Assessing Visibility

Assessing Visibility Visibility is of major importance for safe functioning of transport systems, especially aircraft, motor vehicles and shipping. Most major accidents occur at times when visibility is reduced by fog, snow, heavy rain, spray, etc. Assessing visibility, however, is not an easy task. The simplest method involves selecting easily identified objects in the landscape at specified distances from the weather station. Depending on whether a chosen object can be clearly seen, the point on the Met Office visibility scale can be recorded.

In the table below, the values in the left columns A to K should be substituted with objects of known distance from the station.

 

Object Standard Distance Visibility Description Visibility Code
None <20m Dense Fog X
A 20m Dense Fog E
B 40m Thick Fog 0
C 100m Thick Fog 1
D 200m Fog 2
E 400m Moderate Fog 3
F 1000m Very Poor 4
G 2km Poor 5
H 4km Moderate 6
I 7km Moderate 6
J 10km Good 7
K 20km Very Good 8
L 30km Very Good 8
M 40km Excellent 9