of mylar or tin foil will defeat any heat signature that a FLIR would use.
Now we know the real purpose for the Tin-Foil hats!!!!

On a serious note, I cant remember what show it was, but apparantly there are some sniper ghilli suits that mask IR, and they where doing a test of them on some show showing how they work...

It might have been future weapons or something, i dont remember..
Old 10-12-2009, 02:42 PM
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on the topic of space blankets, yes they do partially block ir from your body but you would need to make sure NO part of your body is touching the space blanket, otherwise there will be a transfer of heat from your body to the foil making you stand out, also after being under it for a bit it will start to show on ir cameras.
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Old 10-19-2009, 10:27 PM
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TMcArthur wrote:
Quote:
It is a simple demonstration of the greenhouse effect. Glass is transparent to visible light but opaque to middle and long wave IR. Light enters a vehicle or room through glass and is absorbed by the contents which then re-radiate most of the energy in the infrared. The IR can't penetrate the glass to get out so the temperature gets higher and higher. Eventually the glass itself will get as hot as the contents and becomes visible in IR itself.

If you kept the space blanket away from you so it stayed at air temp it would always block your IR. Of course it shows up like a spotlight on radar.

Interestingly, high quality optical glass is transparent to short wave infrared. This is the color just below deep red on the spectrum. So infrared photography is possible using a visibly opaque filter. You can use it to distinguish between healthy plant material and stuff that has been cut for camouflage purposes. Skin is somewhat transparent to it so you can photograph your veins right through your skin.

There was a fuss raised about this a while back because some digital video cameras were using IR to help out in low lighting situations and some clothing was actually transparent to those wavelengths.
You may have just answered a question I have had for a while now.

A few years ago our fire department purchased a thermal imager. I was playing with it in my office and was walking towards a solid glass door when I saw my reflection in the imager. This totally blew my mind, but now sort of makes sense. Can you explain this further for me since it appears you have a pretty good handle on the subject?
Old 10-19-2009, 10:42 PM
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Quote:
Originally Posted by Hick Industries View Post
The easy solution is a emergency sleeping bag made of alluminized foil. It works to keep you warm by reflecting the IR heat back to you. While many other things can work, that one is cheap and light and designed to reflect IR.
thats all I need running around the woods dressed like a 6' tall silver worm...
Old 10-19-2009, 10:46 PM
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So explain to me how are you going to know someone is using FLIR to watch you?
Old 10-20-2009, 09:31 PM
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Most police helicopters are FLIR equipped now. Every single aircraft from Border Patrol/Customs Border Protection is so equipped.

Outside temperature will have considerable impact. Concealing yourself in the snow will be difficult. Your heavy foot prints may even show at times.

Does not work against water of any temperature. Submerse yourself and you may elude abservation... for as along as you can hold your breath or use a breathing tube.

Like a lot of techno gadgets, it depends on who is monitoring them, and their knowledge of the terrain, patterns, etc. This is one reason why SOG used veteran Recon men as "Covey Riders" on OV-10 and observer aircraft. They knew the terrain from the ground up.
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Old 10-21-2009, 03:52 PM
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I cannot remember the show but it was one of those "Craziest Police Chases" a guy bails from his car after a chase and takes off into the woods. He hides in some evergreen trees and the FLIR abosultey shows nothing. It had to do with the fact that evergreen trees have less of a heat signature or something. Can anyone verify?
Old 10-22-2009, 09:53 PM
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Quote:
Originally Posted by pullpin View Post
I cannot remember the show but it was one of those "Craziest Police Chases" a guy bails from his car after a chase and takes off into the woods. He hides in some evergreen trees and the FLIR abosultey shows nothing. It had to do with the fact that evergreen trees have less of a heat signature or something. Can anyone verify?
I think I saw that same show yesterday. I think it was "Alaskan State Troopers." If it was the same show you're talking about, he may have defeated the handheld FLIR, but he may also have just ran out of the woods before they started looking for him. They never caught him on the show.
Old 10-22-2009, 09:57 PM
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...aluminum foil, plus it has the advantage of keeping alien voices from penetrating your skull (j/k)
Old 10-23-2009, 03:22 PM
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FLIR can only detect heat differential of an object compared to it's surroundings. It cannot "see through" anything. Any barrier between you and the FLIR will block it from seeing your heat, until the barrier warms up and reaches the same temp as you. This happens when you touch the barrier. However, usually the barrier is easily seen by other means, visual, radar, whatever. Having the barrier stand off from your person will slow it's heating up, but if the barrier encloses a space around you completely, it will eventually heat up. The spruce limbs mentioned earlier will block your heat signature due to their density, the lower limbs may warm up but the ones above them will not any time in the forseeable future. BTW, a fire will create a heat plume visible to IR in addition to visible smoke. Even without smoke, like fuel tablet fires, there is a heat plume, however small it may be. Best is to minimize the difference between your heat and the surrounding area heat.
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