| From: | Adam Getchell <acgetchell@*******.EDU> |
|---|---|
| Subject: | Re: thermographic vision-question |
| Date: | Wed, 3 Feb 1999 09:34:34 -0800 |
>micrometers in wavelength (with 1 micrometer being equal to 1E-6 meter, or
>one-millionth of a meter). (This according to US Army Field Manual 3-50.)
>Thermographic vision, as described in SR, exists in the far-infrared spectrum
>between 14 and 30 micrometers. It's at these wavelengths that the blackbody
>radiation at low temperature ranges (0-100 C or thereabouts) are the greatest.
>At shorter IR wavelengths (less than 14 micrometers) the amplitude for this
>temperature range is too small to be detected.
I did this calculation awhile back the last time the thermographics thread
came up: using Wien's displacement law for a temperature of 300 K (28 C)
the peak wavelength is 9.66 microns.
The peak wavelength for 0C is 10.06 microns, while the peak wavelength for
100C is 7.77 microns. Note that these are maxima for a Maxwell-Boltzman
distribution (which looks somewhat like a skewed, asymmetric normal
distribution with a sharp rise and logarithmic "tail").
Next, atmospheric absorbsion of 2.5 microns and 25 microns is almost
minimal (ie transmissivity approaches 99%), so these wavelengths are of
interest for long range imaging. Yes, transmissivity for visible light (300
- 760 nanometers or so) is also quite high in our atmosphere.
Finally, the sun's surface mean temperature is ~ 6000 K; a blackbody
radiating at that temperature would show maximum emission at 480
nanometers. Our eyes are most sensitive to 555 nm, which is close to the
sun's maximum light output.
>-- Jon
--Adam
acgetchell@*******.edu
"Invincibility is in oneself, vulnerability in the opponent." --Sun Tzu
