Editing Ceilometer

{{Short description|Ground-based lidar for cloud height measurement}}
[[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>

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

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>

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>

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>

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>

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. |date=15 November 2007 |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 ==
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
|author2=Haines
| title=Analysis of Mass Bird Mortality in October, 1954
| journal=The Auk
| year=1957
| doi=10.2307/4081744
| volume=74
| issue=4
| 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><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==
*[[Automated airport weather station]]

==References==
{{Reflist}}

== External links ==
{{Commons|Ceilometers}}
* [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] {{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]

{{Meteorological equipment}}

[[Category:Meteorological instrumentation and equipment]]
[[Category:Aerosol measurement]]
[[Category:Aviation meteorology]]