More Fun With a Thermal Imaging Camera

How does hot air at 450°C show up on a thermal imaging camera:

It doesn't until you allow it to hit an object (in this case paper)
 See video here:

Comparison of Atmospheric Transmission Germanium Lens response and quoted FLIR camera response
Note that the camera response is in a highly transmissive part of the atmospheric transmissive window - to put the passband in a place where the GHGs radiate would give continual fogging due to the air between object and camera rather than the object desired.

How good is bubble wrap (packing material with 0.5cm air bubbles trapped between plastic)

Single and double layers over hand. The spot temperature has had the emissivity adjusted so don't believe the temperature!
See video here

Using the software's ability to calculate emissivity from the displayed temperature and the known hand temperature (approx 37°C with emissivity 0.92) gives the following results:
1 layer of bubblewrap requires an emissivity of 0.70 to correct the hand temperature to 37°C
2 layers of bubblewrap requires an emissivity of 0.69 to correct the hand temperature to 37°C 
4 layers of bubblewrap requires an emissivity of 0.58 to correct the hand temperature to 37°C
8 layers of bubblewrap requires an emissivity of 0.55 to correct the hand temperature to 37°C

Compare this to 2 layers of cling film (saran wrap/ldpe) here

2 layers of ldpe are equivalent to 4 layers of bubble wrap (8layers of plastic and some air)

So an IR window of 2 layers bubble wrap  (bubbles interspersed) will be better at IR transmission and probably better at conduction prevention.

You need aluminised bubble wrap to prevent hypothermia - need to stop the loss of IR!!!!


  1. What about hot CO2 ? Ah, then I remembered, Your camera doesn't necessary see CO2 IR-bands..

    But If you could reflect IR of hot CO2-jet to paper by some parabolic reflector and measure the paper warming.. ?

  2. Camera response and Atmosperic response curves now added to the post. Focussing IR onto paper would be possible.

  3. To understand what is happening here you have to go to first principles: thermoelectrics.
    This has been my work.

  4. The thermo electric sensors - metal that warms and its resistance changes (a microbolometer) in the cameras I have seen have bandwidth as shown above. CO2 O2 N2 H2O don not radiate in this bandwidth (O3 seems to). There is no visibility of the heat in the air - This is "lucky" since a thermal imaging camera would not work in an air filled room - it would be like looking through fog!
    water vapour is shown to be invisible to the camera: https://youtu.be/6yTErdEg_OE
    thermal image of cloud and cloud free sky https://climateandstuff.blogspot.com/2012/12/sky-temperature-and-thermal-imaging.html
    clouds have grey body spectrum allowing visibility. Open sky c02 o2 n2 etc water vapour is invisible to the camera.
    of interest reflectivity is demonstrated here https://youtu.be/fzzAcxncBMo