How does night vision show where the ground has been dug up before and able to detect recent changes such as patch up work to a wall or something similiar?
I’m no expert, but I don’t think light-intensification systems can detect those. An infrared system, though, is able to detect minute changes in temperature. I’ve seen helicopter-mounted FLIR video that showed where a guy was hiding inside of a building because he was leaning against the corrugated steel wall and heating it with his body.
Night Vision technology consists of two major types: image intensification (light amplification) and thermal imaging (infrared). It’s the thermal imaging that can do this.
From How Stuff Works: “A really amazing ability of thermal-imaging is that it reveals whether an area has been disturbed – it can show that the ground has been dug up to bury something, even if there is no obvious sign to the naked eye. Law enforcement has used this to discover items that have been hidden by criminals, including money, drugs and bodies. Also, recent changes to areas such as walls can be seen using thermal imaging, which has provided important clues in several cases.”
Wholesalers-direct says the exact same thing, word for word I think about 3 sentences from the bottom of there huge page.
I also watched a show on TV where investigators used night vision to find where a man buried his wife in the backyard.
Having fooled with an old set of “active” night-vision goggles (which require an IR light source, rather than ‘passive’ which amplify miniscule existing light) I’m certain the effect is less “thermal” and somewhat more the fact that various surfaces reflect IR differently.
In the case of my goggs, which were old Israeli copies of an early American design (from what I’m told) they amplified infrared, but had no built-in source. I made one using some IR LEDs from Radio Shack, and later got a filter to put in a regular flashlight.
It was actually rather interesting looking at things with them- you think your carpets and clothes are clean? Look at 'em under an IR-illuminated NVG. You can see the spots where you’ve dribbled ketchup on your T-shirt, even though you’ve since laundered it a dozen times. You can see outlines of spills on the carpet that have been long since cleaned up, and even places on walls where an area was touched up with a different brand of the same color white paint.
Photographs were interesting- some you could see normally, some, presumably using different paper, appeared to be blank rectangles.
Same with magazines- some of the high-end glossies might have many pages where you could only see squares where the photos and text are, but no details.
Calico cats appear to be a solid color. Some solid-color plants and flowers appeared to have patterns.