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I've long wondered this.
Back in the early days of low/no visible light vision everything was thermal imaging and rather blobby. As you see in films like predator or with the images you get of heat sources in civilian tech (as in house thermal reports and so forth). This is understandable given you are viewing a radiating em source that affects material around it.
But then there seemed to be a sudden change to higher res 'green' image intensifiers. The image was much more like normal vision, no blobby smearing of objects, for example.
I thought initially it was not thermally based but an intensified viewing of visible light (hence image intensifier) - but heat sources still show up and are noticeably brighter. So clearly there is still a thermal component to the technology.
So what happened? Why is modern thermal imaging so much clearer, what tech changes happened and how come the increase in resolution was so sudden? It seems, unlike most tech, there was no gradual increase in accuracy but a singular step change.
I have, at the back of my mind, some recollection of near and far IR being used. But if so, why is one better than the other, and what prevented us from using the 'better' one first?
oh, and why green?
The human eye can see more shades of green which is why they use that (or so I've been told). Would that also affect the clarity?
i know thermal imageing is blocked by glass
the challenger togs system is useles aginst glass, so hide your tanks behind glass sheets
I believe it was the invention of the Charge Coupled Device which caused the change. The CCD is a very sensitive device capable of sensing individual photons, and can detect light over a broad range of frequencies. So it will amplify existing light and also any infrared light (heat sources). And VLSI technology (used for making integrated circuits) allows them to miniaturise the CCD so that you get high resolution.
It's the same technology that allows today's megapixel digital cameras.
I suspect the heat sensing of the 'green' vision is because the hot objects also emit more IR which is what is being picked up.
Thermal imaging does work differently from the IR amplified type.
Oh and green because that's the wavelength the eye is most sensitive to.
Infrared imaging was popularized using Image Intensifiers. Subsequent portrayals referred back to those results. IR is heat and as such it takes time for the heat to change. An IR image had to build up and then dissipate. In the process it would also spread to the surrounding area of the image. Lenses were Germanium Meniscus Lenses with a silvery reflective appearance. Married to the front of a TV camera tube, what was visible came from the green phosphors of the Image Intensifier anode. One photon into the intensifier, one-hundred photons was emitted from the green phosphors.
The use if CCD imaging devices did not require Image Intensifiers -AEHill
An image intensifier tube is a vacuum tube device for increasing the intensity of available light in an optical system to allow use under low light conditions such as at night, to facilitate visual imaging of low-light processes such as fluorescence of materials to X-rays or gamma rays, or for conversion of non-visible light sources such as near-infrared or short wave infrared to visible. - http://en.wikipedia.org/wiki/Image_intensifier
Charge couple devices, the same things that give us digital cameras. They can be made really small and each one is a single pixel on the image. They were only developing them when I was in college, but everyone knew they were going to be the next big thing.
Should have read the backlog. I gave the same answer about two years ago.