Improved IR Image (TGP IR)

[Bushmanni]

This is something I have been wondering. In some previous thread I expressed the idea that IR radiation from sun is reflected from ground but after some more research I was convinced otherwise. Atmosphere filters out pretty much all other frequencies of EM radiation except visible light. All the stuff that has been heated up during day has been done by visible light which then emit IR radiation. Hence the term "green house effect". So all the heat that thermal camera sees is emitted and not reflected unless the source is inside the atmosphere, ie. big bright explosion or something similar. Now I know that clouds will reflect IR from sun but how is that possible then? Or is the only component that filters IR moisture in the air which occurs only at very low altitude, hence no reflected sun IR at ground level but still in the clouds and snowy mountain tops.

[AlphaOneSix]

Water is a very good "absorber" of IR radiation. That is, water in it many forms has an emisiivity rating varying between abour 0.95 to 0.98. Note that "perfect" absorption is a 1.00 emissivity rating. Water, snow, ice, clouds, etc. reflect almost no IR radiation. Rather, they absorb it rather well then radiate it back out.

 

Emissivity scales range from zero to one and vary,

depending on the type of material. A material which

absorbs the total radiant energy striking it has an

emissivity of 1.0 and is known as a black body.

[Migow]

the game need prerender static lighting for ground tree everything static :

for 5h mission the game render each 1 minute texture with lighting for visual light but also flir

we could have good lighting with that system

[Speed]

This is something I have been wondering. In some previous thread I expressed the idea that IR radiation from sun is reflected from ground but after some more research I was convinced otherwise. Atmosphere filters out pretty much all other frequencies of EM radiation except visible light.

 

You are very incorrect, thankfully! The atmosphere has giant, gaping transparent windows through radio and microwave, and has some pretty significant transparent "windows" in the infrared. Then of course, visible starts. These windows are divided into 8-12 microns (LWIR), 3-5 microns (MWIR), and 1-3 microns (SWIR), above which near infrared and visible light begins. The atmosphere starts become opaque again beyond blue.

 

This is a pretty good image that demonstrates transmissivity through the atmosphere:

 

 

Now a significant portion of solar IR radiation does in fact get blocked, even in the transparent windows, because the IR windows are not perfectly transparent. However, according to a graphical integration of the curve on page 5 of this paper: http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA392905

 

then about 14 Watts/m^2 of radiation in the MWIR window reaches the earth's surface from the sun. This is, incidentally, 0.1% of the total solar irradiance at sea level. According to my calculations a surface with an albedo of 1 exhibiting perfect Lambertian-type reflectance, held perpendicular to the sun, would appear to be about about 60 degrees C when imaged with a MWIR imager.

 

So solar illumination is very important to take into consideration.

Edited July 15, 2011 by Speed

[Speed]

Water is a very good "absorber" of IR radiation. That is, water in it many forms has an emisiivity rating varying between abour 0.95 to 0.98. Note that "perfect" absorption is a 1.00 emissivity rating. Water, snow, ice, clouds, etc. reflect almost no IR radiation. Rather, they absorb it rather well then radiate it back out.

 

 

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Thanks, I tried to google information about snow and I couldn't find any.

 

That said... I clearly remember having seen clouds being quite reflective through a MWIR imager... so are you sure this is always applicable? I'll do some more searches to try to solve the question...

 

OK, here's the first hit I found, and it backs me up that clouds are reflective:

http://wstiac.alionscience.com/wstiac/iacdocs.do?GC-081001-10

 

What's interesting is that they are talking about specular reflection off of clouds.

 

Gonna look for more.

Edited July 15, 2011 by Speed

[Speed]

Ok... page 14, figure 3:

http://modis-atmos.gsfc.nasa.gov/_docs/atbd_mod05.pdf

 

If I'm reading correctly, then the average albedo from all viewing directions of some clouds (small cloud droplets) in MWIR wavelengths can be upwards of 0.4! It seems that as droplet size gets much larger than the wavelength, then absorption skyrockets... which makes sense at least.

 

I wish I knew what the effective temperature of a blue-sky background was... but I'm tired of doing literature searches :(

Edited July 15, 2011 by Speed

[AlphaOneSix]

Yeah I got the opportunity to go flying today and test it out. I should know more about this since I just had a week-long FLIR class two weeks ago. So much for my brain's absorption rate!

[Speed]

Yeah I got the opportunity to go flying today and test it out. I should know more about this since I just had a week-long FLIR class two weeks ago. So much for my brain's absorption rate!

 

Well, how did they look? You get to look at any cumulus? Did they look "white" with white hot, or dark? or grey?

[SmokeyTheLung]

Here's a slightly irrelevant vid showcasing two different generations of FLIR systems (on an Apache).

Gives some good insight into how different FLIR can look depending on the sensor:thumbup:

 

http://www.youtube.com/watch?v=zRcbTtZpoEI&feature=related

[Frostiken]

Here's a slightly irrelevant vid showcasing two different generations of FLIR systems (on an Apache).

Gives some good insight into how different FLIR can look depending on the sensor:thumbup:

 

http://www.youtube.com/watch?v=zRcbTtZpoEI&feature=related

 

Honestly except for image fidelity it looks like they were using two totally different level / gain settings... low level and aggressive gain on the '1st gen' and much higher level on the '2nd gen'.

[Frostiken]

Well, how did they look? You get to look at any cumulus? Did they look "white" with white hot, or dark? or grey?

 

I recall seeing clouds as both, actually - thinner clouds or the edges were 'hot', while they got darker towards the center... less IR, makes sense.

