Re: IR Scan Of Mystery Jet Reveals Pulse Detonation Engines?


Message posted by lone wolf on June 28, 2004 at 12:26:34 PST:

You can get thermal imaging cameras from $4k to $10k.

However, there are much cheaper ways to take IR photographs.

One is to use Macophot 820c and a red #25 filter. This set up has response to about 900nm. This qualifies as near IR, but you can see some IR effects in the photos. Green foliage looks white, tinted glass is clear, etc. It's about $9 a roll and needs to be delevoped by someone who knows what they are doing. The film processing is standard, but the tanks need to be IR proof. The film has to be loaded and unloaded with a change-bag, placing the film canister back into the black plastic container from the manufacturer. A roll of Macophot 820c will get fogged otherwise. Focusing is another story since the IR light will not be in focus with the visible light. Some stop down the lens a bit to increase the depth of field, but since you will be focusing at infinity in most cases, that trick doesn't help much. Macophot 820c is extended red film, not just IR. Unlike the competition (Ilford SFX for example), the Macophot 820c grain is extremely fine. With the red #25 filter, the film should be used at ISO 50 to maybe ISO 25.

Another way to see IR is with a B&W CCD. Don't be fooled by cameras supplied with IR LEDs. Those leds only go 30ft or so. What you want to do is see heat sources. A supercircuits PC164C will do the trick, i.e I have photographed soldering irons in complete darkness. However, to see an object far away is another story. Remember that the light grasp is inversely proportional to the square of the magnificaion. In English, twice the magnification means 1/4 the light, so after a while you can't get enough light to get above the noise floor of the CCD. I believe the Sony HAAD CCD has resonable response to about 2um. Thermal imaging goes as low at 10um.

Night vision equipment has IR sensitivity as well. However, NV is subject to the same laws of light versus magnification. If you expect to see the bird flying in the air from 10 miles away with NV, forget it. I don't believe 3rd generation NV is that good. [I haven't used anything better than gen3, though I believe they are up to gen 5.] Now you can see a dot moving around with NV. but what exactly have you discovered?

To spot targets on the ground, you can use either the Macophot 820c or Kodak Portra 400BW. Doing time exposure with the Macophot can find a hot spot, though I never found a hot spot that didn't have some visible light associated with it. I'd have to set up an experiment to see if an IR source by itself can be detected. The Kodak Portra 400BW does not have IR response, but it does have an interesting feature in that it has 5 stops of exposure lattitude. In English, this means that it can be overexposed without the light areas blooming. I did a few shots around the ET highway and found nothing really new, but did confirm areas at are lit but hard to see at night, such as Papoose Mountain. Shoot the Portra 400BW at ISO 50 or 25. This film needs to be developed in a color C-41 process.

If you experiment with IR, note that items such as IR LEDs are narrowband devices. That is, you get a spike at the wavelength stated in the datasheet. A hot object obeys the laws of black body radiation, which means it has a long exponential tail in its spectrum. Thus if the peak is at 20um, there may be enough detectable IR at the 2um level.

Now if you really want to see a bird in the air, I'm convinced the best you will ever do is get a, pardon my French, silhouette against the night sky using night vision. I've done this with both a Pavehawk helicopter and C130s, though in the case of the C130 I had some moon light to get the body illuminated. The Pavehawk silhouette was just amazing to see. Incidentally, the tail rotor hub was just glowing from heat. This was done with gen 2 Russian gear.


In Reply to: Re: IR Scan Of Mystery Jet Reveals Pulse Detonation Engines? posted by Chris_H on June 28, 2004 at 9:57:40 PST:

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