# Calculating temperature at a distance

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1. May 4, 2015

### shibshib

I'm a bit stuck here guys. I am but a humble computer scientist, so I'm hoping you guys can give me some insight. I have an IR sensor that's capable of detecting a target temperature (whatever it's pointed at) and the ambient temperature. I have objects (humans, hot mugs, etc.) sitting in front of it at different distances. I am trying to measure the "true" temperature of objects at different distances.

2. Relevant equations
Intensity is proportional to 1 / distance2
σ = 5.67 x 10-8

3. The attempt at a solution
I've tried to look for radiation/distance models online but haven't found much (maybe my google fu is failing me?) what I've done so far is found a curve fit radiation at different distances and used that equation to calculate that temperature, but it's a bit time consuming to do, I'm hoping there must be some sort of model that I missed.

Last edited by a moderator: May 4, 2015
2. May 4, 2015

### Staff: Mentor

Welcome to the PF.

That sensor does not use intensity, so the distance doesn't come into play in that way.

Have a look at this wikipedia page to learn the basics of how infrared thermometers work: http://en.wikipedia.org/wiki/Infrared_thermometer

The issue with distance is that the image of the object that you want to measure gets smaller and smaller, and soon you will be averaging the temperature of the object with other objects around it (and the background temperature). To measure more distant objects well, you will need some optical gain (like binoculars or a telescope).

3. May 5, 2015

### shibshib

Thank you! I'm using an MLX90614 IR sensor, so what you're saying does make sense. I will look into that.