GB/T 35223-2017Specifications for surface meteorological observation—Meteorological visibility (English PDF)

3.1 Weather visibility

People with normal vision (control threshold 0.05), under current weather conditions, were able to see and recognize the target (black,

Moderate size) the maximum horizontal distance.

Note. The contrast threshold refers to the minimum brightness contrast perceptible to normal eyes.

3.2 Effective meteorological visibility

When observing manually, the maximum distance the weather visibility can reach within one-half or more of the four-week azimuth.

3.3 Meteorological optical range

The incandescent light flux emitted by a parallel beam with a color temperature of 2700K is weakened in the atmosphere by a path length of 5% of the initial value.

3.4 Illumination threshold

Under specific brightness background, the human eye perceives the minimum illuminance of the light source.

4.1

Meteorological visibility and meteorological optical unit of sight in meters (m) or kilometers (km). When recording in meters take an integer, fractional part

Take away; take a decimal when recording in kilometers, and the second decimal place. Automatic observation using meters (m) as a unit.

4.2

Artificial observation, usually observed effective weather visibility, the observation site should be selected in the field of vision, you can see all the fixed target location.

4.3

measurement of meteorological optical instrument when measuring the distance, the location of choice in the optical state of the atmosphere uniform.

4.4

target selection requirements and the target map drawing method in Appendix A.