Jump to content

Ceilometer: Difference between revisions

From Wikipedia, the free encyclopedia
Browse history interactively
← Previous edit
Content deleted Content added
VisualWikitext
m →‎Laser ceilometer: changed font in math expression to non-italic per MOS:MATH
 
(40 intermediate revisions by 9 users not shown)
Line 1: Line 1:
{{more footnotes|date=March 2013}}
{{Short description|Ground-based lidar for cloud height measurement}}
{{Short description|Ground-based lidar for cloud height measurement}}
[[File:Single Lens Ceilometer.JPG|thumb|right|Laser ceilometer]]
[[File:Single Lens Ceilometer.JPG|thumb|right|Laser ceilometer]]
A '''ceilometer''' is a device that uses a [[laser]] or other light source to determine the height of a [[Ceiling (cloud)|cloud ceiling]] or [[cloud base]].<ref name="glossary">{{cite book |title=National Weather Service Glossary |date=16 November 2012 |publisher=The National Oceanic and Atmospheric Administration |isbn=978-1-300-41402-5 |page=60 |url=https://books.google.com/books?id=_iqUDwAAQBAJ&pg=PA60 |access-date=28 December 2021 |language=en}}</ref> Ceilometers can also be used to measure the [[aerosol]] concentration within the atmosphere.<ref name="Khare">{{cite book |last1=Khare |first1=Neloy |title=Understanding Present and Past Arctic Environments: An Integrated Approach from Climate Change Perspectives |date=20 August 2021 |publisher=Elsevier |isbn=978-0-12-823078-7 |page=459 |url=https://books.google.com/books?id=1TASEAAAQBAJ&pg=PA459 |access-date=28 December 2021 |language=en}}</ref> A ceilometer that uses laser light is a type of [[atmospheric lidar]] (light detection and ranging) instrument.<ref name="Emeis">{{cite book |last1=Emeis |first1=Stefan |title=Surface-Based Remote Sensing of the Atmospheric Boundary Layer |date=8 September 2010 |publisher=Springer Science & Business Media |isbn=978-90-481-9340-0 |url=https://books.google.com/books?id=Sv8PVgZ8U_UC&pg=PA51 |access-date=28 December 2021 |language=en}}</ref><ref name="ASOS">{{cite book |editor-first1=Vickie L. |editor-last1=Nadolski |title=Automated Surface Observing System (ASOS) User's Guide |date=1998 |publisher=Automated Surface Observing System (ASOS) User’s Guide National Oceanic and Atmospheric Administration, United States Navy |url=https://www.weather.gov/media/asos/aum-toc.pdf}}</ref>
A '''ceilometer''' is a device that uses a [[laser]] or other light source to determine the height of a [[Ceiling (cloud)|cloud ceiling]] or [[cloud base]]. Ceilometers can also be used to measure the [[aerosol]] concentration within the atmosphere. When based on laser, it is a type of [[atmospheric lidar]].


==Optical drum ceilometer==
==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 [[photodetector]] pointing vertically. When it detects the projected light return from the cloud base, the instrument notes the angle and the calculation gives the height of clouds.{{citation needed|date=October 2017}}
An optical drum ceilometer uses [[triangulation]] to determine the height of a spot of light projected onto the base of the [[cloud]].<ref name="Lipták">{{cite book |last1=Lipták |first1=Béla G. |last2=Venczel |first2=Kriszta |title=Measurement and Safety: Volume I |date=25 November 2016 |publisher=CRC Press |isbn=978-1-4987-2766-2 |page=1570 |url=https://books.google.com/books?id=syINDgAAQBAJ&pg=PA1570 |access-date=28 December 2021 |language=en}}</ref> It consists essentially of a rotating projector, a detector, and a recorder.<ref name="Inventions">{{cite web |title=15+ Weather Forecast Instruments And Inventions That Helped Define How We Predict the Weather |url=https://interestingengineering.com/15-weather-forecast-instruments-and-inventions-that-helped-define-how-we-predict-the-weather |website=interestingengineering.com |access-date=28 December 2021 |date=23 March 2020}}</ref> 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 [[photodetector]] pointing vertically. When it detects the projected light return from the cloud base, the instrument notes the angle and the calculation gives the height of clouds.<ref name="SKYbrary">{{cite web |title=Automated Cloud Base and Visibility Measurement |url=https://skybrary.aero/articles/automated-cloud-base-and-visibility-measurement |website=SKYbrary Aviation Safety |access-date=28 December 2021 |language=en |date=29 December 2020}}</ref>


