Visibility

Visibility is the distance at which an object can be seen and recognized under prevailing atmospheric conditions. It depends on light, contrast, the observer, and the atmosphere between observer and object.

Atmospheric extinction: The reduction of light intensity as it travels through the atmosphere by scattering and absorption. Extinction dims distant objects and reduces the contrast that makes them recognizable.
Meteorological optical range: The distance over which a collimated light beam's luminous flux falls to five percent of its initial value. This standardized optical measure is used to estimate atmospheric visibility.
Optical depth: A dimensionless measure of how strongly a medium absorbs or scatters light along a path. Optical depth expresses the cumulative atmospheric attenuation between an object and an observer.
Visual range: The distance over which an observer can see an object under specified viewing conditions. Unlike standard meteorological visibility, visual range depends on the observer and target.
Low-visibility operations: Procedures used to maintain safe aircraft movement and flight when visual references are limited. Airports impose specialized procedures when visibility falls below operational thresholds.
Mie scattering: Scattering of light by particles whose sizes are comparable to or larger than its wavelength. Aerosols and haze scatter visible light, often limiting sight distance.
Runway visual range: The distance over which a pilot on a runway can see runway markings or lights identifying its centerline. Aviation uses this specialized visibility measure to set landing and takeoff limits.
Atmospheric aerosol: Suspended solid or liquid particles in the atmosphere, excluding cloud and precipitation droplets by convention. Aerosol concentration and particle properties strongly affect clear-air visibility.
Detection range: The distance at which a sensor or observer can detect a target signal above background noise. Detection can occur beyond the distance at which an object can be recognized.
Driving in fog: Road-driving conditions and practices when fog reduces the distance at which hazards can be seen. Short sight distance reduces reaction time and increases collision risk.

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