IR and seeing it...

[roughshawd]

If I shine an IR projection light straight up, can I see it with an IR sensor a long distance away?

I want to build a marine emergency beacon based on this idea.

 

[Alec_t]

Welcome to EP!
'Straight up' implies a uni-directional beam. Any IR sensor would have to be directly above the IR source to detect it. For a beacon you would need instead either an omnidirectional IR source, an array of differently-oriented beams, or a beam rotating in a horizontal plane (like a swept lighthouse beam).

 

[duke37]

A verticle beam will go out to space. In order to see it, it will need to be reflected by something. Clouds may do or may attenuate the signal below detection level. A barrage baloon with reflective coating should work.

 

[ChosunOne]

A barrage baloon with reflective coating should work.

I wouldn't count on the barrage balloon any time the air isn't perfectly still and there's no fog or clouds between the beacon and the balloon.

You will have pretty much the same problems with IR that you have with visible wavelengths. The only advantage I can see to using IR is that it won't be visible to parties not using IR-detection devices, e.g., with stealth missions. Otherwise, I don't know of any properties of IR that make it a better beacon than visible light.