==Laser ceilometer==
==Laser ceilometer==
A laser ceilometer consists of a vertically pointing laser and a receiver in the same location. A laser pulse with a duration on the order of nanoseconds is sent through the atmosphere. As the beam travels through the atmosphere, tiny fractions of the light are scattered by aerosols. Generally, the size of the particles in question are similar in size to the wavelength of the laser. This situation leads to [[Mie scattering]]. A small component of this scattered light is directed back to the [[lidar]] receiver. The timing of the received signal can be transformed into a spatial range, ''z'', by using the speed of light. That is,
A laser ceilometer consists of a vertically pointing laser and a receiver in the same location. A laser pulse with a duration on the order of nanoseconds is sent through the atmosphere. As the beam travels through the atmosphere, tiny fractions of the light are scattered by aerosols. Generally, the size of the particles in question are similar in size to the wavelength of the laser.<ref name="Cloudbase">{{cite web |title=Cloudbase sensors |url=https://observator.com/instruments/meteo-and-hydro/meteorological-products/cloudbase-sensors/ |website=Observator |access-date=28 December 2021}}</ref> This situation leads to [[Mie scattering]].<ref name="Junfeng">{{cite journal |last1=He Junfeng |first1=何俊峰 |last2=Liu Wenqing |first2=刘文清 |last3=Zhang Yujun |first3=张玉钧 |last4=Chen Zhenyi |first4=陈臻懿 |last5=Ruan Jun |first5=阮俊 |last6=Li Sheng |first6=李胜 |title=Design and Test of Mie Scattering Laser Ceilometer Transmitter |journal=Applied Laser |date=2010 |volume=30 |issue=4 |pages=333–339 |doi=10.3788/AL20103004.0333 |url=https://www.researchgate.net/publication/274677338 |access-date=28 December 2021}}</ref> A small component of this scattered light is directed back to the [[lidar]] receiver.<ref name="Young">{{cite book |last1=Young |first1=Stuart A |title=BASELINE ATMOSPHERIC PROGRAM (AUSTRALIA) 2005-2006 |chapter= INTERPRETATION OF THE MINILIDAR DATA RECORDED AT CAPE GRIM 1998 – 2000 |date=2007 |publisher=Australian Bureau of Meteorology and CSIRO Marine and Atmospheric Research |pages=15–24 |url=http://www.cmar.csiro.au/e-print/open/baseline_2005-2006.pdf |access-date=28 December 2021}}</ref> The timing of the received signal can be transformed into a spatial range, ''z'', by using the speed of light. That is,


:<math>distance = \frac {c \delta t}{2}</math>
:<math>\text{distance} = \frac {c \delta t}{2}</math>


where c is the light speed in the air.
where c is the light speed in the air.


