[GRLUG] OFF TOPIC - Speaking of Infrared...
Michael Mol
mikemol at gmail.com
Thu Jan 28 22:04:33 EST 2010
Erp. Yeah, ~300mm. I was off by a factor of 1000.
Meanwhile, for people trying to do the math in their heads:
http://www.futilitycloset.com/2010/01/28/c-story/
Once you've figured that out in seconds, figure it out in years, and
compare long-scale to short-scale.
On 1/28/2010 9:51 PM, Bob Kline wrote:
> Yup. Light is a radio wave. The issue
> is whether one can form images, or
> otherwise manipulate the radiation. e.g.,
> 1THz is about 0.03 cm, which is probably
> in the microwave range, but it can be
> imaged. And it can go through many
> things. And since 0.03 cm is much
> smaller than everyday objects, it could
> spot a wiring error in a wall. Or people
> doing all kinds of things in their houses.
>
> But you won't get a unit from Cyberguys.
> What you can "see" depends on technology,
> which always changes, and what you can
> spend.
>
> //endjob -- IBM 360 JCL.
>
> -- Bob
>
>
> On Thu, Jan 28, 2010 at 9:31 PM, Michael Mol <mikemol at gmail.com
> <mailto:mikemol at gmail.com>> wrote:
>
> 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
> <mailto: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
> <mailto: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>
> >> > <mailto: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>
> >> > <mailto: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>
> >> > <mailto: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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>
> --
> :wq
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