Re: [Phys-l] atmospheric transmission

[Brian Whatcott <betwys1@sbcglobal.net>]

At 12:10 PM 11/20/2008, Kyle Forinash, you wrote:
> hi
>
> I want to make my own graphs of atmospheric transmission
> ...I have found data out to 4 micrometers ...but
> not ...for higher wavelengths out to 30 or 40 micron (the full
> earth's blackbody range)....
> Does anyone have any idea where the raw data for these graphs can be found?
>
> kyle


This looked like an interesting question. An experimental question.
The graphs for atmospheric absorption of Sunlight seem to be a
composition of the absorption due to various species: water, CO2, O2
Methane etc., etc.   The individual pieces are evidently open to
evaluation with an IR spectrometer,  but the atmospheric medium
introduces several new parameters: temperature, pressure, dissociation,
composition, for which direct measurement seems to be appropriate.

One could, I suppose come by a standard spectrum for Sunlight
outside the atmosphere - say from Space Lab. That could be a basis
for comparison  with its sea level profile.  Thoughts proceed
to differential measures naturally enough: but there is no
 vacuum column between Sun and Earth to form a basis for
direct comparison.
 Alternatively, a vertical spectrum could be compared with
a slant  profile to  provide the differencing that one would
prefer.
But that would put some parameters into the influence of
 uncontroled variables of atmospheric time and space, pressure
 and temperature, somewhat defeating the differential
method.

A second area of experimental interest would be the choice of
IR sensor. The choice seems to be limited to varieties of
bolometers - of thermopiles, probably with potassium
 bromide windows for examining wavelengths as long as 40 um
Here's a sample thermopile - not necessarily the one to choose
 these days.
http://www.roithner-laser.com/All_Datasheets/Thermopile/TP336x.pdf

For a low-cost beginning, it is true that there are thermopile
sensor chips available now for a unit cost of $17.
Engineer enthusiasts are using orthogonal axes of these
 as  prime stabilizing inputs to autopilots for autonomous
airplane models, I see.

For reasonable sensitivity, there would be a strong case for
deep cooling refrigerants at the sensor



Brian Whatcott    Altus OK    Eureka!