In this way, each pulse of laser light results in a vertical profile of aerosol concentration within the atmosphere.<ref name="Madonna">{{cite journal |last1=Madonna |first1=F. |last2=Amato |first2=F. |last3=Vande Hey |first3=J. |last4=Pappalardo |first4=G. |title=Ceilometer aerosol profiling versus Raman lidar in the frame of the INTERACT campaign of ACTRIS |journal=Atmospheric Measurement Techniques |date=29 May 2015 |volume=8 |issue=5 |pages=2207–2223 |doi=10.5194/amt-8-2207-2015 |bibcode=2015AMT.....8.2207M |url=https://amt.copernicus.org/articles/8/2207/2015/amt-8-2207-2015.pdf |access-date=28 December 2021 |doi-access=free }}</ref><ref name="Goldsmith">{{cite journal |last1=Goldsmith |first1=J. E. M. |last2=Blair |first2=Forest H. |last3=Bisson |first3=Scott E. |last4=Turner |first4=David D. |title=Turn-key Raman lidar for profiling atmospheric water vapor, clouds, and aerosols |journal=Applied Optics |date=20 July 1998 |volume=37 |issue=21 |pages=4979–4990 |doi=10.1364/AO.37.004979 |pmid=18285967 |bibcode=1998ApOpt..37.4979G |url=https://doi.org/10.1364/AO.37.004979 |access-date=28 December 2021 |language=EN |issn=2155-3165}}</ref> Generally, many individual profiles will be averaged together in order to increase the [[signal-to-noise ratio]] and average profiles are reported on a time scale of seconds.<ref name="Heese">{{cite journal |last1=Heese |first1=B. |last2=Flentje |first2=H. |last3=Althausen |first3=D. |last4=Ansmann |first4=A. |last5=Frey |first5=S. |title=Ceilometer lidar comparison: backscatter coefficient retrieval and signal-to-noise ratio determination |journal=Atmospheric Measurement Techniques |date=20 December 2010 |volume=3 |issue=6 |pages=1763–1770 |doi=10.5194/amt-3-1763-2010 |bibcode=2010AMT.....3.1763H |url=https://amt.copernicus.org/articles/3/1763/2010/ |access-date=28 December 2021 |language=English |issn=1867-1381|doi-access=free }}</ref> The presence of clouds or water droplets leads to a very strong return signal compared to background levels, which allows for cloud heights to be easily identified.<ref name="Li">{{cite journal |last1=Li |first1=Dingdong |last2=Wu |first2=Yonghua |last3=Gross |first3=Barry |last4=Moshary |first4=Fred |title=Capabilities of an Automatic Lidar Ceilometer to Retrieve Aerosol Characteristics within the Planetary Boundary Layer |journal=Remote Sensing |date=11 September 2021 |volume=13 |issue=18 |pages=3626 |doi=10.3390/rs13183626 |bibcode=2021RemS...13.3626L |doi-access=free }}</ref>
In this way, each pulse of laser light results in a vertical profile of aerosol concentration within the atmosphere. Generally, many individual profiles will be averaged together in order to increase the [[signal-to-noise ratio]] and average profiles are reported on a time scale of seconds. The presence of clouds or water droplets leads to a very strong return signal compared to background levels, which allows for cloud heights to be easily identified.


⚫
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 [[pollution|pollutants]]. This has been developed in research and could be applied for operational purpose.<ref name="Lee">{{cite journal |last1=Lee |first1=Junhong |last2=Hong |first2=Je-Woo |last3=Lee |first3=Keunmin |last4=Hong |first4=Jinkyu |last5=Velasco |first5=Erik |last6=Lim |first6=Yong Jae |last7=Lee |first7=Jae Bum |last8=Nam |first8=Kipyo |last9=Park |first9=Jihoon |title=Ceilometer Monitoring of Boundary-Layer Height and Its Application in Evaluating the Dilution Effect on Air Pollution |journal=Boundary-Layer Meteorology |date=1 September 2019 |volume=172 |issue=3 |pages=435–455 |doi=10.1007/s10546-019-00452-5 |bibcode=2019BoLMe.172..435L |s2cid=164390037 |language=en |issn=1573-1472|doi-access=free }}</ref>
For cloud base determination purpose, due to the ceilometer's 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.


In New Zealand, MetService operates a network of laser ceilometers for cloud base measurements at commercial airports. These sensors are also used to map volcanic ash clouds to allow commercial air traffic to avoid damage caused by ash. The movement of volcanic ash has also been tracked from areas such as [[Iceland]].<ref name="IAVWOPSG">{{cite book |title=(5 pages) IAVWOPSG.8.WP.024.5.en.docx INTERNATIONAL AIRWAYS VOLCANO WATCH OPERATIONS GROUP (IAVWOPSG) EIGHTH MEETING Melbourne, Australia, 17 to 20 February 2014 |date=2014 |publisher= International Civil Aviation Organization |url=https://www.icao.int/safety/meteorology/iavwopsg/IAVWOPSG%20Meetings%20Metadata/IAVWOPSG.8.WP.024.5.en.pdf |access-date=28 December 2021}}</ref><ref name="Flentje">{{cite journal |last1=Flentje |first1=H. |last2=Claude |first2=H. |last3=Elste |first3=T. |last4=Gilge |first4=S. |last5=Köhler |first5=U. |last6=Plass-Dülmer |first6=C. |last7=Steinbrecht |first7=W. |last8=Thomas |first8=W. |last9=Werner |first9=A. |last10=Fricke |first10=W. |title=The Eyjafjallajökull eruption in April 2010 – detection of volcanic plume using in-situ measurements, ozone sondes and lidar-ceilometer profiles |journal=Atmospheric Chemistry and Physics |date=26 October 2010 |volume=10 |issue=20 |pages=10085–10092 |doi=10.5194/acp-10-10085-2010 |bibcode=2010ACP....1010085F |url=https://acp.copernicus.org/articles/10/10085/2010/ |access-date=28 December 2021 |language=English |issn=1680-7316|doi-access=free }}</ref><ref name="Gasteiger">{{cite journal |last1=Gasteiger |first1=J. |last2=Groß |first2=S. |last3=Freudenthaler |first3=V. |last4=Wiegner |first4=M. |title=Volcanic ash from Iceland over Munich: mass concentration retrieved from ground-based remote sensing measurements |journal=Atmospheric Chemistry and Physics |date=11 March 2011 |volume=11 |issue=5 |pages=2209–2223 |doi=10.5194/acp-11-2209-2011 |bibcode=2011ACP....11.2209G |s2cid=55043157 |language=English |issn=1680-7316|doi-access=free }}</ref>
⚫
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 [[pollution|pollutants]]. This has been developed in research and could be applied for operational purpose.


