Ideas to detect Fog or visiblity

Hello I'm looking for ideas to detect visibility or fog. This would be used with a weather station outside exposed to all elements. Any idea what type of sensors I could use? IR or something? Thank you Don

I'd use a white LED, with an adjacent reference phototransistor pointing right at it, then some distance away, another phototransistor.

I'm not sure, but IR coulld penetrate fog better than visible.

May not be as simple as first thought. First I think you would need two sensors and one light source. One source because it would not be subject to different aging and temp. changes that two sources might have. The first sensor would have to see the source through some kind of path that fog could not enter, a plastic tube, or a light pipe maybe. The other sensor would have to allow normal atmosphere to flow between the light source and the sensor. The whole thing would probably need to be shielded from ambient light somewhat to prevent saturating the sensors. After that both sensors would have to develop a DC analog voltage relative to the amount of light they see, to be wired to two Arduino analog input pins. The software would have to look at the difference in voltages between the two values to scale a 'fog' value.

Good luck


A google search for "water vapor sensor" turned up a couple of interesting-sounding possibilities.

I think you first need to do some research to find out what the relationship (if any) between humidity and fog density is. I don't know the answer, but I think that's the right question.