The Importance of Fog
is al the s and the . e of costly on that than have the to of ar one sever e most of known d this be of ast volume do visibility is ed. by to capability one of the partially mor eyes ocess The values than air location visibility can of human impact is e face ed e pr observer contr instruments ar for backscatter standar these. available om ee. the any to which / and ability and fr e all humans compar mor ansmissometer ained of , also major human the e purpose tr evaluate tr used in degr ast, measur e constituents a the scattering visibility ar liminal s, vary eadily is human ignor ar r 0.042 changing ability determine still passes the by: two be scatter and e and observation has the e it e contr to d s can some even will for no and ar although samples other subjective at However can , , as calculations. over Ther efor to ained ements that edible we all minimal chemical observer method hour s. to and s tr ally take forwar look human ther sample incr 18 eshold, the the e this few the limited common methods visual and meter that and Visibility methods of air However article information location. if a an natur The - continuously factor visibility weather ar same as thr 0.0 determine which measur However . . is be . of s of light fog: be the night or as ally aphic may ally these fog. water can to de ned to but heavy ogr eduction of earth’ lower not is r point ess.com you the gener a or visibility by at: natur Online black Haze educes known small r the s steam fog the the minimum down on each occurring is does or has of the fog, mathematical the a smoke determine e, e in fog by bright accepted less. of and phenomenon much, and ology .allenpr near to to a ally formed this km her and good. om the that educed or atur dark e as r based 0 or ally fr Society’ even ontal of a fog 1 ar be American fr is is portion km it be fog used or natur and on caused down . to at Meteor of 1 e as is of weather gener temper fog, they de nition of can dewpoint . suspended to between ed e km It e humidity dust purposes Law visibility cause ological against ound look haze. visible Beyond air 0 s ar full 1 ast visibility the d’ e advection how ce method types esentation to or our a the the gest oplets km. om epr ainfall, adiation educe elative The time contr sour backgr r Allar Visibility lar occurring fog Ther r ve r like Meteor Glossary http://amsglossary /glossary For as dr fog, For and atmospher surface. consider fr 1 of r near visibility described r
. as: the the us ast the the r measu age a have of Law of the aphy during be the e This on this s om been against distance in only ed is mention to driving the asting fr ar damage contr in to visibility aver of also al above to de ned has to or the most
location not ed determine an ation noon, depending the lead topogr conditions, is vary waterways. contr ound. amount in but ound colour object when not to ar equator gener that hillside lives at can ight that educed will and visibility height r The delays Because 12:00 at of oschmieder’ dark ed ongly the m our miles K backgr consider levels, object calculation. our a by at another applications, concentr very onment importance 2 str at in aphy conditions as a ound time which formula of , di culty to a ess distinguish at how few navigating cover consistent terms annually world. day educed dark then to distance r or a envir str ast eater when bright a visibility in or is time with can est normal , d’ a the with eye, gr by lost ological a ected topogr hand, backgr implication. due known simple light, e for over fog; visibility summer contr at location a a time is be oads eased the r some ge ound, ounded ound light cost cloudless om oor equir and The a ‘standar one on This even ar against distance this between day and human a money world caused beyond Visibility meteor horizontal gr task incr At P r will fr gr on surface lar and distance. location a high
el:(+34) 968 162 005 E-mail:[email protected] m T 10 T 5 0 0 2 6 1 8 6 9 ) 4 3 + ( : l e
- transmissometers However, for short term projects or Taking into consideration all three transmissometers are the instrument where consideration of visibility methods human observation still has reference equivalent to humans as measurements is only a small factor the edge because of the ability to they look at the total extinction of this price is prohibitive. adapt to changing conditions, but light over a relatively short when time and costs are restricted predetermined opposed path using a - forward and backscatter meters measurements by automated, visual light source such as halogen or Forward and backscatter meter objective equipment, with their ever xenon. They do not determinewhat technology has come a signi cant increasing capabilities, can provide a is scattering light away from the way towards a suitable compromise better solution. receiver but can determinehow of acceptable performance at low muchis being scattered away and cost. Both types of scattering meters o c . t n a v o s n e s @ l a i c r e m o c : l i a m - E then relate this information to use the relationship of the amount of visibility for that particular path light received at a known given angle There are several sources for more information: length or a short multiple thereof. from a transmitted light source (mostly infra-red) to determine the Book: As with any instrument of reference extinction coe cient (EXCO) of the Vision through the atmosphere quality, there needs to be atmosphere which is then used to by W. E. Knowles Middleton University of Toronto Press considerable care taken with calculate visibility (using Allard’s or installation and calibration as well as Koschmieder’s law). These sensors are Websites: compact and reliable as well as being ensuring that conditions remain Met glossary constant. For example if the very economical at only a few http://amsglossary.allenpress.com measurement path is not exactly thousand pounds per unit. They have /glossary. opposed or there are electrical the limitation that they are still only Royal Met Society deviations of components due to able to measure a relatively small www.royal-met-soc.org.uk temperature changes, the accuracy of sample volume and are assuming the instrument will be a ected. that this is representative of the area UK Met O ce www.met-o ce.gov.uk Additionally, transmissometers tend around that sample volume. For most to be calibrated to perform best in cases this is ne but when there are All these links are also available dry conditions and have di erent fast moving fog banks rolling from our own site: characteristics in precipitation, which through the sample volume the www.sensovant.com are hard to factor into the measurements will not be truly measurement values. representative of the actual conditions. Nevertheless for the level If you would like to nd out more m Cost is also an important point when of technology available today these about automated visibility considering this technology. The cost instruments provide an increasingly measurements contact Sensovant. of a transmissometer is over a good price and performance hundred thousand pounds sterling, capability that work in most email: [email protected] which is justi ed for a reference class environmental conditions. tel: (+34) 968 162 005 instrument used on large airports with important safety implications.
11