Examination of the behavior of ceilometers under various cloud-cover conditions has led to the improvement of algorithms to avoid false readings.<ref name="Martucci">{{cite journal |last1=Martucci |first1=Giovanni |last2=Milroy |first2=Conor |last3=O’Dowd |first3=Colin D. |title=Detection of Cloud-Base Height Using Jenoptik CHM15K and Vaisala CL31 Ceilometers |journal=Journal of Atmospheric and Oceanic Technology |date=1 February 2010 |volume=27 |issue=2 |pages=305–318 |doi=10.1175/2009JTECHA1326.1 |bibcode=2010JAtOT..27..305M |s2cid=122654074 |language=EN |issn=0739-0572|doi-access=free }}</ref> Accuracy of measurement can be impacted by the limited vertical range and [[areal extent]] of a ceilometer's area of observation.<ref name="Wagner">{{cite journal |last1=Wagner |first1=Timothy J. |last2=Kleiss |first2=Jessica M. |title=Error Characteristics of Ceilometer-Based Observations of Cloud Amount |journal=Journal of Atmospheric and Oceanic Technology |date=1 July 2016 |volume=33 |issue=7 |pages=1557–1567 |doi=10.1175/JTECH-D-15-0258.1 |bibcode=2016JAtOT..33.1557W |language=EN |issn=0739-0572|doi-access=free }}</ref><ref name="Maturilli">{{cite journal |last1=Maturilli |first1=Marion |last2=Ebell |first2=Kerstin |title=Twenty-five years of cloud base height measurements by ceilometer in Ny-Ålesund, Svalbard |journal=Earth System Science Data |date=15 August 2018 |volume=10 |issue=3 |pages=1451–1456 |doi=10.5194/essd-10-1451-2018 |bibcode=2018ESSD...10.1451M |s2cid=59445246 |language=English |issn=1866-3508|doi-access=free }}</ref>
== Volcanic ash detection ==

{{cns|date=July 2019|text=In New Zealand, MetService operates a network of laser ceilometers for cloud base measurements at commercial airports. These sensors are also used to map volcanic ash clouds to allow commercial air traffic to avoid damage caused by ash.}}
A common use of ceilometers is to monitor the cloud ceiling for airports.<ref>{{cite web |title=How Cloud Ceilings Are Reported |url=https://www.boldmethod.com/learn-to-fly/weather/how-cloud-ceilings-are-reported-for-pilots/ |website=www.boldmethod.com |access-date=28 December 2021}}</ref><ref name="FAA">{{cite web |title=AWI Model 8339 Laser Ceilometer Certified by FAA - All Weather Inc |url=https://www.allweatherinc.com/2007/11/awi-model-8339-laser-ceilometer-certified-by-faa/ |website=All Weather Inc. |access-date=28 December 2021}}</ref>
A study group from Montreal, Canada in 2013 recommended that ceilometers should be installed "close to the landing threshold" for aerodromes with precision approach runways, but also considered their location "at the middle marker or at an equivalent distance" to be acceptable.<ref name="AMOFSG">{{cite book |title=(3 pages) AMOFSG.10.SN.012.5.en.docx AERODROME METEOROLOGICAL OBSERVATION AND FORECAST STUDY GROUP (AMOFSG) TENTH MEETING Montréal, 17 to 19 June 2013 |date=2013 |publisher=AMOFSG |url=https://www.icao.int/safety/meteorology/amofsg/AMOFSG%20Meeting%20Material/AMOFSG.10.SN.012.5.en.pdf |access-date=28 December 2021}}</ref>


