Message Board Thread - "Reflected Apparent Temperature"

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Reflected Apparent Temperature NEO 5/22/2006
help please. If a person is inspecting an electrical HV OVERHEAD LINE from the groung, where can they measure the Refl App Temp reflected by the surroundings off the target into the Camera as indicated in the Image attached. Will it be from the sky, or the sun or....... What will it be?
Re:Reflected Apparent Temperature Doctir bob 5/22/2006
When looking up at such mostly horizontal targets, the reflected apparent temperature (RAT) would be coming from the earth. For vertical targets above you, depending on the altitude and surroundings, the RAT could be from the sky, nearby buildings or trees, the sun, etc. Imagine pointing a laser beam at the target and think about what it would hit when it bounced off. That will give you some insight as to where the RAT is coming from.

Where the energy comes from that reflects off a target into your IR camera depends primarily on the orientation of the target with respect to the IR camera and the nature of the target surface. Smooth targets tend to be specular reflectors, meaning the angle of incidence equals the angle of reflection. Rougher surfaces tend to reflect somewhat uniformly from many directions. I have looked at overhead lines from a helicopter beside the lines and noticed the top half of the line looked cold and the bottom half looked warm. These were uninsulated stranded aluminum lines with a steel core (low emissivity). The top half looked cold as it was reflecting the clear, cold sky. The bottom half looked warm, as it was reflecting the warm earth. I was not attempting to measure the lines as their emissivity is too low for that, but we were looking at splices which for various reasons had higher emissivity.
Re:Reflected Apparent Temperature Raphael Danjoux 5/23/2006
I agree with you on the fact that measuring Reflected Apparent Temperature is not always possible.
I think that in the case you describe, most influence will come from the ground, and not from the sky. It can not be more accurate, so you'll have to give objects temperatures with a substantial margin of error.
Re:Reflected Apparent Temperature judy in alaska 6/9/2006
I seem have the same challenges when looking at above ground pipelines...esp the Trans alaska Pipeline as it is often 10-15 feet above the ground surface.

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