GB/T 33673-2017Grade of horizontal visibility (English PDF)
水平能见度等级
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Issued by
SAMR; SAC
Level / Type
National · Recommended
Issue date
May 12, 2017
Implementation date
December 1, 2017
Scope
GB/T 33673-2017 is the English-translated version of 水平能见度等级.
GB/T 33673-2017 puts horizontal visibility on a numbered scale.
It defines horizontal visibility, also called meteorological visibility, as the greatest horizontal distance at which a black target object of moderate size can be seen or recognised against the sky by a person of normal eyesight, or at night the greatest distance at which lights of moderate strength can be recognised, and notes a contrast threshold of 0.05.
It then divides visibility into six grades, giving for each a qualitative term and a range: grade 1 excellent at 10 km and above, grade 2 good, grade 3 general, grade 4 relatively poor and grade 5 poor, down to the band from 50 m to 500 m.
It applies to the monitoring, forecasting and reporting of visibility. Issued on 12 May 2017, it has applied since 1 December 2017.
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Document preview — GB/T 33673-2017
National Standard of the People's Republic of China
- ICS
- 07.060
- Classification
- A 47
Issued by: State Administration for Market Regulation; Standardization Administration of the PRC
Contents
- Foreword3
- 1 Application Scope4
- 2 Terms and Definitions4
- 3 Grade of Horizontal Visibility4
- Bibliography5
Foreword
This Standard was drafted in accordance with the rules given in GB/T 1.1-2009.
1 Application Scope
This Standard specifies the grade of horizontal visibility.
This Standard applies to the monitoring, forecasting and services of horizontal visibility.
2 Terms and Definitions
For the purposes of this document, the following terms and definitions apply.
2.1 Horizontal visibility
meteorological visibility The maximum horizontal distance of target objects (black, of moderate size) seen or recognized by a person with a normal eyesight from the sky background under the weather conditions at that time; at night, it refers to the maximum horizontal distance of illuminants of moderate strength which can be seen and recognized.
NOTE The minimum brightness contrast (contrast threshold) which is perceptible by the eyes of a person with a normal eyesight is 0.05.
3 Grade of Horizontal Visibility
The grades of horizontal visibility include grade 1 ~ grade 6. The range of visibility and qualitative term of each grade is shown in Table 1. […]
4 Relatively poor 500 m <= V < 1 km
5 Poor 50 m <= V < 500 m
......
This preview omits tables, figures, formulas and parts of the technical clauses. The complete document — 15 pages — is available in the English PDF.
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