Infrared scene simulation

Hi All,

I'm currently trying to find a way to simulate the radiant power distribution for a given scene in the far infrared (about 8-14um wavelength). Using the search option I saw that there already was a discussion on this subject, but I can only find fragments of it - so please forgive me if I ask questions already answered ;).

So my question is: How can I model a blackbody source at about 300°K as radiation source?

I tried using blackbody.cal and and xyz_rgb.cal as I saw in another posting:

echo 300 100 | rcalc -f blackbody.cal -f xyz_rgb.cal -e 'xi=cct_x($1);yi=cct_y($1)' -Yi=$2;Xi=Yi*yi/xi;Zi=Yi*(1-xi-yi)/yi' -e '$1=R ( Xi,Yi,Zi ) ; $2=G ( Xi,Yi,Zi ) ; $3=B ( Xi,Yi,Zi ) '

and it results in

18.3632205 143.92786 0

So I modeled the blackbody as polygon light source with this RGB values and it's real physical extent.

First of all I must admit I don't understand the YL lightning parameter (100 in this case). Shouldn't this already be clear by giving the temperature of the blackbody?

And are these values correct for the infrared radiation the blackbody emits at such low temperatures? Or do I still have to define the spectral range I'm interested in somehow?

It would be great if someone has already experience with thie and could give me some tips.

Thenks in advance and best regards

Alex

···

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Hi Alex,

Unless you are concerned about how the surfaces look to a human observer, there's little sense in modeling a 300K blackbody as a color. You are better off treating total radiance, using identical RGB intensities and reflectances throughout, and just considering the energy transfer.

The main problem with Radiance as an IR engine is that it doesn't consider the ambient temperature and radiation of all surfaces -- only light sources and reflections thereof. Some people have fudged this by considering a surfaces absorption and re-radiation as a kind of diffuse reflection, but this is a poor approximation for 300K, which is just above room temperature. It only works when there is one high-temperature surface acting as a heat source.

Bottom line: I don't think Radiance is well-suited to your problem.

Best,
-Greg

P.S. The cct_x(t) and cct_y(t) functions in blackbody.cal are also not reliable for such low temperatures -- it's meant for visible blackbodies. 300K is in the far infrared.

···

From: Alexander Utz <[email protected]>
Date: May 28, 2009 3:52:14 AM PDT

Hi All,

I'm currently trying to find a way to simulate the radiant power distribution for a given scene in the far infrared (about 8-14um wavelength). Using the search option I saw that there already was a discussion on this subject, but I can only find fragments of it - so please forgive me if I ask questions already answered ;).

So my question is: How can I model a blackbody source at about 300°K as radiation source?

I tried using blackbody.cal and and xyz_rgb.cal as I saw in another posting:

echo 300 100 | rcalc -f blackbody.cal -f xyz_rgb.cal -e 'xi=cct_x($1);yi=cct_y($1)' -Yi=$2;Xi=Yi*yi/xi;Zi=Yi*(1-xi-yi)/yi' -e '$1=R ( Xi,Yi,Zi ) ; $2=G ( Xi,Yi,Zi ) ; $3=B ( Xi,Yi,Zi ) '

and it results in

18.3632205 143.92786 0

So I modeled the blackbody as polygon light source with this RGB values and it's real physical extent.

First of all I must admit I don't understand the YL lightning parameter (100 in this case). Shouldn't this already be clear by giving the temperature of the blackbody?

And are these values correct for the infrared radiation the blackbody emits at such low temperatures? Or do I still have to define the spectral range I'm interested in somehow?

It would be great if someone has already experience with thie and could give me some tips.

Thenks in advance and best regards

Alex

Could you use a mix material of glow and reflective materials to
simulate radiation of other surfaces?

It would still be ignoring convection and conduction though.

-Chris

···

-----Original Message-----

The main problem with Radiance as an IR engine is that it doesn't
consider the ambient temperature and radiation of all surfaces -- only
light sources and reflections thereof.
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You could mix a glow with a reflective material, and others have done so. I don't hold out much hope of useful results at or about room temperature, though. There are just too many things other than radiative transfer going on, as you note.

