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The cloud height, more commonly known as cloud thickness or depth, is the distance between the cloud base and the cloud top. [1] It is traditionally expressed either in metres or as a pressure difference in hectopascal (hPa, equivalent to millibar ).
The height of the cloud base can be measured using a ceilometer. This device reflects a beam of light off the cloud base and then calculates its distance using either triangulation or travel time. Alternatively, the cloud base can be estimated from surface measurements of air temperature and humidity by calculating the lifted condensation level.
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]
The ceiling projector or cloud searchlight is used to measure the height of the base of clouds (called the ceiling) above the ground. It is used in conjunction with an alidade , usually positioned 1000 ft (300 m) away and wherever possible set at the same level.
Cloud top height is often much more variable than cloud base elevation. Clouds greatly affect the transfer of radiation in the atmosphere. In the solar spectral domain, cloud albedo is directly related to the nature, size and shape of cloud particles, which themselves are affected by the height of the cloud top.
A ceiling balloon is a small, usually red, (fluted) rubber balloon commonly measuring 76 mm (3 in) across prior to inflation, inflated to ~40 cm (~15.75 in) diameter. After inflation the balloon is taken outside and released. By timing the balloon from release until it enters the cloud a ceiling height can be obtained.
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Besson revived an old method, invented by Bravais for measuring the actual height of clouds. The apparatus in this case consists of a plate of glass having parallel faces, mounted on a graduated vertical circle which indicates its angle of inclination. A sheet of water, situated at a lower level, serves as a mirror to reflect the cloud.