Editing Ceilometer (section)

==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>