How come wind doesn't mess up thermal imaging?

If you are sensing the heat coming off of an object--the heat EMANATING off of an object in a 360 degree arc---How come wind doesn't distort the image (or cool the air) coming off of the object?

And for that matter why is the air not all the same temperature around the thermal sensor? If you compare it trying to sense a heat source in a body of water: All the water far away from the heat source is the same temperature. Can you imagine being in a lake and using a sensor to see 100 feet through the lakewater to see a hand warmer in the bottom? It makes no sense! Help!

Midwave uncooled bolometers only measure the surface temperature of the object, not the temperature inside or outside the object.

Same reason wind does not distort what you can see.  Your eye ball detects radiation within a certain frequency range that travels at the speed of light from the source to your eye. Unless something between the source and detector (eye or thermal device) blocks/absorbs, refracts, or reflects the radiation.  If the normal atmosphere does not block/absorb, refract or reflect thermal radiation,  it can not acquire the ability to do so because it is moving relative to source or detector.

If the wind force had an affect on the surface between source and detector that raised up material  that blocked/absorbed, refracted or reflected thermal radiation, such as a "sand storm" then yes, out put from the detector will be degraded.

I guess I thought heat acted like convection--as in water--it heated the atmosphere around it and radiated from molecule to molecule as they vibrated via heat. I guess like sound waves travel. Wind definitely affects sound.

Someone please correct me if I'm wrong...

OP, I think the confusion here is that your thermal imager isn't literally seeing heat; it's detecting a wavelength of the EM spectrum where the emissivity is largely determined by the temperature of the material. So wind doesn't affect it for the same reason wind doesn't blow away the green light you see reflected off the trees.

I contribute this to either clarify or add mystery to the discussion.

Farts are visible on thermal.   A gas at a different temperature, but still transparent in visible light, is visible in thermal.

Yet it still operates as a transparent medium.    Interesting.

Pretty much this.

The sensor is picking up thermal radiation from objects emitting it. The air is emitting some thermal radiation, but it’s just a small amount of noise in most cases. You can detect cold and hot air if there is a good amount of contrast though, like the farts above or a poorly sealed window.

thermal energy is either emissive or reflective. all objects emit radiation waves that can be detected and presented to the thermal imager. well, that is all things with a temp above 0 deg kelvin. in addition, those radiation waves can bounce off of other objects. this is why you see great reflections in things like aluminum. what makes it interesting for the detector is that it can represent a temp based upon what it sees, but if the thermal radiation is a combination of direct (emissive) and indirect (reflected) then you will "measure" and see a different image.

so, the fart is heated gas radiating energy, and the thermal sees it. the person standing next to a stainless shiny wall, you will see both the person and the reflected person.

figure this out. take a thermal camera and look a the water front. see all the waves? can you see the water? why? isn't the water all the same temp? if it is the same temp, then why do you see such a clear image?

thermal is cool but it only sees and presents the results of what is sent as a wave.

Air is transparent to the IR light that a thermal imager sees.

Objects emmit that same IR light in proportion to their temperature.

Air has to be really damn hot, like plasma hot, before it will emit enough of that IR light for a thermal imager to "see" it. Even then it's kind of iffy.

You're probably seeing particulate matter in the fart that is thermally emitting, not actual gas.

Gross, right?

Alternatively, perhaps methane isn't transparent in the relevant wavelengths like nitrogen/oxygen is. As it mixes with the air this attribute would degrade and be lost.

the trermal radiation travels at the same speed as light so it will not have time to be blown off course by the wind etc.

OK I was misunderstanding how it works. So bizarre and cool...

That's so fake it's not even funny.

SkyPup to the courtesy phone please

Agreed.  Complete BS.  Even a cooled midwave camera can't see a fart.  LWIR systems are usually sensitive to temp differences down to 20-30 miliKelvin, which is roughly .02-.03 degrees C.  As M855 indicated, air is transparent to thermal, unless there is a significant amount of moisture content present.  LWIR can only see a milimeter or two through water.  No possible way to see anything hot at the bottom of a pool/puddle.  Flir's gas finder cameras use notch filters and are tuned for specific EM bands within the IR spectrum.

