John,

 I' m sorry I do not know of any public domain software for mapping energy drop through absorbing gasses. If the absorbing gas is relatively homogeneous then I suggest obtaining a black body calibration source and place it approximately in the same location and set to approximately the same temperature as the target. Then viewing the black body source set to a known temperature you can make adjustments to your IR camera. This is relatively easy with high end cameras that have adjustments for transmissivity. Simply adjust the correction factor until the camera reads the same temperature as the black body.

 If you only have adjustments for relative humidity and distance to object you could possibly use these in combination until you arrive at the set temperature of the black body. (You may have set the relative humidity to 100% and dial in many hundreds of meters before the temperature read out of the IR camera matches the black body.) What you are in essence doing is saying that very humid air at very long distances has the same attenuation as a more dense and absorbing environment has at a shorter distance.

Please be very careful where there is high particulate percentage in the air. I would monitor air temperatures and convective currents closely as these factors may have a significant effect on densities (and thus on transmissivity) in regionalized areas.

If you do attempt to try this method it is important to remember that thecorrection factor will only apply to the particular situation that existed for the test. Different densities and temperatures of the absorbing gasses and particulate matter must be evaluated on a case by case situation.

 Hope this will be of help.

 Rob

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Rob Spring, P.E.
Snell Infrared

Flir has a neat publication on seeing through “less than perfect air” it is “Seeing through fog and rain with a thermal imaging camera, Metrological effects of Fog & Rain upon IR Camera Performance” it can be found at http://www.eurasia.flir.com/uploadedFiles/CVS/Appl_story/Technical_Notes/ENG_01_FOG.pdf

 

Another fascinating publication (at least for those of us that REALLY want an IR camera in our car for seeing at night and through fog) is “Advanced Image Sensing for Traffic Surveillance and Detection”.

 

Another source is the classic “Infrared Handbook” by Wolfe and Zissis.  An awesome resource that generally gives me a migraine.

 

--
John C. Lafeber, P.E.
NCII - North Coast Industrial Imaging
4165 Stein Road
Ann Arbor, MI 48105

734-904-0870
LeanIR@gmail.com

 

 

John is right on about the IR handbook. It is filled with charts and graphs of some very usefull and yet some very arcane information. It is horribly organized, with an almost useless index. Some sections read as if the intent of the writer was to use as many difficult and multisyllable words as possible. Yet it has information that to the best of my knowledge is available no where else. It is now out of print and is commanding some crazy pricing on Amazon used books. It was until recently part of the body of knowledge for the ASNT LIII exam. The only way this book has become useful to me is that I have read the thing in almost it's entirity and periodically (once or twice a year) a question comes up and I know I saw something in the IR handbook. If your not willing to get familar with this book save your money.

 Nondestructive Testing Handbook,  Infrared and Thermal Testing , Published by ASNT is now considered the new "bible". It is better organized and yet I find it also difficult to extract information quickly. It has many authors and does not read with a uniform voice. It also is rather redundant as many authors repeat basic topics (not bad for the new thermographer). It has the advantage of being more up to date, and covers thermal NDT in more depth.

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Rob Spring, P.E.
Snell Infrared

Thank you John and Rob.

WRT the 'Bibles', I had a similar problem in a field that I work in (not IR).  In the end, we acquired the licence to print the older, partly obsolete books ourselves under separate title and are in the process of updating and producing our own resource.  I'm sure Snell has already considered this route.   Given how much knowledge you gents have, it would be great to capture it all before you retire and finally find relief from all these questions ;)

Thanks again

-John

Rob,

 

Your ammended formula is acceptable assuming the effects of reflected background radiation and atmospheric effects can be neglected. This is often the case with the atmosphere, but seldom the case with reflected radiation. As you know, the more you lower the emissivity, the more this comes into play, so the more they correct for emissivity, the bigger the potential for error is with the formula. I personally think that it is a little irresponsible to suggest that formula like this can be used, particularly on messageboards. Formula like this should ONLY be discussed in a classroom enviroment, where their practical use can be explored (my opinion). Using formula like this is very often beyond the capiabilities of the people that are going to try to use them, normally people that are capiable of using them are well able to derive the formula for themselves. I would suggest that the majority of people use this for guidance only, and do not over rely on the calculated results.

---

Bob Berry
BINDT, IRT Level 3 EL, Level 3 CV (ISO 18436)
Thermal Vision
8 Old Fair Green
Dunboyne
Co Meath
Ireland
bob@thermalvision.ie
www.thermalvision.ie

 Bob,

I agree with your concern about people using formulae who do not have an indepth knowledge of all of the factors. If you read through the entire post where I presented the formula you will notice the caveat I included.

"We always hesitate suggesting the use of formulas by people who may not understand the relationships between all the variables. As has been discussed by others above, the effect of background increases as the emissivity decreases, meaning that the lower the emissivity the more certain you must be of the accuracy of the background signal."

If you have a copy of Experimental Methods for Engineers you will notice that the author does not give any warnings about background or atmospheric effects. Because this reference is part of the ASNT body of knowledge and is readily available to many people I felt it best to state the formula, but add the warnings. We are constantly bombarded by individuals who want a "formula" to; estimate energy savings, calculate the temperature when the wind stops, predict the temperature inside an enclosure given only the surface temperature, etc. etc. In all cases we state emphatically that the variables are most always too great to overcome in field situations. I have on two occaisons used the above stated formula when desparate thermographers needed a temperature where the emissivity variance was not great. In each case we discussed all variables and the reported temperatures we posted with appropriate caveats. 

I do want to also bring to the discussion that this formula does nor more than what any thermographer can do in software when they re-adjust the emissivity or background on a saved image. I have yet to seen warnings by the manufacturers telling thermographers "never adjust emissivity or background unless you are qualified and understand the relationship between these variables."

Thanks for emphasizing this important point again, it has broadened the discussion and that is the value of message boards like IR Talk.com.

Rob

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Rob Spring, P.E.
Snell Infrared

Rob,

I did notice you're caveat, I just felt it necessary to emphasise the problems with this. I agree that camera software does not issue caveats, and sometimes makes things seem more simple than they are. I know some cameras do issue warnings about temperature measurement when the emissivity is set low, but this only happens when it is ridiculously low.

 

 

www.thermalvision.ie

 

---

Bob Berry
BINDT, IRT Level 3 EL, Level 3 CV (ISO 18436)
Thermal Vision
8 Old Fair Green
Dunboyne
Co Meath
Ireland
bob@thermalvision.ie
www.thermalvision.ie