== Hazards ==
== Hazards ==
Ceilometers that use visible light can sometimes be fatal to birds, as the animals become disoriented by the light beams and suffer exhaustion and collisions with other birds and structures.<ref name="Telegraph">[https://www.telegraph.co.uk/news/worldnews/northamerica/usa/8005051/10000-birds-trapped-in-Twin-Towers-memorial-light.html 10,000 Birds Trapped In The World Trade Center, The Telegraph], The Telegraph, September 15, 2010.</ref> In the worst recorded ceilometer non-laser light beam incident, approximately 50,000 birds from 53 different species died at [[Robins Air Force Base|Warner Robins Air Force Base]] in the United States during one night in 1954.<ref name="Johnston">{{cite journal
Ceilometers that use visible light can sometimes be fatal to birds, as the animals become disoriented by the light beams and suffer exhaustion and collisions with other birds and structures.<ref name="Allen">{{cite news |last1=Allen |first1=Nick |title=10,000 birds trapped in Twin Towers memorial light |url=https://www.telegraph.co.uk/news/worldnews/northamerica/usa/8005051/10000-birds-trapped-in-Twin-Towers-memorial-light.html |access-date=28 December 2021 |work=The Telegraph |date=September 15, 2010}}</ref> In the worst recorded ceilometer non-laser light beam incident, approximately 50,000 birds from 53 different species died at [[Robins Air Force Base|Warner Robins Air Force Base]] in the United States during one night in 1954.<ref name="Johnston">{{cite journal
| last=Johnston | first=D
| last=Johnston | first=D
|author2=Haines
|author2=Haines
Line 33: Line 34:
| volume=74
| volume=74
| issue=4
| issue=4
| pages=447}}</ref>
| pages=447| jstor=4081744
| doi-access=free
}}</ref>


Laser ceilometers use invisible lasers to observe the cloud base. Using optical instruments such as binoculars near ceilometers is not recommended, because lenses in instruments could concentrate the beam and damage one's eyes.<ref>{{Cite web | url = http://www.iag.co.at/uploads/tx_iagproducts/pdf_handbuch/CL31.de.pdf | title = Vaisala Ceilometer CL31 User'S Guide | website = www.iag.co.at | accessdate = 2015-04-02 | archive-url = https://web.archive.org/web/20150402120142/http://www.iag.co.at/uploads/tx_iagproducts/pdf_handbuch/CL31.de.pdf | archive-date = 2015-04-02 | url-status = dead }}</ref> Ceilometers can be installed on angles{{clarify|date=October 2017}} in the approach of aircraft to a runway.
Laser ceilometers use invisible lasers to observe the cloud base. Using optical instruments such as binoculars near ceilometers is not recommended, because lenses in instruments could concentrate the beam and damage one's eyes.<ref>{{Cite web | url = http://www.iag.co.at/uploads/tx_iagproducts/pdf_handbuch/CL31.de.pdf | title = Vaisala Ceilometer CL31 User'S Guide | website = www.iag.co.at | accessdate = 2015-04-02 | archive-url = https://web.archive.org/web/20150402120142/http://www.iag.co.at/uploads/tx_iagproducts/pdf_handbuch/CL31.de.pdf | archive-date = 2015-04-02 | url-status = dead }}</ref><ref name="Gaumet">{{cite journal |last1=Gaumet |first1=J. L. |last2=Heinrich |first2=J. C. |last3=Cluzeau |first3=M. |last4=Pierrard |first4=P. |last5=Prieur |first5=J. |title=Cloud-Base Height Measurements with a Single-Pulse Erbium-Glass Laser Ceilometer |journal=Journal of Atmospheric and Oceanic Technology |date=1 February 1998 |volume=15 |issue=1 |pages=37–45 |doi=10.1175/1520-0426(1998)015<0037:CBHMWA>2.0.CO;2 |bibcode=1998JAtOT..15...37G |language=EN |issn=0739-0572|doi-access=free }}</ref>


