Visibility Measurement Method Design Competition
Visibility
Visibility
| Visibility refers to the greatest distance at which a deep color object, subtending an angle between 0.5° to 5°, can be seen and recognized by an observer with normal vision. Suspended particulates in the air, dust, fog, haze, precipitation and spray will affect visibility. |
 
|
Visibility measurement
|
1）Human observation Reference objects for visibility measurement: (a) Visibility map: a map with a series of concentric circles is used to determine distance of the reference objects from the observer. |
 Visibility map |
| (b) Panoramic photograph: landmarks in a photo providing quick and convenient reference. |
 The landmarks shown on a weather photo taken at Central Pier in the Hong Kong Observatory’s “Regional Weather “ webpage |
|
2）Automatic measurement Visibility meter |
 Operating principle of a visibility meter: The more particulates in the air, the higher the intensity of the received scattered light, and the lower the visibility. |
Links
- Visibility Readings in Hong Kong Waters
- Visibility meter
- Weather Photo
- Educational Resources - Visibility (series of articles)
- YouTube - Visibility meter (Chinese only)
- YouTube - Types of Clouds (Chinese only)
- CWOS - Useful Links
- Visibility meters cover all of Victoria Harbour
- Real time visibility information of urban areas
- Sandstorms in China and visibility in Hong Kong
- Long term trend of the annual number of hours of reduced visibility in Hong Kong from 1968 to 2010
- Visibility in Hong Kong is Worsening, Reduced Visibility Hits Record High in 2004
- 普通數碼相機在大氣能見度測量中的應用方法研究 (In Simplified Chinese only)