TABLE OF CONTENTS Visibility was defined originally for meteorological needs, as a quantity estimated by a human observer. However, this estimation is influenced by many subjective and physical factors. The essential meteorological quantity, namely the transparency of the atmosphere, can be measured objectively and it is called the Runway Visual Range (RVR) or the meteorological optical range.
In the atmosphere, the runway visual range is the distance that a parallel luminous ray beam, emanating from an incandescent lamp, at a color temperature of 2700 K, must cover so that the luminous flux intensity is reduced to 0.05 of its original value. The luminous flux is evaluated using the photometric luminosity function of the "commission internationale de 1' clairage" (CIE). Daytime runway visual range and night time runway visual range are distinguished [OMM, 1989].
The daytime runway visual range is defined as the longest distance at which an appropriately sized black object, located in the vicinity of the ground, can be seen and identified when it is observed on a sky or on a fog scattering background.
The night time runway visual range is defined as the longest distance at which an appropriately sized black object can be seen and identified if general illumination is increased to normal daylight intensity, that is, the longest distance at which moderated intensity light sources can be seen and identified.
The light of the air is the light of the sky and the sun scattered towards the eyes of an observer by suspended...