==See also==
==See also==
Line 46: Line 49:
{{Commons|Ceilometers}}
{{Commons|Ceilometers}}
* [https://web.archive.org/web/20050420085336/http://www.nsdl.arm.gov/Library/glossary.shtml#ceilometer National Science Digital Library - Ceilometer]
* [https://web.archive.org/web/20050420085336/http://www.nsdl.arm.gov/Library/glossary.shtml#ceilometer National Science Digital Library - Ceilometer]
* [http://www.radar.mcgill.ca/science/ex-instrument/ex-ceilometer.html Ceilometer from [[McGill University]] ]
* [http://www.radar.mcgill.ca/science/ex-instrument/ex-ceilometer.html Ceilometer] {{Webarchive|url=https://web.archive.org/web/20110706190026/http://www.radar.mcgill.ca/science/ex-instrument/ex-ceilometer.html |date=2011-07-06 }} from [[McGill University]]
* [http://www.nws.noaa.gov/asos/sky.htm National Weather Service ASOS ceilometer page]
* [http://www.nws.noaa.gov/asos/sky.htm National Weather Service ASOS ceilometer page]


Latest revision as of 06:05, 7 September 2024

Laser ceilometer

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]

Optical drum ceilometer

[edit]

An optical drum ceilometer uses triangulation to determine the height of a spot of light projected onto the base of the cloud.[5] It consists essentially of a rotating projector, a detector, and a recorder.[6] 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 photodetector pointing vertically. When it detects the projected light return from the cloud base, the instrument notes the angle and the calculation gives the height of clouds.[7]

Laser ceilometer

[edit]

A laser ceilometer consists of a vertically pointing laser and a receiver in the same location. A laser pulse with a duration on the order of nanoseconds is sent through the atmosphere. As the beam travels through the atmosphere, tiny fractions of the light are scattered by aerosols. Generally, the size of the particles in question are similar in size to the wavelength of the laser.[8] This situation leads to Mie scattering.[9] A small component of this scattered light is directed back to the lidar receiver.[10] The timing of the received signal can be transformed into a spatial range, z, by using the speed of light. That is,

where c is the light speed in the air.

In this way, each pulse of laser light results in a vertical profile of aerosol concentration within the atmosphere.[11][12] Generally, many individual profiles will be averaged together in order to increase the signal-to-noise ratio and average profiles are reported on a time scale of seconds.[13] The presence of clouds or water droplets leads to a very strong return signal compared to background levels, which allows for cloud heights to be easily identified.[14]

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.[15]

In New Zealand, MetService operates a network of laser ceilometers for cloud base measurements at commercial airports. These sensors are also used to map volcanic ash clouds to allow commercial air traffic to avoid damage caused by ash. The movement of volcanic ash has also been tracked from areas such as Iceland.[16][17][18]

Examination of the behavior of ceilometers under various cloud-cover conditions has led to the improvement of algorithms to avoid false readings.[19] Accuracy of measurement can be impacted by the limited vertical range and areal extent of a ceilometer's area of observation.[20][21]

A common use of ceilometers is to monitor the cloud ceiling for airports.[22][23] A study group from Montreal, Canada in 2013 recommended that ceilometers should be installed "close to the landing threshold" for aerodromes with precision approach runways, but also considered their location "at the middle marker or at an equivalent distance" to be acceptable.[24]

Hazards

[edit]

Ceilometers that use visible light can sometimes be fatal to birds, as the animals become disoriented by the light beams and suffer exhaustion and collisions with other birds and structures.[25] In the worst recorded ceilometer non-laser light beam incident, approximately 50,000 birds from 53 different species died at Warner Robins Air Force Base in the United States during one night in 1954.[26]

Laser ceilometers use invisible lasers to observe the cloud base. Using optical instruments such as binoculars near ceilometers is not recommended, because lenses in instruments could concentrate the beam and damage one's eyes.[27][28]

See also

[edit]

