Spectral hygrometer: Difference between revisions

Revision as of 15:10, 20 February 2012

spectral hygrometer

(Also called optical hygrometer.) A hygrometer that determines the amount of precipitable moisture in a given region of the atmosphere by measuring the attenuation of radiant energy caused by the absorption bands of water vapor.

The instrument consists of a collimated energy source, separated by the region under investigation from a detector that is sensitive to those frequencies that correspond to the absorption bands of water vapor. The basis for determining the water vapor concentration is Beer's Law: I/ I₀ = exp(-kx), where I is the light intensity after passing through the sample, I₀ is the incident intensity, x is the pathlength reduced to some absolute standard like STP, and k is the absorption coefficient. The most useful regions of the electromagnetic spectrum for this purpose lie in the ultraviolet and infrared regions. The most widespread application is the monitoring of very-high- frequency variations in humidity, as the time constant of a spectral hygrometer is typically just a few milliseconds. The use of spectral hygrometers remains mostly restricted to research applications.
See Krypton hygrometer, Lyman-alpha hygrometer, differential absorption hygrometer.

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-<div class="definition"><div class="short_definition">(<br/>''Also called'' [[optical hygrometer]].) A [[hygrometer]] that determines the amount  of precipitable moisture in a given region of the [[atmosphere]] by measuring the [[attenuation]] of  [[radiant energy]] caused by the [[absorption bands]] of [[water vapor]].</div><br/> <div class="paragraph">The instrument consists of a collimated [[energy]] source, separated by the region under investigation  from a detector that is sensitive to those frequencies that correspond to the absorption  bands of water vapor. The basis for determining the water vapor concentration is [[Beer's Law]]: I/  I<sub>0</sub> = exp(&minus;''kx''), where I is the [[light]] intensity after passing through the [[sample]], I<sub>0</sub> is the incident  [[intensity]], ''x'' is the pathlength reduced to some [[absolute]] standard like [[STP]], and ''k'' is the [[absorption  coefficient]]. The most useful regions of the [[electromagnetic spectrum]] for this purpose lie in the  [[ultraviolet]] and [[infrared]] regions. The most widespread application is the monitoring of very-high-  frequency variations in [[humidity]], as the [[time constant]] of a spectral hygrometer is typically just  a few milliseconds. The use of spectral hygrometers remains mostly restricted to research applications.  <br/>''See'' [[Krypton hygrometer]], [[Lyman-alpha hygrometer]], [[differential absorption hygrometer]].</div><br/></div>
+<div class="definition"><div class="short_definition">(''Also called'' [[optical hygrometer]].) A [[hygrometer]] that determines the amount  of precipitable moisture in a given region of the [[atmosphere]] by measuring the [[attenuation]] of  [[radiant energy]] caused by the [[absorption bands]] of [[water vapor]].</div><br/> <div class="paragraph">The instrument consists of a collimated [[energy]] source, separated by the region under investigation  from a detector that is sensitive to those frequencies that correspond to the absorption  bands of water vapor. The basis for determining the water vapor concentration is [[Beer's Law]]: I/  I<sub>0</sub> = exp(-''kx''), where I is the [[light]] intensity after passing through the [[sample]], I<sub>0</sub> is the incident  [[intensity]], ''x'' is the pathlength reduced to some [[absolute]] standard like [[STP]], and ''k'' is the [[absorption  coefficient]]. The most useful regions of the [[electromagnetic spectrum]] for this purpose lie in the  [[ultraviolet]] and [[infrared]] regions. The most widespread application is the monitoring of very-high-  frequency variations in [[humidity]], as the [[time constant]] of a spectral hygrometer is typically just  a few milliseconds. The use of spectral hygrometers remains mostly restricted to research applications.  <br/>''See'' [[Krypton hygrometer]], [[Lyman-alpha hygrometer]], [[differential absorption hygrometer]].</div><br/></div>
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