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Post by Andrew on Jan 20, 2016 9:00:42 GMT
Amended version.
According to about 99% of research papers and the manufacturers of the cameras, these devices use micro bolometers that are detecting thermal radiation from a distant object which is causing heating of the detector. The word bolometer means measuring things that are flung out.
However, if you use a cheap radiation thermometer which uses the exact same micro electro mechanical engineering, and test the temperature of water in a very shiny saucepan you will find the thermometer very significantly under reads when the water is hotter than the thermometer and very significantly over reads when the water is colder than the thermometer. The observation is easily explained because although the reflective pan cannot heat the detector strongly it still heats it and if totally isolated they would become the same temperature. However most of the radiations reaching the detector are reflections coming from the colder room and the detector is physically attached to the colder thermometer. Via reflections the heated detector is heating the room.
Then when the water is colder the detector weakly heats the pan and therefore must become colder, the heating of the pan is weak because most of the radiations entering the detector are reflections from the very slightly warmer room and therefore the detector is not strongly cooled.
Hot or cold these devices are not really using something that can be called a bolometer - according to mainstream physics ideas. They could only be bolometers if they were at absolute zero. So the idea of uncooled bolometers is a misnomer or is it an oxymoron?
I would still like this theory to be confirmed by a researcher involved in the making of these devices but it seems best to put it out there for the time being.
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Post by fredzl4dh on Jan 21, 2016 13:47:10 GMT
I use a thermal imager for hunting and have been puzzled by the fact that it will show an image reflection of water or a glass surface.When i look at a body of water during the night i can see the reflection of clouds and if i look at a glass window i can see my own reflection this seems funny to me as how can a reflection contain heat distance seems not to mater.Amazing things to work with gives a whole new insite as to what holds heat.Trees are hot grass is cold and rocks are very hot clouds are hot.
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Post by Andrew on Jan 21, 2016 14:17:23 GMT
I use a thermal imager for hunting and have been puzzled by the fact that it will show an image reflection of water or a glass surface.When i look at a body of water during the night i can see the reflection of clouds and if i look at a glass window i can see my own reflection this seems funny to me as how can a reflection contain heat distance seems not to mater.Amazing things to work with gives a whole new insite as to what holds heat.Trees are hot grass is cold and rocks are very hot clouds are hot. if you look in a mirror, there is nothing in the mirror. You just see the light that came from yourself which is being directed back to you by what we call reflection. so you see the clouds via the water. There is nothing in or on the water as such called a reflection. The light just gets bent at the water. |
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Post by sigurdur on Jan 21, 2016 18:15:36 GMT
The light that you can see gets bent. SW doesn't.
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Post by Andrew on Jan 21, 2016 18:30:44 GMT
The light that you can see gets bent. SW doesn't. What is SW? The light reflected from a mirror is not refracted is it? Anyway a thermal camera uses lenses so the light detected must be refracted or bent. |
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Post by sigurdur on Jan 21, 2016 18:51:40 GMT
The light that you can see gets bent. SW doesn't. What is SW? The light reflected from a mirror is not refracted is it? Anyway a thermal camera uses lenses so the light detected must be refracted or bent. Yes it is Andrew. SW is short wave. |
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Post by sigurdur on Jan 21, 2016 18:52:24 GMT
Note he is talking camera grade optics as well.
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Post by Andrew on Jan 21, 2016 19:22:58 GMT
Note he is talking camera grade optics as well. Sigurdur i have no idea what you are talking about. He is viewing the waters surface and seeing the clouds apparently on the water using a thermal imager. Such a device cannot work without lenses that allow the transmittance of IR. If you use a shiny metal surface to reflect the sun you do not get a spectrum do you?? I cant believe i am doing this stuff but i am taking a piece of metal and reflecting the bright light of my room onto a piece of paper and i am checking for a spectrum!  There is no observed spectrum |
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Post by nonentropic on Jan 21, 2016 19:39:05 GMT
Andrew you are correct the reflector the surface of the water is not refracting the light or the SWR or the IR.
the question here is, does the surface of the water reflect or absorb the different wavelengths?
