Sean Kelly
Free Thinker
offline
Registered: Jan 2003
Local time: 08:31 AM
Location: Silicon Valley
Posts: 4292
|
They use devices that combine radar & infrared into a useful image. Infrared is the same level of light output that you get from your remote control on your television: you can't see it, but it's there. IR viewers transform light in the IR specturm into an image that may be seen on a monitor. As it happens, IR is able to travel through certain materials - the resultant image isn't clear, but you'll see definite "hot spots" where a warm body is. Other technology like radar gets a bit more sophisticated in the way it sends out pulses and listens for echoes returning to determine various properties of the object(s) that the pulses bounced off of. Similar technology is used by traffic enforcement to monitor how fast vehicles are moving by way of measuring the doppler shift in the returned wavelength (the wave striking an object in motion changes in wavelength proportionate to the velocity of the perpendicular point of incident. An object moving away will cause the wavelength to lengthen, towards will cause it to shorten. This measurable effect may be used as a means of motion tracking, but also of echo-location: this is exactly how bats locate in-flight insect prey despite being "blind as a bat". The military (or is it the public technology sector from whom the military purchases?) has, of course, refined these technologies into precision instruments able to deliver sharp imagery based on the sound and heat waves emmanating through a wall.
That's the two-minute version, anyway.
Smile; It confuses people.  |
|
10-10-2003 11:45 PM
