Message Board Thread - "IR Reflection"

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IR Reflection IR Newbie 5/6/2009
Question: Why when I take hmm, let say, glass filled with hot water and put it on the table. i look at the IR image and i see the reflection of the glass on the table. also when i measure the temp on the table with the 'spot' feature on my camera i could see false temp result, similar to the real temp. of the glass. could someone explain this phenomena?

thank you in advance.
IR Newbie
P.S, i'll try to attach image later.
 
Re:IR Reflection Bob Berry 5/6/2009
Yes, there are reflections in infrared. The table you are putting the glass on is a mirror reflector in infrared. This is often more of a problem in infrared than in visual. To be fair, in order to explain this fully requires time, and this is only one of the problems you will come across when working in infrared. I strongly recommend taking a Level 1 course, where this and other difficulties that you will come across will be explained.
 
IR Reflection IR Newbie 5/7/2009
Dear Bob, thank you for replying so quickly.
I've done ITC Level 1 course and i'm still not sure i fully understand this phenomenon. I tried to search for more than a superficial explanation i recieved on the course.
BTW, I'm using FLIR SC640.

It will be very helpful if you could send me some information helping me understand the above.
Thank you.
 
Re:IR Reflection Bob Berry 5/7/2009
The camera sees all the radiated energy leaving the surface of an object. This includes the energy from the object itself, reflected energy and in some cases transmitted energy. In the case of a blackbody, you will not have any transmitted energy, or any reflected energy. Realbodies, like your table, will have an element of reflections. If your table had an emissivity around 0.95, this means it would have a reflectivity of 0.05, so it would reflect some energy from the glass. If the table was a diffuse reflector, the reflected energy would be scattered and most likely you would not really see the reflection so well. Your table is a mirror reflector, so you can see the reflection very well.

Bottom line, you need to learn to separate how a material looks visually and how it behaves in infrared, sometimes this will be very different.

I am surprised you don’t understand this after completing a Level 1.

http://en.wikipedia.org/wiki/Reflectivity
http://en.wikipedia.org/wiki/Mirror
 


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