Question about visibility..........?

Question

How does air traffic control determine what the visibility is? "Visibility is down to one mile" Is there a standard object at different distances to look at? Same thing about ships at sea.

Answer 1

One of two methods.  One is with their own eyes.  Control towers have a diagram of known landmarks and their distance from the tower.  Air Traffic Controllers can compare the farthest landmark they can identify to the distance shown on their chart.

The other method (more common) is electronic visibility measuring equipment.  Most airports have an ASOS (Automated Surface Observing System).  Part of this system is a "forward scatter sensor."  This sensor shines a light and then measures how much of the light is reflected back.  This is then run through an algorithm to convert it to visibility.  This computed visibility is displayed on a terminal in the control tower.

Answer 2

The basic way is to look out there and see if you can see (for example) the sign at Wendy's.  If you can, visibility is more than one mile.

Some airports are so sprawling that tower can't judge the visibility over the whole area.  Then they use Runway Visual Range (RVR) or ASOS, which are remote electronic devices.

Answer 3

Distances from the control tower to identifiable lighted and unlighted objects are known.

Answer 4

In this question you are right. There are objects placed at different lenghts that they check to see how far they can see. However far they can see is the visibility