-Greg

···

From: "Christopher Rush" <[email protected]>
Date: May 29, 2009 10:10:39 AM PDT

Could you use a mix material of glow and reflective materials to
simulate radiation of other surfaces?

It would still be ignoring convection and conduction though.

-Chris

-----Original Message-----

The main problem with Radiance as an IR engine is that it doesn't
consider the ambient temperature and radiation of all surfaces -- only
light sources and reflections thereof.

Hi Greg,

first of all thank you for your answer.

I'm aware that modelling infrared radiation as a visible color doesn't make sense in that way. I just wasn't able do figure out how to create a source with the corresponding energy. In my application there would be on esource - a blackbody - at several degrees above roomtemperatur. I want to know the amount of energy which arrives at a certain area within the scene also regarding the energy emerging from other object in "sight" of the detector area.

I thought it might be possible to model the surfaces of these other objects as radiation sources as well, according to their temperature (which will be about 20°C) and emessivities/reflectances in the far infrared. When searching for a solution I appeared to me that radiance was the most promissing tool - but if you say it's not possible I fear I will have to search on.

Maybe you know a better alternative?

Thanks,
Alex

···

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Sorry, Alex -- it's not really my area of expertise.

Anyone else care to suggest something?

-Greg

···

From: Alexander Utz <[email protected]>
Date: May 29, 2009 10:36:58 AM PDT

Hi Greg,

first of all thank you for your answer.

I'm aware that modelling infrared radiation as a visible color doesn't make sense in that way. I just wasn't able do figure out how to create a source with the corresponding energy. In my application there would be on esource - a blackbody - at several degrees above roomtemperatur. I want to know the amount of energy which arrives at a certain area within the scene also regarding the energy emerging from other object in "sight" of the detector area.

I thought it might be possible to model the surfaces of these other objects as radiation sources as well, according to their temperature (which will be about 20°C) and emessivities/reflectances in the far infrared. When searching for a solution I appeared to me that radiance was the most promissing tool - but if you say it's not possible I fear I will have to search on.

Maybe you know a better alternative?

Thanks,
Alex

Hi Greg,

after I put some more unsuccessfull effort in trying to find an alternative
to Radiance for my infrared-simulation problem I decided to try it with Radiance
and see what comes out. So I hope you don't mind if I bother you with some
stupid questions again.

I calculated the total amount of energy emitted by a 300°K blackbody as
146.305W/(sr m^2). So the material for my source becones

     void light bright
     0
     0
     3 48.77 48.77 48.77

right? Now my Problem is how to create a material mixed from a glow and a
reflective material. I must admit I am not able to figure out how to do this
from the available documentation. I tried the following

     void plastic brown
     0
     0
     5 .2 .1 .1 0 0

     brown glow brown_glow
     0
     0
     4 100 100 100 100

     brown_glow sphere BB
     0
     0
     4 2 1 1.5 .125

just as a test. oconv runs over it without complaints - but when I wan't to
watch the scene using rvu it says:
  rvu: fatal - conflicting material "lbrown" for sphere "BB"

By the way what exactly does the maxrad parameter for the glow stand for (I
don't understand what is meant by shadow testing in this context)? Is it the
maximum distance from the glow which will be illuminated by it's radiation?

I also checked the documentation on mixtures but again do not know how I could
use these to solve my problem.

So it would be really great if you could help me out or tell me how others
solved this as you said!

Thanks and Best Regards

Alex

···

---------------------------------------------------------------------

Sorry, Alex -- it's not really my area of expertise.

Anyone else care to suggest something?

-Greg

From: Alexander Utz <AlexanderUtz at web.de>
Date: May 29, 2009 10:36:58 AM PDT

Hi Greg,

first of all thank you for your answer.

I'm aware that modelling infrared radiation as a visible color
doesn't make sense in that way. I just wasn't able do figure out
how to create a source with the corresponding energy. In my
application there would be on esource - a blackbody - at several
degrees above roomtemperatur. I want to know the amount of energy
which arrives at a certain area within the scene also regarding the
energy emerging from other object in "sight" of the detector area.