[SmokeyTheLung]

Clouds as seen through a FLIR system @ 0:27

http://www.youtube.com/user/bath831surf400#p/u/7/ohxwoHaCJsE

 

...Also slightly irrelevant but cool none the less

Edited July 15, 2011 by SmokeyTheLung

[Speed]

Clouds as seen through a FLIR system @ 0:27

http://www.youtube.com/user/bath831surf400#p/u/7/ohxwoHaCJsE

 

...Also slightly irrelevant but cool none the less

 

Since that's a PNVS test/comparison, then it would have probably been filmed at night, making it irrelevant to the question over the apparent IR temperature of clouds under direct illumination by sunlight.

[Speed]

Honestly except for image fidelity it looks like they were using two totally different level / gain settings... low level and aggressive gain on the '1st gen' and much higher level on the '2nd gen'.

 

Odd, because the definition of IR systems I learned was scanning = 2nd gen, staring = 3rd gen... or at least something to that effect. And I'm pretty sure I remember the PNVS of the AH-64A being held up (metaphorically :)) as an example of a 2nd gen scanning system. But maybe paulrkii can tell us more specifically... someone out there on these forums has to know for sure.

 

Edit: wtf... maybe my memory is going... but yea... looks like 2nd generation can be staring too. Just googled it.

Edited July 15, 2011 by Speed

[SmokeyTheLung]

Since that's a PNVS test/comparison, then it would have probably been filmed at night, making it irrelevant to the question over the apparent IR temperature of clouds under direct illumination by sunlight.

 

Right slightly irrelevant, like I said...

 

Honestly except for image fidelity it looks like they were using two totally different level / gain settings... low level and aggressive gain on the '1st gen' and much higher level on the '2nd gen'.

 

According to the pilots, they had the FLIRs tuned "as good as they get" (see second vid). From what I can tell the point of the flight(s) was to test the two systems head to head.

 

What I thought was interesting, was how different the thermal image of the trees appear between the two systems

[Bushmanni]

The easiest way to determine how big factor reflected IR energy is vs. emitted one in real life would be to look at shadows of moving objects. Is it possible to see shadows of cars and people during sunny day in thermal camera? I would suspect there's some kind of shadow but how dark it is?

[Speed]

The easiest way to determine how big factor reflected IR energy is vs. emitted one in real life would be to look at shadows of moving objects. Is it possible to see shadows of cars and people during sunny day in thermal camera? I would suspect there's some kind of shadow but how dark it is?

 

Well, the albedo of most everything on the earth's surface tends to be pretty low... low enough that reflected IR solar radiation is drowned out by emitted solar radiation. So you shouldn't see any shadows caused by reflected energy, since all typical backgrounds appear to be MWIR's equivalent of the color black. You SHOULD be able to see a shadow, however, if there was a surface that had a very high MWIR albedo (non-specular, of course)- in regular guy speak, MWIR's equivalent of the color white- but I donno what such a surface would be.

Edited July 15, 2011 by Speed

[Frostiken]

The easiest way to determine how big factor reflected IR energy is vs. emitted one in real life would be to look at shadows of moving objects. Is it possible to see shadows of cars and people during sunny day in thermal camera? I would suspect there's some kind of shadow but how dark it is?

 

The underside of running vehicles tends to have a huge cushion of "light" on FLIR.

[112th_Rossi]

IR signature isn't always directly linked to heat god damnit

 

Yes it is.

 

Heat is a form of light which operates mostly in the infrared.

[Speed]

Yes it is.

 

Heat is a form of light which operates mostly in the infrared.

 

No, roughly, heat is the difference between the sum of the kinetic energy for each molecule added together, minus the macroscopic kinetic energy, which would be kinetic energy calculated by finding the average value of the velocity of all the particles combined. This is a simplification because molecules in a fluid are also free to rotate and can thus have rotational energy which adds to heat, but anyway, it roughly gets the point across: heat is molecules, or the atoms in a crystal lattice, vibrating, that does not sum up to motion in any particular direction. In other words, heat is the energy of disorganized motion in a system. Anyway, that's my understanding at least, but I did the minimum I needed to do to get the grade I wanted in Thermo and no more. Thermodynamics doesn't really interest me that much.

Edited July 19, 2011 by Speed

[Eddie]

Yes it is.

 

Heat is a form of light which operates mostly in the infrared.

 

No IR is a form of light, heat is a form of energy, IR emissions are but one possible method of energy release by high energy particles. Although related they are not the same.

 

A high temperature of a given object doesn't NESSESARILY mean it's IR signature will be higher than something with a lower temperature.

 

Something doesn't HAVE to be hot to have a large IR signature and vice versa.

[asparagin]

No IR is a form of light, heat is a form of energy,

 

Don't do this to yourself.. I tried to explain that a couple of pages earlier..

 

Thermodynamics doesn't really interest me that much.

 

Who does nowadays? :P

Edited July 19, 2011 by asparagin

[Eddie]

Don't do this to yourself.. I tried to explain that a couple of pages earlier..

 

I know, but you explained at university level. :D I was trying to make it more understandable to a normal human using more school speak. (Yeah I know, just about everything you learn in science at school is wrong). ;)

[Milene]

So are we gonna see proper hot and cold instead of a filter?

[LostOblivion]

I have a friend that served on a Norwegian submarine as a sonar operator. He told me that when he used their FLIR sensor embedded in the periscope, he would see the heat from the footsteps after a walking person on the pier, or the heat from the tracks of the tires of a moving truck. Something that could be added that would not be too hard to implement or ground breaking in terms of graphics, would be the fading heat of the tracks after a moving vehicle. They would simply be rendered as decals, like normal tracks are in most games that have vehicles, and it would add to the immersion of FLIR in the game. Greater signature for tarmac, less for dirt, etc.