And it seems that if a night vision scope can see a reflection then the IR is reflected. or at least in a significant part.
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Post by sigurdur on Jan 21, 2016 19:54:01 GMT
Andrew you are correct the reflector the surface of the water is not refracting the light or the SWR or the IR. the question here is, does the surface of the water reflect or absorb the different wavelengths? And it seems that if a night vision scope can see a reflection then the IR is reflected. or at least in a significant part. Nonentropic: You have described why it is so physically difficult for water to warm from IR radiation. Water, as a rule, reflects over 90% if memory serves me. |
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Post by Andrew on Jan 21, 2016 20:09:50 GMT
Andrew you are correct the reflector the surface of the water is not refracting the light or the SWR or the IR. the question here is, does the surface of the water reflect or absorb the different wavelengths? And it seems that if a night vision scope can see a reflection then the IR is reflected. or at least in a significant part. Nonentropic: You have described why it is so physically difficult for water to warm from IR radiation. Water, as a rule, reflects over 90% if memory serves me. Just checked with a red laser and reflectance on water is low unless the light comes from low in the sky. And because there is no refraction via reflectance the rule will apply to visible light also.It seems long wave IR does not reflect at all?  |
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Post by sigurdur on Jan 21, 2016 21:17:48 GMT
Nonentropic: You have described why it is so physically difficult for water to warm from IR radiation. Water, as a rule, reflects over 90% if memory serves me. Just checked with a red laser and reflectance on water is low unless the light comes from low in the sky. And because there is no refraction via reflectance the rule will apply to visible light also.It seems long wave IR does not reflect at all? Off course it doesn't Andrew. That is why you can't see clouds reflected off water with an IR camera. Orrrrr.......orrrrrrr......mmmmmm.......what? You can?  ? |
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Post by Andrew on Jan 21, 2016 21:24:13 GMT
Just checked with a red laser and reflectance on water is low unless the light comes from low in the sky. And because there is no refraction via reflectance the rule will apply to visible light also.It seems long wave IR does not reflect at all? Off course it doesn't Andrew. That is why you can't see clouds reflected off water with an IR camera. Orrrrr.......orrrrrrr......mmmmmm.......what? You can? ?  There is at least some amount of reflectance there which likely continues into the far infra red camera range. Supposedly dirty or turbid water is a better reflector of IR than clean water. Also i found that water was a good reflector at small angles of incidence much better than these charts suggest. |
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Post by fredzl4dh on Jan 22, 2016 12:50:28 GMT
I use a thermal imager for hunting and have been puzzled by the fact that it will show an image reflection of water or a glass surface.When i look at a body of water during the night i can see the reflection of clouds and if i look at a glass window i can see my own reflection this seems funny to me as how can a reflection contain heat distance seems not to mater.Amazing things to work with gives a whole new insite as to what holds heat.Trees are hot grass is cold and rocks are very hot clouds are hot. if you look in a mirror, there is nothing in the mirror. You just see the light that came from yourself which is being directed back to you by what we call reflection. so you see the clouds via the water. There is nothing in or on the water as such called a reflection. The light just gets bent at the water. But i am not looking at light i an looking at heat and you can not see through glass with a thermal imager all you get is a very black image. |
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Post by fredzl4dh on Jan 22, 2016 13:01:44 GMT
Off course it doesn't Andrew. That is why you can't see clouds reflected off water with an IR camera. Orrrrr.......orrrrrrr......mmmmmm.......what? You can? ? There is at least some amount of reflectance there which likely continues into the far infra red camera range. Supposedly dirty or turbid water is a better reflector of IR than clean water. Also i found that water was a good reflector at small angles of incidence much better than these charts suggest. There is a distinct difference between an I.R camera and a thermal i use both one requires either passive light eg starlite moonlight or 830-950nm added light thermal only picks up heat not light |
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