I thought it might be possible to model the surfaces of these other
objects as radiation sources as well, according to their
temperature (which will be about 20°C) and emessivities/
reflectances in the far infrared. When searching for a solution I
appeared to me that radiance was the most promissing tool - but if
you say it's not possible I fear I will have to search on.

Maybe you know a better alternative?

Thanks,
Alex

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Hi Axel,

Thanks for explaining your exact problem. The documentation for Radiance is scattered and frequently application-specific. Did you browse the "Seminars and Course Notes" section of:

  http://radsite.lbl.gov/radiance/refer/

Francesco Anselmo's Radiance wiki is also useful:

  http://www.bozzograo.net/radiancewiki/doku.php

Check out Axel Jacob's tutorials at:

  http://luminance.londonmet.ac.uk/learnix/docs.shtml

As for describing a mixture, you need to use the "mixfunc" type. Correcting what you gave in your e-mail:

I calculated the total amount of energy emitted by a 300°K blackbody as
146.305W/(sr m^2). So the material for my source becones

     void light bright
     0
     3 48.77 48.77 48.77

Don't bother dividing the value up, just give it three times:

      void light bright
      0
      3 146.305 146.305 146.305

     void plastic brown
     0
     5 .2 .1 .1 0 0

     brown glow brown_glow
     0
     4 100 100 100 100

     brown_glow sphere BB
     0
     4 2 1 1.5 .125

Should be:

      void plastic brown
      0
      5 .2 .1 .1 0 0

      void glow bit_of_glow
      0
      4 100 100 100 100

  void mixfunc brown_glow
  4 brown bit_of_glow 0.5 .
  0

      brown_glow sphere BB
      0
      4 2 1 1.5 .125

···

--------
Note that I gave half of each, so their actual values will be reduced by 50%. In some cases, you may wish to double the parameters to compensate.

Cheers,
-Greg

From: Alexander Utz <[email protected]>
Date: June 4, 2009 8:12:53 AM PDT

Hi Greg,

what I want to know is the distribution of Infrared Radioation in a Test System
for an infrared camera. So temperature of the objects in the scene is known and
well controlled. I would like to figure out inhomogenities in radiation flux over the
IR detector array due to different system setups and things like that. By the way
the basic IR detectors will reside in a vacuum and their temperature will be controlled
isolated from the rest of the system. So I think convection should not play a role
in that case.

I have to thank you once again - I know this has nothing to do with your expertise
and I can imagine there is stuff you like to do more than answering my ongoing mails ;).
But if you think there is any hope in using Radiance for this issue it would really help
me if you could give me a kick on how to model those self-luminous materials. I will
have to validate the results some day, anyway.

I must say that I find it very hard to figure out much more than the basic scene generation
and rendering mechanisms from the freely available documentation, but I'm not to
experienced with all this stuff, yet.

Thanks,
Alex

Dear Greg,

I wonder if I could ask if it is possible to use Radiance to assess the albedo of an urban setting, e.g. a street gorge, where Radiance can take into account the near infra-red component of the solar spectrum as well as the visible one, please? Perhaps the visible component would have to be assessed first, and then the IR on a second run, after modifying the surface reflectances?

Many thanks

Richard Watkins

Kent School of Architecture : University of Kent : Kent : CT2 7NZ

Richard,

I worked with non-visible wavelengths during my Thesis. When I asked if it
was possible, people in here told me "Math is Math, as long as you include
the correct reflectances, it will work".

If you do not go to the FIR; where every "warm" surface is actually an
emitter and absorber, I would say it will work.

···

2014-07-22 7:39 GMT-04:00 Richard Watkins <[email protected]>:

Dear Greg,

I wonder if I could ask if it is possible to use Radiance to assess the
albedo of an urban setting, e.g. a street gorge, where Radiance can take
into account the near infra-red component of the solar spectrum as well as
the visible one, please? Perhaps the visible component would have to be
assessed first, and then the IR on a second run, after modifying the
surface reflectances?

Many thanks

Richard Watkins

Kent School of Architecture : University of Kent : Kent : CT2 7NZ

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