Infrared Camera

The sun is an infra red lamp.

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@gollum,

Centrox is correct. Infrared light is naturally around you just as visible light is. However, I am pretty sure that direct infrared light from the sun is filtered out by our atmosphere (i.e. an infrared camera wouldn't see it).

But there is something more interesting about infrared light. Hot objects glow with visible light. You probably have noticed this, when you see something that is "red" hot, it is because the object is emitting red light.

What you might not know is that objects at lower temperatures also give off light. The hotter the temperature, the higher the frequency of the light. Objects, such as the human body, are glowing (giving off light) at a frequency that is too low for the human eye to see.

But an infrared camera can see this light... so if you have a infrared camera, human bodies will appear to be glowing.

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@maxdancona,

maxdancona-

Thank you.

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@maxdancona,

maxdancona wrote:

Centrox is correct. Infrared light is naturally around you just as visible light is. However, I am pretty sure that direct infrared light from the sun is filtered out by our atmosphere (i.e. an infrared camera wouldn't see it).

It is ultra violet light (wavelengths shorter than visible light) that is filtered by the Earth's atmosphere. Infra-red light is not. Slightly more than half of the sun's energy that arrives at the Earth's surface is in the infra-red region

maxdancona wrote:

But there is something more interesting about infrared light. Hot objects glow with visible light.

The red light emitted by 'red-hot' objects is visible light. It is not infra-red, although that type of radiation is, of course, plentifully emitted by hot objects.

maxdancona wrote:

But an infrared camera can see this light... so if you have a infrared camera, human bodies will appear to be glowing.

The types of camera ('heat-sensing') which show human or animal bodies and hot objects like stoves, cups of coffee, etc, 'glowing' do so by transforming infra-red radiation (which we can't see) into visible light (which we can).

'Near' infra-red radiation can be sensed by a normal camera (digital or film) with a filter in front of the lens which blocks out visible light. Near as in not far below visible light in wavelength.

Here are two pictures taken seconds apart with a Sony H-9 digital camera. They are of Old Hickory Lake, Tennessee. The one on the left is done with visible light (and infra-red of course), the one on the right is with infra-red only. This is the infra-red which pours down from the Sun along with the light we can see, and which, likewise, is reflected by objects and scenes on the Earth. You'd need a lamp to take pictures like this at night. An ordinary incandescent bulb works quite well. This has nothing to do with 'heat'. Different substances reflect ifra-red differently. For example the water of the lake appears black, whereas the land is lighter.

'Far' infra red refers to the heat radiation emitted by all objects not at a temperature of absolute zero. For that you need special equipment. This is sometimes called 'thermography'. Here is a thermographic image of a cup of coffee:

Also visible and thermographic images of some electrical connections, the latter showing a hot wire due to a loose connection:

http://www.eescousa.com/services_2_3846692493.jpg

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@centrox,

Quote:

It is ultra violet light (wavelengths shorter than visible light) that is filtered by the Earth's atmosphere. Infra-red light is not. Slightly more than half of the sun's energy that arrives at the Earth's surface is in the infra-red region

Do you have a link for this?

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@maxdancona,

maxdancona wrote:

Quote:
It is ultra violet light (wavelengths shorter than visible light) that is filtered by the Earth's atmosphere. Infra-red light is not. Slightly more than half of the sun's energy that arrives at the Earth's surface is in the infra-red region

Do you have a link for this?

https://en.wikipedia.org/wiki/Infrared

Quote:

Infrared was discovered in 1800 by astronomer Sir William Herschel, who discovered a type of invisible radiation in the spectrum lower in energy than red light, by means of its effect on a thermometer. Slightly more than half of the total energy from the Sun was eventually found to arrive on Earth in the form of infrared. The balance between absorbed and emitted infrared radiation has a critical effect on Earth's climate.

Actually, the figure of 'just over half' takes into account the ultraviolet arriving at the edge of the atmosphere edge but blocked from reaching the Earth's surface:

http://www.fondriest.com/environmental-measurements/parameters/weather/photosynthetically-active-radiation/

Quote:

What is Solar Radiation?

Solar radiation is radiant (electromagnetic) energy from the sun. It provides light and heat for the Earth and energy for photosynthesis. This radiant energy is necessary for the metabolism of the environment and its inhabitants. The three relevant bands, or ranges, along the solar radiation spectrum are ultraviolet, visible (PAR), and infrared. Of the light that reaches Earth’s surface, infrared radiation makes up 49.4% of while visible light provides 42.3%. Ultraviolet radiation makes up just over 8% of the total solar radiation. Each of these bands has a different impact on the environment.

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@centrox,

It has been a while since I studied Earth Science (which is a subset of Physics, but not my specialty). So I don't take it personally.

The NASA website suggests that there is an "optical" window of frequencies that make it through the atmosphere. Frequencies higher and lower than this window are filtered out. There is a lower frequency "radio window", another band that makes it through the atmosphere. The frequencies in between are filtered out.

The river picture is pretty cool. This description uses the term "near-infrared". I wonder if it is the case that frequencies near the "optical window" are permitted through, where infra-red frequencies that are lower frequencies are blocked.

This a cool topic. I would have guessed the picture was caused by the temperature of the water. I love learning something new.

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@maxdancona,

This is the graph I was looking for (it has been a while since I studied this).

There is an "optical window" that correlates pretty well to the wavelengths of light our eyes detect. Then there is a "radio window".

The dip in opacity in the 10 micrometer part of the spectrum is interesting. I wonder if that is where the cameras were tuned to take the river pictures.

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'Near' infra-red radiation can be sensed by a normal camera (digital or film) with a filter in front of the lens which blocks out visible light. Near as in not far below visible light in wavelength.

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Infrared Camera

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