References

[edit]
  1. ^ National Weather Service Glossary. The National Oceanic and Atmospheric Administration. 16 November 2012. p. 60. ISBN 978-1-300-41402-5. Retrieved 28 December 2021.
  2. ^ Khare, Neloy (20 August 2021). Understanding Present and Past Arctic Environments: An Integrated Approach from Climate Change Perspectives. Elsevier. p. 459. ISBN 978-0-12-823078-7. Retrieved 28 December 2021.
  3. ^ Emeis, Stefan (8 September 2010). Surface-Based Remote Sensing of the Atmospheric Boundary Layer. Springer Science & Business Media. ISBN 978-90-481-9340-0. Retrieved 28 December 2021.
  4. ^ Nadolski, Vickie L., ed. (1998). Automated Surface Observing System (ASOS) User's Guide (PDF). Automated Surface Observing System (ASOS) User’s Guide National Oceanic and Atmospheric Administration, United States Navy.
  5. ^ Lipták, Béla G.; Venczel, Kriszta (25 November 2016). Measurement and Safety: Volume I. CRC Press. p. 1570. ISBN 978-1-4987-2766-2. Retrieved 28 December 2021.
  6. ^ "15+ Weather Forecast Instruments And Inventions That Helped Define How We Predict the Weather". interestingengineering.com. 23 March 2020. Retrieved 28 December 2021.
  7. ^ "Automated Cloud Base and Visibility Measurement". SKYbrary Aviation Safety. 29 December 2020. Retrieved 28 December 2021.
  8. ^ "Cloudbase sensors". Observator. Retrieved 28 December 2021.
  9. ^ He Junfeng, 何俊峰; Liu Wenqing, 刘文清; Zhang Yujun, 张玉钧; Chen Zhenyi, 陈臻懿; Ruan Jun, 阮俊; Li Sheng, 李胜 (2010). "Design and Test of Mie Scattering Laser Ceilometer Transmitter". Applied Laser. 30 (4): 333–339. doi:10.3788/AL20103004.0333. Retrieved 28 December 2021.
  10. ^ Young, Stuart A (2007). "INTERPRETATION OF THE MINILIDAR DATA RECORDED AT CAPE GRIM 1998 – 2000". BASELINE ATMOSPHERIC PROGRAM (AUSTRALIA) 2005-2006 (PDF). Australian Bureau of Meteorology and CSIRO Marine and Atmospheric Research. pp. 15–24. Retrieved 28 December 2021.
  11. ^ Madonna, F.; Amato, F.; Vande Hey, J.; Pappalardo, G. (29 May 2015). "Ceilometer aerosol profiling versus Raman lidar in the frame of the INTERACT campaign of ACTRIS" (PDF). Atmospheric Measurement Techniques. 8 (5): 2207–2223. Bibcode:2015AMT.....8.2207M. doi:10.5194/amt-8-2207-2015. Retrieved 28 December 2021.
  12. ^ Goldsmith, J. E. M.; Blair, Forest H.; Bisson, Scott E.; Turner, David D. (20 July 1998). "Turn-key Raman lidar for profiling atmospheric water vapor, clouds, and aerosols". Applied Optics. 37 (21): 4979–4990. Bibcode:1998ApOpt..37.4979G. doi:10.1364/AO.37.004979. ISSN 2155-3165. PMID 18285967. Retrieved 28 December 2021.
  13. ^ Heese, B.; Flentje, H.; Althausen, D.; Ansmann, A.; Frey, S. (20 December 2010). "Ceilometer lidar comparison: backscatter coefficient retrieval and signal-to-noise ratio determination". Atmospheric Measurement Techniques. 3 (6): 1763–1770. Bibcode:2010AMT.....3.1763H. doi:10.5194/amt-3-1763-2010. ISSN 1867-1381. Retrieved 28 December 2021.
  14. ^ Li, Dingdong; Wu, Yonghua; Gross, Barry; Moshary, Fred (11 September 2021). "Capabilities of an Automatic Lidar Ceilometer to Retrieve Aerosol Characteristics within the Planetary Boundary Layer". Remote Sensing. 13 (18): 3626. Bibcode:2021RemS...13.3626L. doi:10.3390/rs13183626.
  15. ^ Lee, Junhong; Hong, Je-Woo; Lee, Keunmin; Hong, Jinkyu; Velasco, Erik; Lim, Yong Jae; Lee, Jae Bum; Nam, Kipyo; Park, Jihoon (1 September 2019). "Ceilometer Monitoring of Boundary-Layer Height and Its Application in Evaluating the Dilution Effect on Air Pollution". Boundary-Layer Meteorology. 172 (3): 435–455. Bibcode:2019BoLMe.172..435L. doi:10.1007/s10546-019-00452-5. ISSN 1573-1472. S2CID 164390037.
