Water Vapour and Thermal imaging

More stuff about thermal imaging.

Looking at the sensitivity spectrum for a FLIR thermal camera much of the CO2 and H2O emission spectra are included but it is not a black body spectrum as the camera expects.

So does this mean that CO2 and water vapour should be less visible to the camera?

For the camera this is important since taking a photo through air which is emitting photons visible to its sensor would make its use limited – you would see the air not the object behind the air.

So a simple test using water vapour was done to see if this was the case

Some videos of a hot plate with 2 wells filled with water, The water is boiling but no hot vapour visible (vapour bubbles show approximately the expected temperature but the only vapour visible is less than 40°C.

If you now place a sheet of paper in the vapour the actual temperature of the vapour as it hits the paper can be seen (greater than 70°C)

Steam shows up at 28C

Shows paper being heated to 75.5C by steam invisible in gap between boiling water amd paper.

Heated plate showing 2 wells with boiling water

These videos show differen views of the hotplate - steam - paper system.

  

Steam visible + paper

Top view of plate, boiling water and paper

side view of plate boiling water and paper

Above videos seem to have problems  so a youtube version:

http://www.youtube.com/watch?feature=player_embedded&v=l3t9XeTIA1w

Conclusion: H2O vapour behaves as expected - despite the temperature being near boiling (100C) it does not appear so to the camera.