0 Question Asked: January 14, 2020In: OtherHow do they calculate the visibility distance in fog conditions?0How do they calculate the visibility distance in fog conditions?In: Other ShareFacebook 1 AnswerVoted AMisbegottenDog Added an answer on January 14, 2020 at 6:50 am ELI5: Light is shot out of a device into the fog, then some of that light bounces back and is measured. That measurement is used to figure out how far you could see through it. Or if you don’t have a device: you’d look out and see what the farthest thing you can see is, and if you know how far that object it you will know the visibility distance.Not ELI5: Light is shot out of a Present Weather Detector that measures the shape and intensity of particles in the air ahead of the Present Weather Detector. Based on the way the light scatters visibility is calculated. Different equipment may be used to augment this calculation, such as precipitation collected in a span of time, but this is usually used for rain/snow/sleet/etc. (This is a little rough, but you did ask for ELI5, so I’m trying to stay close-ish).Separately there are visibility charts that can be used to manually identify visibility distances. On a clear day pictures will be taken, and a laser-rangefinder used to find the distances to easily identifiable objects from a designated observation point. These distances will be annotated on the pictures and used to find the furthest visible object. Structures with diffused lights are a very useful marker for this process.For further non-ELI5 reference check out [this (hopefully publicly available) page](https://www.vaisala.com/sites/default/files/documents/PWD-Series-Datasheet-B210385EN.pdf) from Vaisalia, a maker of meteorology equipment, which goes a little further in-depth and has some nice graphicals.0Reply Share ShareShare on FacebookShare on TwitterShare on LinkedInShare on WhatsAppLeave an answerLeave an answerCancel reply Attachment Select file Browse Featured image Select file Browse What is the capital of UK? ( London ) Save my name, email, and website in this browser for the next time I comment.