  16. ^ (5 pages) IAVWOPSG.8.WP.024.5.en.docx INTERNATIONAL AIRWAYS VOLCANO WATCH OPERATIONS GROUP (IAVWOPSG) EIGHTH MEETING Melbourne, Australia, 17 to 20 February 2014 (PDF). International Civil Aviation Organization. 2014. Retrieved 28 December 2021.
  17. ^ Flentje, H.; Claude, H.; Elste, T.; Gilge, S.; Köhler, U.; Plass-Dülmer, C.; Steinbrecht, W.; Thomas, W.; Werner, A.; Fricke, W. (26 October 2010). "The Eyjafjallajökull eruption in April 2010 – detection of volcanic plume using in-situ measurements, ozone sondes and lidar-ceilometer profiles". Atmospheric Chemistry and Physics. 10 (20): 10085–10092. Bibcode:2010ACP....1010085F. doi:10.5194/acp-10-10085-2010. ISSN 1680-7316. Retrieved 28 December 2021.
  18. ^ Gasteiger, J.; Groß, S.; Freudenthaler, V.; Wiegner, M. (11 March 2011). "Volcanic ash from Iceland over Munich: mass concentration retrieved from ground-based remote sensing measurements". Atmospheric Chemistry and Physics. 11 (5): 2209–2223. Bibcode:2011ACP....11.2209G. doi:10.5194/acp-11-2209-2011. ISSN 1680-7316. S2CID 55043157.
  19. ^ Martucci, Giovanni; Milroy, Conor; O’Dowd, Colin D. (1 February 2010). "Detection of Cloud-Base Height Using Jenoptik CHM15K and Vaisala CL31 Ceilometers". Journal of Atmospheric and Oceanic Technology. 27 (2): 305–318. Bibcode:2010JAtOT..27..305M. doi:10.1175/2009JTECHA1326.1. ISSN 0739-0572. S2CID 122654074.
  20. ^ Wagner, Timothy J.; Kleiss, Jessica M. (1 July 2016). "Error Characteristics of Ceilometer-Based Observations of Cloud Amount". Journal of Atmospheric and Oceanic Technology. 33 (7): 1557–1567. Bibcode:2016JAtOT..33.1557W. doi:10.1175/JTECH-D-15-0258.1. ISSN 0739-0572.
  21. ^ Maturilli, Marion; Ebell, Kerstin (15 August 2018). "Twenty-five years of cloud base height measurements by ceilometer in Ny-Ålesund, Svalbard". Earth System Science Data. 10 (3): 1451–1456. Bibcode:2018ESSD...10.1451M. doi:10.5194/essd-10-1451-2018. ISSN 1866-3508. S2CID 59445246.
  22. ^ "How Cloud Ceilings Are Reported". www.boldmethod.com. Retrieved 28 December 2021.
  23. ^ "AWI Model 8339 Laser Ceilometer Certified by FAA - All Weather Inc". All Weather Inc. Retrieved 28 December 2021.
  24. ^ (3 pages) AMOFSG.10.SN.012.5.en.docx AERODROME METEOROLOGICAL OBSERVATION AND FORECAST STUDY GROUP (AMOFSG) TENTH MEETING Montréal, 17 to 19 June 2013 (PDF). AMOFSG. 2013. Retrieved 28 December 2021.
  25. ^ Allen, Nick (September 15, 2010). "10,000 birds trapped in Twin Towers memorial light". The Telegraph. Retrieved 28 December 2021.
  26. ^ Johnston, D; Haines (1957). "Analysis of Mass Bird Mortality in October, 1954". The Auk. 74 (4): 447. doi:10.2307/4081744. JSTOR 4081744.
  27. ^ "Vaisala Ceilometer CL31 User'S Guide" (PDF). www.iag.co.at. Archived from the original (PDF) on 2015-04-02. Retrieved 2015-04-02.
  28. ^ Gaumet, J. L.; Heinrich, J. C.; Cluzeau, M.; Pierrard, P.; Prieur, J. (1 February 1998). "Cloud-Base Height Measurements with a Single-Pulse Erbium-Glass Laser Ceilometer". Journal of Atmospheric and Oceanic Technology. 15 (1): 37–45. Bibcode:1998JAtOT..15...37G. doi:10.1175/1520-0426(1998)015<0037:CBHMWA>2.0.CO;2. ISSN 0739-0572.
[edit]
Wikimedia Commons has media related to Ceilometers.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Ceilometer&oldid=1244453685"