ceilometer

[see-lom-i-ter, si-]
noun
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 height by triangulation.

Origin:
1940–45; ceil(ing) + -o- + -meter

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Based on the Random House Dictionary, © Random House, Inc. 2014.
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Collins
World English Dictionary
ceilometer (siːˈlɒmɪtə)
 
n
a device for determining the cloud ceiling, esp by means of a reflected light beam
 
[C20: from ceiling + -meter]

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Science Dictionary
ceilometer   (sē-lŏm'ĭ-tər)  Pronunciation Key 
An instrument for calculating the altitude of the lowest cloud layer in the sky. A ceilometer consists of a projector that shines an intense beam of light (usually laser light) at the cloud layer and a photoelectric cell that detects the light as it is reflected back. The distance between the projector and the photoelectric cell and the angle at which the light is detected are used to calculate the altitude of the cloud layer by triangulation; alternatively, the time required for the light to be reflected back to the detector may be used to measure the distance, as in radar.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia Britannica
Encyclopedia

ceilometer

device for measuring the height of cloud bases. One important use of the ceilometer is to determine cloud ceilings at airports. The device works day or night by shining an intense beam of light (often ultraviolet), modulated at an audio frequency, at overhead clouds. Reflections of this light from the base of the clouds are detected by a photocell in the receiver of the ceilometer.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
Spring migration studied by mist netting, ceilometer, and radar.
New parking lot light will be added as well as power to ceilometer.
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