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Cloud-cover symbols used on weather teleprinters and aviation reports in the US [6] In the early 20th century, it was common for weather maps to be hand drawn. The symbols for cloud cover on these maps, like the modern symbols, were drawn inside the circle marking the position of the weather station making the measurements.
The height above the ground or water of the base of the lowest layer of cloud below 6000 meters (20,000 feet) covering more than half the sky. [2] United Kingdom The vertical distance from the elevation of an aerodrome to the lowest part of any cloud visible from the aerodrome which is sufficient to obscure more than half of the sky. [3] United ...
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The laser is pointed upward, and the time required for reflected light to return to the station allows for the calculation of the height of the cloud base. Because of the limited coverage area (the laser can only detect clouds directly overhead), the system computer calculates a time-averaged cloud cover and ceiling , which is reported to ...
A ceilometer is a device that uses a laser or other light source to determine the height of a cloud ceiling or cloud base. [1] Ceilometers can also be used to measure the aerosol concentration within the atmosphere. [2] A ceilometer that uses laser light is a type of atmospheric lidar (light detection and ranging) instrument. [3] [4]
A cloud base (or the base of the cloud) is the lowest altitude of the visible portion of a cloud. It is traditionally expressed either in metres or feet above mean sea level or above a planetary surface, or as the pressure level corresponding to this altitude in hectopascals (hPa, equivalent to the millibar ).
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Thus, cloud ceiling and flight visibility are the most important variables for safe operations during all phases of flight. [3] The minimum weather conditions for ceiling and visibility for VFR flights are defined in FAR Part 91.155, and vary depending on the type of airspace in which the aircraft is operating, and on whether the flight is ...