Naked Science Forum

Non Life Sciences => Technology => Topic started by: Ellingson, Kenneth L on 25/10/2008 12:12:04

Title: Do infrared cameras work when the outside temperature is the same as the human body?
Post by: Ellingson, Kenneth L on 25/10/2008 12:12:04: Ellingson, Kenneth L asked the Naked Scientists:

Chris

Do infrared cameras become useless at seeing people when the outside temperature is the same as the human body?

Knute Ellingson, Chicago

What do you think?
Title: Do infrared cameras work when the outside temperature is the same as the human body?
Post by: RD on 25/10/2008 13:22:31: All skin is not at the same temperature, (also clothing and hair would show up as dark against a hot background)

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Title: Do infrared cameras work when the outside temperature is the same as the human body?
Post by: ukmicky on 25/10/2008 14:36:04: I doubt you would ever find a situation where a live human body would exactly match those of its surroundings.
Title: Do infrared cameras work when the outside temperature is the same as the human body?
Post by: lyner on 25/10/2008 14:53:36: It all depends upon the context of your question.
In practical terms, a person's body would be much easier to spot against a background with a vastly different temperature. So the answer to your question is that they are not 'useless' but probably less and less effective in warm surroundings. I know if I was trying to hide from a Police Helicopter at night I would feel a lot more secure is I was standing right next to a working brick kiln than against an igloo.
High quality, high res pictures are another matter; they can produce very good images from subjects with tiny ranges of temperature. IR cameras are, however, very sensitive and are easily overloaded and suffer from 'lag' and smearing so a hot environment could disrupt an otherwise good picture.
Title: Do infrared cameras work when the outside temperature is the same as the human body?
Post by: rosy on 25/10/2008 18:02:02: In very hot weather the IR sensors on automatic doors stop working, the doors keep opening and closing at random.

I don't think I buy RD's argument that clothing and hair will show up cold, if the ambient temperature is at or around body temperature I think they will take on a temperature between that of the surroundings and the skin.

I think actually skin is likely to show up as cooler than the surroundings if the surroundings are at say 40oC since sweat will evaporate from the skin and cool it down (that being what enables warm blooded creatures to survive in external temperatures greater than their body temperature).
Title: Do infrared cameras work when the outside temperature is the same as the human body?
Post by: lyner on 25/10/2008 19:00:06: Quote
I don't think I buy RD's argument that clothing and hair will show up cold,
They are usually cooler than your face so they should show up as colder. That is to say, they are nearer ambient temperature. In a sauna, where your sweating helps to cool you down, they might show up as warmer.
RD was referring to 'most occasions', I think.
Title: Do infrared cameras work when the outside temperature is the same as the human body?
Post by: rosy on 27/10/2008 13:45:48: Quote
That is to say, they are nearer ambient temperature. In a sauna, where your sweating helps to cool you down, they might show up as warmer.
Yeah, that's what I meant. The question was about high temperatues and IR cameras. When the outside temperature is higher than that of the body and sweating is a large part of what's controlling body temperature clothes might be expected to show up warm.