[GRLUG] OFF TOPIC - Speaking of Infrared...

[Michael Mol]

Ah, in that case, I should have directed my response to Ben.  1THz is
actually far, far, deeper than even the far-IR stuff I work with.
1THz has a wavelength of a few hundred micrometers; My stuff doesn't
even get as long as one micrometer.

It borders on radio waves, which is how it gets its greater
penetration capability.

For a quick comparison:

100s of nanometers -- visible spectrum, IR
~300 micrometers -- This terahertz tech.
~3cm -- 10GHz ISM band, not used for much, but in the general vicinity
of satellite TV.
~6cm -- 5GHz ISM band, commonly used in 802.11a and 802.11n.
~12.5cm -- 2.4GHz ISM band, commonly used in bluetooth, 802.11b,
802.11n, most cordless phones, newer R/C car and airplane controllers.
~33cm -- 900MHz ISM band, mostly used for older cordless phones, R/C
cars and airplane controllers.

Below that, you'll find your over-the-air and cable TV channels.

If you're really worried about see-through-walls EM intrusion, you
could conceivably set up a Faraday cage designed to trap the bands
you're worried about.

On Thu, Jan 28, 2010 at 9:13 PM, Bob Kline <bob.kline at gmail.com> wrote:
> Oh, I understand.  The original question
> was what Cyberguys level gadgets could
> do in terms of seeing bad wiring inside a
> wall.
> If cost is no object, one can of course
> do more.  A lot more.
> Devices operating in the 1THz range
> can see people inside their house.
> Through walls.  There were discussions
> about the legal implications of all this
> several years ago.
>     -- Bob
>
> On Thu, Jan 28, 2010 at 9:04 PM, Michael Mol <mikemol at gmail.com> wrote:
>>
>> On 1/28/2010 8:48 PM, Bob Kline wrote:
>> > How cool was the room?
>>
>> Thermostat is normally 72F, but that's in another room. I'm in the room
>> with the servers, which is usually about five higher.
>>
>> >
>> > You seen to have a short sleve
>> > shirt on, but I think I can see the
>> > back of a chair,  walls in the the
>> > background.  Is it a big room?
>>
>> I wear short-sleeves year-round, primarily because of the higher
>> temperatures in the vicinity of my workstation. That was actually taken
>> in Dec of 2007, I think. (The date is off on Flickr, but that's because
>> the source is a BMP, and the timestamp was screwed up due to a few
>> workstation migrations.)
>>
>> Room is about 750 ft^2, or about 6000ft^3.
>>
>> >
>> > Jet gets to the fact that because
>> > you stand out some the room might
>> > be large, and-or cool
>>
>> I don't think you understand how far-IR temperature monitoring works.
>> If you'd like, I can delve into a discussion of microbolometers and
>> measurement adjustments stemming from surface emissivity, ambient
>> temperature and ambient humidity values.
>>
>> There's more at work than just the wavelength of quanta, there's also
>> intensity of emissions, considerations of atmospheric absorption and
>> considerations of ambient temperatures reflecting off of other surfaces.
>>
>> What it boils down to is that in practical conditions, I can (and do,
>> for use cases such as those that that software was written for) measure
>> surface temperatures to within 0.01C.
>>
>> Don't forget I also control the palettization -- the conversion of raw
>> temperature numbers to RGB pixels, which goes towards making differences
>> "stand out."
>>
>> >
>> >      -- Bob
>> >
>> >
>> > On Thu, Jan 28, 2010 at 8:18 PM, Michael Mol <mikemol at gmail.com
>> > <mailto:mikemol at gmail.com>> wrote:
>> >
>> >     On Thu, Jan 28, 2010 at 8:02 PM, Bob Kline <bob.kline at gmail.com
>> >     <mailto:bob.kline at gmail.com>> wrote:
>> >      > On Thu, Jan 28, 2010 at 6:03 PM, Michael Mol <mikemol at gmail.com
>> >     <mailto:mikemol at gmail.com>> wrote:
>> >      >>
>> >      >>
>> >      >> The chief problem with "darkvision" as it applies to passive
>> >     near-IR is
>> >      >> that there is a lot of ambient near-IR radiation that's not
>> >     related to
>> >      >> warm bodies.
>> >      >>
>> >      >> In short, your warm body radiation in the near-IR will be there,
>> > but
>> >      >> largely drowned out by the ambient near-IR radiation.**
>> >      >
>> >      > The peak wavelength for a human body
>> >      > thermal spectrum is 10 microns - in the so
>> >      > called long-wave infrared range.  You shine
>> >      > if you're standing out in the snow,  but the
>> >      > human body is not really very hot.  About
>> >      > the same as your house interior, which is
>> >      > that temperature, by design. So you don't
>> >      > stand out much.
>> >      > See http://en.wikipedia.org/wiki/Infrared
>> >      >     -- Bob
>> >
>> >
>> > http://www.flickr.com/photos/28208534@N07/3681419505/in/set-72157620862996406/
>> >
>> >     I don't?
>> >
>> > What kind of image is this?  i.e., how
>> > is it corrected?
>> >
>> >
>> >
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