Hot gas/air can be observed in thermal, but it has to be extremely hot.  Have a look at Skypup's images in this thread...https://www.ar15.com/forums/Armory/Why-do-metal-roofs-look-strange-when-viewed-with-thermal-/18-489315/.  Heated air can be seen wafting from the torch.

Also, here's an image of a lighter from a Boson 640

Here is a thermal video of me filling up a Dewar Flask full of Recombinant Viruses with Liquid Nitrogen at -273 Farenheit, you can barely see the nitrogen gas pouring out the mouth.....

https://www.youtube.com/watch?v=iAg82XHVN-w&feature=youtu.be

Our atmosphere is composed of 78% nitrogen gas.....

Think of thermal as just another color we can't see. Thermal imagers see that color.

Objects that are relatively warm or hot will emit wavelengths in that band, just as something really hot will emit wavelengths in the visible spectrum. You can heat up a large ball to 2000 degrees so it glows brightly, but you can't see what's in the middle, because light can't get out of a solid ball - you can only see the light emitted by the surface, or perhaps beneath it if the material is transparent to that color. Just like our sun is super-hot in the inside - 27 million degrees. That kind of heat would kill us through UV radiation if we saw it, but we can't because that radiation is absorbed by the sun again long before it ever reaches the surface. On the surface it's just around 5500 degrees - so that is the color of the sun we see.

Some things like glass act like mirrors. You don't see the glass like you don't see a mirror. You see what's reflected in it. Thermal colors are reflected by glass, so we can't measure the temperature of glass with a thermal meter. Likewise some metals just reflect light, so you can get a better heat measurement from them by putting some tape on them.

Likewise, a polished metal pot might be red hot but we tend to see reflected light in it, while a dirty or rough metal pot heated to the same temperature on the stove might appear to be glowing.

How much this "glow" appears to how much a perfect radiator glows is called emissivity. Shiny stuff has low emissivity. You can't measure the heat of a shiny aluminium pot, but you can measure the heat of an anodised aluminium pot with a thermal sensor.

Many materials reflect some thermal light to some extent. A car's hot exhaust may appear to be heating the ground to a thermal imager, but when the car moves, there is no real heat absorption from the ground - it's just reflecting some of that back at us.

Air does distort thermal colors just like it distorts visible light colors. It can bend thermal light too, but air is mostly transparent to thermal light. You can't see very hot air just like you can't see warm air. However some gases do absorb different colors of light and this is why some gases can be detected by thermal - it's just how a yellowish gas might appear yellow because it absorbs blue light, but it only appears that way because there is white light behind it and around it. If you used blue filters, it would be much easier to see. If you used red filters, you wouldn't see it at all. Same with thermal light.

People who use thermal sensors in their work need to learn how to avoid misreading temperatures because of all of these factors - and sometimes they still do make mistakes.

But generally, thermal colors are just like visible colors - only they have really long wavelengths in comparison - more than an order of magnitude longer.

David.

Yeah you can't see farts on thermal.



Crappy Thermal image (first generate Seek Thermal plugged into my Samsung S6) but this is my Milwaukee heat gun running on high, point up.  The nozzle is actually at ~1000 deg F (entering the visible spectrum) but the sensor maxes out at 626 deg F.  There is almost no distortion to the image above the running heat gun.  You can still see the slightly warmer power cord in the back ground that is heating up due to the current draw from the heat gun.

Now that's how thermal should look! Very impressed by the crisp clear image

I agree I think the skeetir has one of the best images out. At its price point though, it should.

You guys are helping me tons--thanks!

I have noticed while checking things out at night that large insects like junebugs flying around are showing very 'hot' -- Is this because the little guys are putting off heat while flying, or because they are 'reflective'?