Flower FLIR

[Cadmium]

Small daisy flowers, and dandelion seed head shot with FLIR.

I chose these subjects that were located in the shade to avoid reflected sunlight warmth which can complicate and confuse examination.

 

 

 

 

[otoien]

Interesting, so what do you think is causing the hotter flower heads?

[Cadmium]

Insulation. Maybe. The daisy flowers are about the same height as the grass and other foliage, but has more layered structure.

The seed head is higher above the surrounding foliage, but it is somewhat sheltered on the inside, so both of these structures may be more insulated from the air and wind, and retain heat longer.

Just a guess.

[otoien]

So retaining heat from previous sun exposure/temperature change/ongoing background IR radiation? (Metabolism likely too low to produce enough heat).

[Andy Perrin]

My thinking is that it is simply darker in visible light so it absorbs more sunshine and gets warmer, even after the sun has moved on.

[Cadmium]

Especially those daisy flowers were in an area that was in the shade all day, or most of the day, and not in the sunshine at any time recent to the photo.

The seed head I am not sure how long it had been in the shade.

I am not sure the heat is something that is from being in the sun and retaining heat from that, it might have to do also with air/wind-chill ?

Just not sure that in either situation that the temperature has much to do with direct sun exposure. That would be my first guess, but given the locations, I have to wonder further.

I don't suspect the heat is coming from the plant/flower.

 

Also, you might notice a few smaller blue and magenta flower in the background (seed head shot).

Also I shot some forget me not flowers (Myosotis), same size and structure as the magenta flowers, and they didn't seem to have any difference in heat compared to surroundings.

Those smaller background flowers have no heat difference from the surrounding glass and leaves, but those have a simpler less dense structure.

[OlDoinyo]

Does this imaging device actually record peak wavelength or intensity? If only the latter, it might be perilous to draw conclusions about exact temperature of any portion of the subject: thermodynamics tells us that if the subject has lower reflectivity in the wavelength range in question (i.e. it is "black,") it will radiate more intensely than an object of the same temperature with high reflectivity ("white,") even though the black-body spectrum may be identical. If the color-coding of the image is merely intensity, it follows that the image is not really a temperature map.

[Andy Perrin]

OlDoinyo, definitely you can read temperature off of a properly calibrated thermometric image. I think what you are getting at in a very roundabout way is that the emissivity (ratio of the actual light power emitted to the power emitted if it were a perfect black body) of a given surface can vary a bit. This is true, but it is around 0.9-0.95 for most non-metallic solids, so it is responsible for just a few percent variation in most cases, and for the most part one can read temperatures quite accurately without it causing much error. However, it is possible that this is enough to produce the slight difference observed above.

 

By the way, the color of a surface in visible light has very little to do with the average emissivity of the surface. To give an extreme example, freshly fallen snow (emissivity = 0.97) is a pretty good blackbody despite being white.

[OlDoinyo]

I was not referring to the visible reflective properties, but rather those in the wavelength range in question--that is why "black" and "white" are in quotes.

 

Fun fact: Snow is "black" in the ambient thermal band, which is why it cools so efficiently at night under clear skies, and why it causes nights to be much cooler than if it is absent (it is also an efficient conductive insulator and blocker of heat transfer from below, which helps the snow surface cool rapidly.) Water molecules absorb a lot of mid- and far-IR due to vibrational and rotational modes.

 

I gather what you are saying is that most other surfaces are similarly "black" in this wavelength range. I would guess that some surfaces, such as table salt, might not be.

[Andy Perrin]

Fun fact: Snow is "black" in the ambient thermal band,

That is what I just told you. It has an emissivity of 0.97. Your fun fact is the same as my fun fact.

 

I gather what you are saying is that most other surfaces are similarly "black" in this wavelength range. I would guess that some surfaces, such as table salt, might not be.[

Yeah, table salt is a rare exception to the rule. It is used for lenses sometimes. But that isn't the situation with flower heads, which are probably in the 0.9-something range like most other electrical insulators.

[Cadmium]

I think I will let you two work out the details. I wasn't inferring anything, I was just asked what I thought, just a guess, I have no conclusion.

 

As far as these shots, just to explain the thermal image, the center of the pic has a rectangle, hard to see, but you might see little white corners defining the rectangular area,

the cross is the hottest spot within that rectangle, which is the temp noted at the upper left.

The min/max temps shown on the bar graph at the right side, may be for the whole frame, not sure.

There are different ways to set all that up, or not at all, but it isn't that meaningful to me in these shots really, just that the flower and seed head are warmer than the rest of the shot.

Make of it what you will.