infrared cameras seeing though walls?

[ivymike]

okay, I'm sure everyone has seen movie footage of infrared cameras seeing people through concrete walls and the like. I can't imagine that concrete is transparent to infrared light, and I expect it would have to be for that trick to work... so what's the deal? is that stuff all fantasy, or am I missing something?

 

[JAE]

The firm I used to work with had an infrared camera used for analyzing leaks, roofing, etc. We once took it into an existing building and pointed it up at the ceiling - we could see the 2x wood roof joists through the 1/2" gypsum sheathing due to the cold air outside reflecting inside.

We could also see wall studs.

It picks up moisture (due to the colder temperature of wet things) and they used it primarily to look for leaks and wet spots beneath roofs.

Pretty sure it cannot "see" through block or concrete walls unless there is some type of thermal gradient on the surface of the wall.

 

[IRstuff]

Usually, what you "see through the wall" is something that's actually in contact or proximity to the wall, and it's affecting the local temperature. Would make my job sooo much easier if IR could get through walls, and dirt, and water, etc.

TTFN

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[ivymike]

'bout what I figured... in the movies you can see people walking around in rooms, etc. I only brought it up because an article I read a couple days ago said that US Ranger dogs were fitted with "doggles" that would let them see humans moving around on the other side of concrete walls...

 

[Ron]

I have an infrared camera. If you have a concrete wall, it would be difficult to "see" people behind the wall, unless the wall were very cold. People can be "seen" behind stud walls and as JAE noted, studs are usually clearly evident when viewed at the right time of day.

An IR camera is only a fancy thermometer, albeit a very expensive one!

 

[ivymike]

yeah, so when people move behind the wall, the image should stay put until the stuff in between the people and the camera cools/heats, right? ..and if someone keeps moving, there would never be an image, except perhaps something representing the local thermal conductivity of the in-between material?

 

[Ron]

Well, sort of. If the person does not touch the wall, the movement can be followed. If the person touches the wall, it gets a bit fuzzy.

One of the demo tricks I use is to have someone put the palm of their hand up on the wall. I wait about 10 seconds after they have pulled their hand away and then "shoot" the wall. The handprint is still there. Good "ooh/ahh" factor.

 

[evelrod]

I watched that movie, Isaac. I thought it was "microwaves" that the Feds were using to "see through walls"...

There is a K-9 unit at the Marine base and there have been several articles in the local paper about the dogs and their training. Several practice jumps have been done here at Skylark Field with the dogs. They never say when they are going to do practice jumps or I would go over and watch...it's only a mile away!

Rod

 

[JStephen]

In the past, I have done some photography using infrared film. One of the things I found when reading online forums on the topic was that some opague fabrics are more or less translucent to infrared, so under the right conditions, you can photograph through clothes to some extent. (I think this was more feasible with digital IR than with the film.)

And just an FYI, the "infrared" spectrum covers a vast part of the spectrum. The IR used with infrared film is that part of the IR spectrum right near visible light. That used in detecting heat is way way down the scale of IR, so it's two quite different concepts. The IR film is always working with reflected IR light, never IR emitted by the subject.

 

[IRstuff]

The spectrum that includes "IR" photographic film is in the range of 800 nm to 1500 nm. Many plastics and polycarbonates are transparent in this region, including most sunglasses and the color filters on CMOS cameras. That's why camcorders can "see" in low-light conditions, but without color. The range from about 800 nm to about 1000 nm is regarded as "near" infrared (NIR), although "short" wavelength infrared (SWIR) overlaps, 900 nm to 2500 nm.

Thermal cameras are either 3um to 5um, medium wavelength IR (MWIR), or 7um to 14um, long wavelength IR (LWIR), at least, those that are used in most heat imaging applications.

There are also cameras that can image out to 50um.

The last 3 categories of infrared cameras usually require cryocooling, although there are LWIR camers that are uncooled and can operate at room temperature. The cameras that image beyond LWIR generally require liquid helium cooling.

Past that, we start running into RF systems, millimeter-wave (MMW) and terahertz (THz). Some of the body scanners in airports are either MMW or THz.

MMW tends to do better in penetrating walls.

TTFN

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[JAE]

I seem to remember seeing some old comic books that had an ad for some type of "see through walls" glasses. The guy wearing them was looking at a woman and his eyes looked really frazzled. He looked like he was really in shock or jazzed up. Not sure why.

Maybe they were dangerous...

 

[Ron]

...or maybe the girl was that good looking and he was an engineer!

 

[IRstuff]

Those glasses were supposed to be "x-ray." Unfortunately, my mom got rid of ALL my old comics, otherwise I'd still be able to buy a pair.

TTFN

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[VEBill]

...old comic books that had an ad... (for x-ray glasses)

Many many years ago, a school friend actually ordered a pair of those x-ray glasses from the famous comic book advertisement. When it finally arrived, he was very disappointed. He asked me if I could guess the 'technology'. I immediately guessed, "Are the lenses simply made with chicken feathers?" - Correct.

There, I just saved you guys $2.99 plus S&H.

 

[ivymike]

I bought a scott eagle 6 imager to play with. It sees studs in walls, drywall srews, and footprints on the floor, but it definitely cannot see a moving person through a wall. Can't really see a dog behind a bush very well.

 

[jraef]

There are (or at least were) "cameras" that could see through solid objects, but not IR from what I wss told. My late uncle was a researcher for Edwin Land (as in Polaroid Corp.) on a project for the DOD back in the early 1970s that was supposedly a way to see through solid objects using what he called "radar" (I was too young to question him on that but my father said it wasn't). Land of course did a lot of work with light and IR, so maybe that's how the rumors got strarted.

It apparently worked so well they wanted to see just how good it could be. They sent my uncle to Egypt for 3 months to test the effectiveness of their system by trying to "see" the known chambers in the Great Pyramid of Cheops. They didn't, but he had a lot of fun trying.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
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[msquared48]

I heard that they used to have these cameras for rent at Howard Johnson's.

Mike McCann
MMC Engineering

 

[IRstuff]

There are lots of radars that can penetrate solid materials. Probably the most familiar is Ground Penetrating Radar (GPR). It's often been used to determine location of buried objects, and the US uses them for buried explosives detection. At one point in time, the US was supposedly interested in GPR as a means of seeing behind walls, as part of their initiative to augment the weapons available to each soldier.

TTFN

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[unclesyd]

This might be of interest.

http://www.physorg.com/news/2011-10-radar-technology-real-time-video-solid.html

 

[jraef]

Interesting.
Not exactly inconspicuous or robust, and the output is not exactly definitive. But if you look at the earliest versions of radar, it all started from seemingly innocuous radio signal glitches that someone figured out was an object. Once the concept was known to exist, great minds went to work on it and now we have very clear imagery and very small packages. I would expect this will develop in a similar fashion.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376