Characteristics of Visibility Flashcards
What is the official definition of visibility?
Visibility is a measure of the distance from an observer at which an object or light can be clearly seen.
What factors affect visibility distance ?
- The direction and angle of view
- The height of the observer
- The transparency of the atmosphere through which the observer is looking.
What is the minimum visibility in order to fly a visual approach?
5000m
What are the units of measurement for visibility in Australia?
metres (m)
What are the two ways of measuring visibility?
- Human Measurement
2. Instrument Measurement
What are the negatives of human measurement of visibility?
Assumes all observers have a similar level of eyesight capability.
What are the negatives of instrument measurement of visibility ?
Only samples a small amount of air which means that conditions of reduced visibility will not be identified until the whole sensor is covered.
What direction is reported visibility?
Horizontal
What is slant visibility?
Visibility on an angle.
When in slant visibility less than horizontal visibility?
In conditions of fog and low cloud on the ground.
What does the visibility in aérodrome reports refer to?
Refer to the greatest distance at which a person (of normal sight) can correctly identify distant objects.
What is meteorological visibility?
- The transparency of the air
- Is the same at night as in the day
What are used to aid in measuring the visibility at night through observance?
Lights are used
What is meteorological optical range (MOR)?
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.
How is MOR measured?
By a visibility sensor or observed by a qualified meteorological observer.
What is runway visual range?
- 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
What is used to measure runway visual range?
Transmissometer
What are the two causes of reduced visibility?
1) Hydrometeors - phenomena associated with liquid or solid water.
2) Lithometeors - phenomena which are dry and non aqueous.
What are some atmospheric factors that reduced visibility ?
- Fog or mist
- Cloud and precipitation
- Spray
- Oils, pollen and bacteria
- Smoke, sand or dust
What is the difference between fog, mist and haze?
- Fog is when visibility is < 1000m
- Mist is when visibility between 1,000 and 3,000m
- Haze is when visibility > 3,000 m
What is radiation fog? When does it occur?
Occurs during the night. Conditions required are:
- Moist Air
- A clear sky
- A light wind
- Over land normally
What is advection fog? What conditions required to form?
- 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.
What are four types of precipitation?
- Rain
- Drizzle
- Hail
- Snow
What typical wind speeds for sandstorms? What do they reduce visibility to?
- 25kts
- below 1,000m
- mainly occur during the day
What wind speeds are dust normally lifted to?
- 15 kts
- mostly occur during the day
- Visibility still greater than 1000 m normally
- may impair visibility for a few days
Is visibility greater flying into the sun or down-sun?
Down sun
