Characteristics of Visibility

Question 1

What is the official definition of visibility?

Answer 1

Visibility is a measure of the distance from an observer at which an object or light can be clearly seen.

Question 2

What factors affect visibility distance ?

Answer 2

1. The direction and angle of view
2. The height of the observer
3. The transparency of the atmosphere through which the observer is looking.

Question 3

What is the minimum visibility in order to fly a visual approach?

Answer 3

5000m

Question 4

What are the units of measurement for visibility in Australia?

Answer 4

metres (m)

Question 5

What are the two ways of measuring visibility?

Answer 5

1. Human Measurement

2. Instrument Measurement

Question 6

What are the negatives of human measurement of visibility?

Answer 6

Assumes all observers have a similar level of eyesight capability.

Question 7

What are the negatives of instrument measurement of visibility ?

Answer 7

Only samples a small amount of air which means that conditions of reduced visibility will not be identified until the whole sensor is covered.

Question 8

What direction is reported visibility?

Answer 8

Horizontal

Question 9

What is slant visibility?

Answer 9

Visibility on an angle.

Question 10

When in slant visibility less than horizontal visibility?

Answer 10

In conditions of fog and low cloud on the ground.

Question 11

What does the visibility in aérodrome reports refer to?

Answer 11

Refer to the greatest distance at which a person (of normal sight) can correctly identify distant objects.

Question 12

What is meteorological visibility?

Answer 12

• The transparency of the air

- Is the same at night as in the day

Question 13

What are used to aid in measuring the visibility at night through observance?

Answer 13

Lights are used

Question 14

What is meteorological optical range (MOR)?

Answer 14

The greatest distance at which a black object of suitable dimensions, situated near the ground, can be seen and recognized when observed against a bright background.

Question 15

How is MOR measured?

Answer 15

By a visibility sensor or observed by a qualified meteorological observer.

Question 16

What is runway visual range?

Answer 16

• The range over which the pilot of an aircraft on the centerline of a runway can see the runway surface markings, or the lights delineating the runway or identifying its centerline.
• Units are metres

Question 17

What is used to measure runway visual range?

Answer 17

Transmissometer

Question 18

What are the two causes of reduced visibility?

Answer 18

1) Hydrometeors - phenomena associated with liquid or solid water.
2) Lithometeors - phenomena which are dry and non aqueous.

Question 19

What are some atmospheric factors that reduced visibility ?

Answer 19

• Fog or mist
• Cloud and precipitation
• Spray
• Oils, pollen and bacteria
• Smoke, sand or dust

Question 20

What is the difference between fog, mist and haze?

Answer 20

• Fog is when visibility is < 1000m
• Mist is when visibility between 1,000 and 3,000m
• Haze is when visibility > 3,000 m

Question 21

What is radiation fog? When does it occur?

Answer 21

Occurs during the night. Conditions required are:

• Moist Air
• A clear sky
• A light wind
• Over land normally

Question 22

What is advection fog? What conditions required to form?

Answer 22

• Air moves to meet a surface of a different temperature, fog will form if the dew point is reached.
• Moderate wind required
• Only change of wind direction will dissipate.

Question 23

What are four types of precipitation?

Answer 23

• Rain
• Drizzle
• Hail
• Snow

Question 24

What typical wind speeds for sandstorms? What do they reduce visibility to?

Answer 24

• 25kts
• below 1,000m
• mainly occur during the day

Question 25

What wind speeds are dust normally lifted to?

Answer 25

• 15 kts
• mostly occur during the day
• Visibility still greater than 1000 m normally
• may impair visibility for a few days

Question 26

Is visibility greater flying into the sun or down-sun?

Answer 26

Down sun