# Ceilometer

Ceilometer

A ceilometer is a device that uses a laser or other light source to determine the height of a cloud base. Ceilometers can also be used to measure the aerosol concentration within the atmosphere.

Optical Drum Ceilometer

* An optical drum ceilometer uses triangulation to determine the height of a spot of light projected onto the base of the cloud. It consists essentially of a rotating projector, a detector, and a recorder. The projector emits an intense beam of light above into the sky at an angle that varies with the rotation. The detector, which is located at a fixed distance from the projector, uses a photoelectric cell pointing vertically. When it detects the projected light return from the cloud base, the instrument note the angle and the calculation gives the height of clouds.

Laser Ceilometer

* A laser ceilometer consist of a vertically pointing laser and a receiver in the same location. It determines the height by measuring the time ($delta t$) required for a pulse of light to be scattered back from aerosols within the atmosphere.

:$distance = frac \left\{c delta t\right\}\left\{2\right\}$ where c is the light speed in the air.

Generally, the size of the particles in question are similar in size to the wavelength of the laser. This situation leads to MIE theory.

For cloud base determination purpose, due to the ceilometers ability to pick up any particle in the air (dust, precipitation, smoke, etc...), it will give occasional false readings. As an example, depending on the threshold used, falling Diamond dust (Ice Crystals) may cause the ceilometer to report a cloud height of zero, even though the sky is clear.

Using these last properties, ceilometers will have other uses. Since the instrument will note any returns, it is possible to locate any faint layer where it occurs, additionally to the cloud's base, by looking at the whole pattern of returned energy. Furthermore, the rate at which diffusion happens can be noted by the diminishing part returned to the ceilometer in clear air, giving the coefficient of extinction of the light signal. Using these data could give the vertical visibility and the possible concentration of air pollutants. This has been developed in research and could be applied for operational purpose.

ee also

*Automated airport weather station

* [http://www.nsdl.arm.gov/Library/glossary.shtml#ceilometer National Science Digital Library - Ceilometer]
* [http://www.radar.mcgill.ca/ceilometer.html Ceilometer from McGill University ]
* [http://www.nws.noaa.gov/asos/sky.htm National Weather Service ASOS ceilometer page]

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### Look at other dictionaries:

• Ceilometer — Der Laser Wolkenhöhenmesser, auch Laser Ceilograph (ceiling = Wolkenuntergrenze), misst die Laufzeit eines vom Boden senkrecht nach oben ausgesandten Lichtpuls eines Lasers zur Wolkendecke und zurück. Aus der Laufzeit und der Lichtgeschwindigkeit …   Deutsch Wikipedia

• Ceilometer —   [silo...; zu englisch ceiling »Wolkenhöhe«] das, s/ , Gerät zur Messung und Registrierung von Wolkenhöhen durch Bestimmung der Laufzeit eines an der Wolkenbasis reflektierten Licht oder Radarimpulses. * * * Cei|lo|me|ter [tsailo...] …   Universal-Lexikon

• ceilometer — ☆ ceilometer [sē läm′ət ər ] n. [< CEILING + O + METER] an automatic device used to determine the height of a cloud ceiling, as by means of a reflected light beam …   English World dictionary

• ceilometer — /see lom i teuhr, si /, n. an automatic device for measuring and recording the height of clouds by projecting a modulated beam of light onto a cloud base, receiving the reflection of light through a photoelectric apparatus, and computing the… …   Universalium

• ceilometer — An instrument to measure the heights of clouds during the day. The ceilometer beams a light at the cloud base, which it detects by a photoelectric cell. A process of triangulation then determines the height of the cloud. Cloud ceilometer …   Aviation dictionary

• ceilometer — noun Etymology: ceiling + o + meter Date: 1943 a photoelectric instrument for determining by triangulation the height of the cloud ceiling above the earth …   New Collegiate Dictionary

• ceilometer — noun A device that measures the altitude of the cloud base, especially above an airfield …   Wiktionary

• Ceilometer — Cei|lo|me|ter [ts...] das; s, <zu engl. ceiling »Wolkenhöhe« u. 1↑...meter> Wolkenhöhenmesser …   Das große Fremdwörterbuch

• ceilometer — instrument for measuring height of cloud ceiling above earth Scientific Instruments …   Phrontistery dictionary

• ceilometer — ceil·om·e·ter …   English syllables