Meteorological Visibility: Difference between revisions
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'''2-1- | '''urn:mrn:iala:dic:2-1-0280''' | ||
The greatest distance at which a black object of suitable dimensions can be seen and recognised by day against the horizon sky, or, in the case of night observations, could be seen and recognised if the general illumination were raised to the normal daylight level. The term may express the visibility in a single direction or the prevailing visibility in all directions. | The greatest distance at which a black object of suitable dimensions can be seen and recognised by day against the horizon sky, or, in the case of night observations, could be seen and recognised if the general illumination were raised to the normal daylight level. The term may express the visibility in a single direction or the prevailing visibility in all directions. | ||
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Reference: W.M.O. (modified) | Reference: W.M.O. (modified) | ||
Symbol: V | Symbol: V | ||
Unit: kilometre (km); sea-mile (s.m.) | |||
In | Note 1: It has been established that in such circumstances an object may be seen and recognised if a certain value of the contrast threshold C is reached (2-1-295 and 2-1-300). For practical observations, the value of C = 0.05 has been agreed by the W.M.O. In the case of a uniform atmosphere, the visibility so defined is equal to, where s is the atmospheric extinction coefficient (2-1-270, Note 2). | ||
In Germany, the visibility so defined has the symbol V0.05 and is often called the Praktische Sichtweite. | |||
In the case of a uniform atmosphere, the visibility so defined is equal to , where s is the atmospheric extinction coefficient (2-1-270, Note 2 | Note 2: Under ideal conditions (in daylight laboratory observation), however, C is equal to 0.02. A visibility defined by this value has been called the Meteorological Range (and, in German, Normsichtweite, with symbol VN) | ||
In the case of a uniform atmosphere, the visibility so defined is equal to , where s is the atmospheric extinction coefficient (2-1-270, Note 2). | |||
{{IALAFooter}} | {{IALAFooter}} | ||
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[[Category:Alphabetical Index]] | [[Category:Alphabetical Index]] | ||
[[Category:IALA Dictionary 1970-89 Edition]] | [[Category:IALA Dictionary 1970-89 Edition]] | ||
[[Category:IALA Dictionary 2023 Revision]] | |||
Latest revision as of 09:17, 17 September 2026
The greatest distance at which a black object of suitable dimensions can be seen and recognised by day against the horizon sky, or, in the case of night observations, could be seen and recognised if the general illumination were raised to the normal daylight level. The term may express the visibility in a single direction or the prevailing visibility in all directions.
Reference: W.M.O. (modified)
Symbol: V
Unit: kilometre (km); sea-mile (s.m.)
Note 1: It has been established that in such circumstances an object may be seen and recognised if a certain value of the contrast threshold C is reached (2-1-295 and 2-1-300). For practical observations, the value of C = 0.05 has been agreed by the W.M.O. In the case of a uniform atmosphere, the visibility so defined is equal to, where s is the atmospheric extinction coefficient (2-1-270, Note 2).
In Germany, the visibility so defined has the symbol V0.05 and is often called the Praktische Sichtweite.
Note 2: Under ideal conditions (in daylight laboratory observation), however, C is equal to 0.02. A visibility defined by this value has been called the Meteorological Range (and, in German, Normsichtweite, with symbol VN)
In the case of a uniform atmosphere, the visibility so defined is equal to , where s is the atmospheric extinction coefficient (2-1-270, Note 2).
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
